WAVES #4

1. So waves are everywhere. But what makes a wave a wave? 
2. What characteristics, properties, or behaviors are shared by the phenomena that we typically characterize as being a wave? 
3. How can waves be described in a manner that allows us to understand their basic nature and qualities?

A wave can be described as a disturbance that travels through a medium from one location to another location. 

Consider a slinky wave as an example of a wave. 

• When the slinky is stretched from end to end and is held at rest, it assumes a natural position known as the equilibrium or rest position. The coils of the slinky naturally assume this position, spaced equally far apart. To introduce a wave into the slinky, the first particle is displaced or moved from its equilibrium or rest position. The particle might be moved upwards or downwards, forwards or backwards; but once moved, it is returned to its original equilibrium or rest position. The act of moving the first coil of the slinky in a given direction and then returning it to its equilibrium position creates a disturbance in the slinky. We can then observe this disturbance moving through the slinky from one end to the other. If the first coil of the slinky is given a single back-and-forth vibration, then we call the observed motion of the disturbance through the slinky a slinky pulse. A pulse is a single disturbance moving through a medium from one location to another location. However, if the first coil of the slinky is continuously and periodically vibrated in a back-and-forth manner, we would observe a repeating disturbance moving within the slinky that endures over some prolonged period of time. The repeating and periodic disturbance that moves through a medium from one location to another is referred to as a wave.

What is a Medium?

But what is meant by the word medium? A medium is a substance or material that carries the wave. You have perhaps heard of the phrase news media. The news media refers to the various institutions (newspaper offices, television stations, radio stations, etc.) within our society that carry the news from one location to another. The news moves through the media. The media doesn't make the news and the media isn't the same as the news. The news media is merely the thing that carries the news from its source to various locations. In a similar manner, a wave medium is the substance that carries a wave (or disturbance) from one location to another. The wave medium is not the wave and it doesn't make the wave; it merely carries or transports the wave from its source to other locations. In the case of our slinky wave, the medium through that the wave travels is the slinky coils. In the case of a water wave in the ocean, the medium through which the wave travels is the ocean water. In the case of a sound wave moving from the church choir to the pews, the medium through which the sound wave travels is the air in the room. And in the case of the stadium wave, the medium through which the stadium wave travels is the fans that are in the stadium.

Particle-to-Particle Interaction

To fully understand the nature of a wave, it is important to consider the medium as a collection of interacting particles. In other words, the medium is composed of parts that are capable of interacting with each other. The interactions of one particle of the medium with the next adjacent particle allow the disturbance to travel through the medium. In the case of the slinky wave, the particles or interacting parts of the medium are the individual coils of the slinky. In the case of a sound wave in air, the particles or interacting parts of the medium are the individual molecules of air. And in the case of a stadium wave, the particles or interacting parts of the medium are the fans in the stadium.

Consider the presence of a wave in a slinky. The first coil becomes disturbed and begins to push or pull on the second coil; this push or pull on the second coil will displace the second coil from its equilibrium position. As the second coil becomes displaced, it begins to push or pull on the third coil; the push or pull on the third coil displaces it from its equilibrium position. As the third coil becomes displaced, it begins to push or pull on the fourth coil. This process continues in consecutive fashion, with each individual particle acting to displace the adjacent particle. Subsequently, the disturbance travels through the medium. The medium can be pictured as a series of particles connected by springs. As one particle moves, the spring connecting it to the next particle begins to stretch and apply a force to its adjacent neighbor. As this neighbor begins to move, the spring attaching this neighbor to its neighbor begins to stretch and apply a force on its adjacent neighbor.

A Wave Transports Energy and Not Matter

When a wave is present in a medium (that is, when there is a disturbance moving through a medium), the individual particles of the medium are only temporarily displaced from their rest position. There is always a force acting upon the particles that restores them to their original position. In a slinky wave, each coil of the slinky ultimately returns to its original position. In a water wave, each molecule of the water ultimately returns to its original position. And in a stadium wave, each fan in the bleacher ultimately returns to its original position. It is for this reason, that a wave is said to involve the movement of a disturbance without the movement of matter. The particles of the medium (water molecules, slinky coils, stadium fans) simply vibrate about a fixed position as the pattern of the disturbance moves from one location to another location.

Waves are said to be an energy transport phenomenon. As a disturbance moves through a medium from one particle to its adjacent particle, energy is being transported from one end of the medium to the other. In a slinky wave, a person imparts energy to the first coil by doing work upon it. The first coil receives a large amount of energy that it subsequently transfers to the second coil. When the first coil returns to its original position, it possesses the same amount of energy as it had before it was displaced. The first coil transferred its energy to the second coil. The second coil then has a large amount of energy that it subsequently transfers to the third coil. When the second coil returns to its original position, it possesses the same amount of energy as it had before it was displaced. The third coil has received the energy of the second coil. This process of energy transfer continues as each coil interacts with its neighbor. In this manner, energy is transported from one end of the slinky to the other, from its source to another location.

This characteristic of a wave as an energy transport phenomenon distinguishes waves from other types of phenomenon. Consider a common phenomenon observed at a softball game - the collision of a bat with a ball. A batter is able to transport energy from her to the softball by means of a bat. The batter applies a force to the bat, thus imparting energy to the bat in the form of kinetic energy. The bat then carries this energy to the softball and transports the energy to the softball upon collision. In this example, a bat is used to transport energy from the player to the softball. However, unlike wave phenomena, this phenomenon involves the transport of matter. The bat must move from its starting location to the contact location in order to transport energy. In a wave phenomenon, energy can move from one location to another, yet the particles of matter in the medium return to their fixed position. A wave transports its energy without transporting matter.

Waves are seen to move through an ocean or lake; yet the water always returns to its rest position. Energy is transported through the medium, yet the water molecules are not transported. Proof of this is the fact that there is still water in the middle of the ocean. The water has not moved from the middle of the ocean to the shore. If we were to observe a gull or duck at rest on the water, it would merely bob up-and-down in a somewhat circular fashion as the disturbance moves through the water. The gull or duck always returns to its original position. The gull or duck is not transported to the shore because the water on which it rests is not transported to the shore. In a water wave, energy is transported without the transport of water.

The same thing can be said about a stadium wave. In a stadium wave, the fans do not get out of their seats and walk around the stadium. We all recognize that it would be silly (and embarrassing) for any fan to even contemplate such a thought. In a stadium wave, each fan rises up and returns to the original seat. The disturbance moves through the stadium, yet the fans are not transported. Waves involve the transport of energy without the transport of matter.

In conclusion, a wave can be described as a disturbance that travels through a medium, transporting energy from one location (its source) to another location without transporting matter. Each individual particle of the medium is temporarily displaced and then returns to its original equilibrium positioned.

Check Your Understanding

1. TRUE or FALSE:

In order for John to hear Jill, air molecules must move from the lips of Jill to the ears of John.

2. Curly and Moe are conducting a wave experiment using a slinky. Curly introduces a disturbance into the slinky by giving it a quick back and forth jerk. Moe places his cheek (facial) at the opposite end of the slinky. Using the terminology of this unit, describe what Moe experiences as the pulse reaches the other end of the slinky.

3. Mac and Tosh are experimenting with pulses on a rope. They vibrate an end up and down to create the pulse and observe it moving from end to end. How does the position of a point on the rope, before the pulse comes, compare to the position after the pulse has passed?

4. Minute after minute, hour after hour, day after day, ocean waves continue to splash onto the shore. Explain why the beach is not completely submerged and why the middle of the ocean has not yet been depleted of its water supply.

5. A medium is able to transport a wave from one location to another because the particles of the medium are ____.

a. frictionless

b. isolated from one another

c. able to interact

d. very light

****************************************************** 

False - A sound wave involves the movement of energy from one location to another, not the movement of material. The air molecules are the particles of the medium, and they are only temporarily displaced, always returning to their original position.

When the slinky reaches the end of the slinky and hits Moe in the cheek, Moe experiences a pulse of energy. The energy originated on Curly's end and is transported through the medium to Moe's end. The last particle on Moe's end transports that energy to Moe's cheek.

The point returns to its original position. Waves (and pulses) do not permanently displace particles from their rest position.

Ocean waves do not transport water. An ocean wave could not bring a single drop of water from the middle of the ocean to shore. Ocean waves can only bring energy to the shore; the particles of the medium (water) simply oscillate about their fixed position. As such, water does not pile up on the beach.

Answer: C

For a wave to be transmitted through a medium, the individual particles of the medium must be able to interact so that they can exert a push and/or pull on each other; this is the mechanism by which disturbances are transmitted through a medium.

ELECTRICITY ACTIVITIES

WHAT IS ELECTRICITY - ACTIVITY#1

ELECTRICITY CIRCUIT - ACTIVITY #2

ELECTRIC CIRCUIT - ACTIVITY  #3

HOW A BATTERY WORKS - ACTIVITY #4

BENJAMIN FRANKLIN - ELECTRICITY ACTIVIY #5

ELECTRICITY - ACTIVITY #6

ELECTRICITY - QUIZ #1

ELECTRICITY SCAVENTER HUNT #1

ELECTRICITY SCAVENGER HUNT #2

ELECTRICITY SCAVENGER HUNT #3

• Complete the hunts' answers in your notebook

ENERGY - STORED ENERGY & BATTERIES #E

Stored Energy and Batteries

Energy cannot be created or destroyed, but it can be saved in various forms. One way to store it is in the form of chemical energy in a battery. When connected in a circuit, a battery can produce electricity.

If you look at a battery, it will have two ends; a positive terminal and a negative terminal. If you connect the two terminals with wire, a circuit is formed. Electrons will flow through the wire and a current of electricity is produced.

Inside the battery, a reaction between the chemicals takes place. But reaction takes place only if there is a flow of electrons. Batteries can be stored for a long time and still work because the chemical process doesn't start until the electrons flow from the negative to the positive terminals through a circuit.

 How the Chemical Reaction Takes Place in a Battery

A very simple modern battery is the zinc-carbon battery, called the carbon battery for short.

This battery contains acidic material within and a rod of zinc down the center. Here's where knowing a little bit of chemistry helps.

When zinc is inserted into an acid, the acid begins to eat away at the zinc, releasing hydrogen gas and heat energy. The acid molecules break up into its components: usually hydrogen and other atoms. The process releases electrons from the Zinc atoms that combine with hydrogen ions in the acid to create the hydrogen gas.

If a rod of carbon is inserted into the acid, the acid does nothing to it.

But if you connect the carbon rod to the zinc rod with a wire, creating a circuit, electrons will begin to flow through the wire and combine with hydrogen on the carbon rod. This still releases a little bit of hydrogen gas but it makes less heat. Some of that heat energy is the energy that is flowing through the circuit.

The energy in that circuit can now light a light bulb in a flashlight or turn a small motor. Depending on the size of the battery, it can even start an automobile.

Eventually, the zinc rod is completely dissolved by the acid in the battery, and the battery can no longer be used.

 Sidebar

As we read in Chapter 1, Alessandro Volta created the first battery (also see our "Super Scientists" page).

Volta called his battery the Voltaic Pile. He stacked alternating layers of zinc, cardboard soaked in salt water and silver. It looked like this:

If you attach a wire to the top and bottom of the pile, you create an electric current because of the flow of electrons. Adding another layer will increase the amount of electricity produced by the pile.

 Different Types of Batteries

Different types of batteries use different types of chemicals and chemical reactions. Some of the more common types of batteries are:

• Alkaline battery – Used in Duracell® and Energizer® and other alkaline batteries. The electrodes are zinc and manganese-oxide. The electrolyte is an alkaline paste.
• Lead-acid battery – These are used in automobiles. The electrodes are made of lead and lead-oxide with a strong acid as the electrolyte.
• Lithium battery – These batteries are used in cameras for the flash bulb. They are made with lithium, lithium-iodide and lead-iodide. They can supply surges of electricity for the flash.
• Lithium-ion battery – These batteries are found in laptop computers, cell phones and other high-use portable equipment.
• Nickel-cadmium or NiCad battery – The electrodes are nickel-hydroxide and cadmium. The electrolyte is potassium-hydroxide.
• Zinc-carbon battery or standard carbon battery – Zinc and carbon are used in all regular or standard AA, C and D dry-cell batteries. The electrodes are made of zinc and carbon, with a paste of acidic materials between them serving as the electrolyte.

 Food – Another Method of Storing Energy

Batteries store energy in a chemical process, but there are other ways of storing energy. Consider the "food chain" on our planet.

Plants, like grass in a meadow, convert the sun's energy through photosynthesis into stored chemical energy. This energy is stored in the plant cells is used by the plant to grow, repair itself and reproduce itself.

Cows and other animals eat the energy stored in the grass or grain and convert that energy into stored energy in their bodies. When we eat meat and other animal products, we in turn, store that energy in our own bodies. We use the stored energy to walk, run, ride a bike or even read a page on the Internet.

BATTERIES 101

Carefully Review:

• Battery parts

• Constructing the Battery

• Powering the Device

Flashlights 101

Carefully Review:

Whether you are outdoors for a nighttime adventure or find yourself in the dark from a power outage after a storm, flashlights put the power of light in the palm of your hand. Find out how they do it and much more.

• Parts of the Flashlight

light bulbs

• 
  

ENERGY - CIRCUITS #D

Circuits

Electrons with a negative charge, can't "jump" through the air to a positively charged atom. They have to wait until there is a link or bridge between the negative area and the positive area. We usually call this bridge a "circuit."

When a bridge is created, the electrons begin moving quickly. Depending on the resistance of the material making up the bridge, they try to get across as fast as they can. If you're not careful, too many electrons can go across at one time and destroy the "bridge" or the circuit, in the process.

In Chapter 3, we learned about electrons and the attraction between positive and negative charges. We also learned that we can create a bridge called a "circuit" between the charges.

We can limit the number of electrons crossing over the "circuit," by letting only a certain number through at a time. And we can make electricity do something for us while they are on their way. For example, we can "make" the electrons "heat" a filament in a bulb, causing it to glow and give off light.

When we limit the number of electrons that can cross over our circuit, we say we are giving it "resistance". We "resist" letting all the electrons through. This works something like a tollbooth on a freeway bridge. Copper wire is just one type of bridge we use in circuits.

Before electrons can move far, however, they can collide with one of the atoms along the way. This slows them down or even reverses their direction. As a result, they lose energy to the atoms. This energy appears as heat, and the scattering is a resistance to the current.

Think of the bridge as a garden hose. The current of electricity is the water flowing in the hose and the water pressure is the voltage of a circuit. The diameter of the hose is the determining factor for the resistance.

Current refers to the movement of charges. In an electrical circuit – electrons move from the negative pole to the positive. If you connected the positive pole of an electrical source to the negative pole, you create a circuit. This charge changes into electrical energy when the poles are connected in a circuit – similar to connecting the two poles on opposite ends of a battery.

Along the circuit you can have a light bulb and an on-off switch. The light bulb changes the electrical energy into light and heat energy.

 Circuit Experiment

As a boy, Thomas Edisonbuilt a small laboratory in his cellar. His early experiments helped develop a very inquisitive mind. His whole life was spent thinking about how things work and dreaming up new inventions. The light bulb and movie projector are just two of dozens of inventions.

You can build a very basic electrical circuit similar to what Edison may have crafted as a boy. And you can find out what happens when a current is "open" compared with when it's "closed."

Here's What You need:

1. Penlight bulb
2. Flashlight battery
3. Two 6" pieces of insulated wire (any kind will work)
4. Tape to keep the wire on the end of the battery
5. A small piece of thin flat metal to make a "switch"
6. Small block of wood

Here's What to Do

1. To make a switch:
• Take the block of wood and stick one thumb tack in.
• Push the other thumbtack through the thin piece of flat metal.
• Push the thumb tack into the wood so that the piece of metal can touch the other thumb tack (see picture).


2. Connect the first piece of wire to a thumbtack on the switch.
3. Place the light bulb in the center of this wire piece.
4. Tape the end of the first piece of wire to one end of the battery.
5. Tape your second piece of wire to the opposite end of the battery.
6. Attach the end of your second piece of wire to the remaining thumbtack on the switch.

You've created an electrical circuit.

When you press the switch connecting the two thumbtacks, your circuit is "closed" and your current flows – turning your light bulb on. When your switch is up, your circuit is "open" and your current can not flow – turning your light bulb off, just like Thomas Edison's may have done.

The number of electrons we are willing to let across the circuit at one time is called "current". We measure current using amperes, or "Amps".

One AMP is defined as 6,250,000,000,000,000,000 (6.25 x 1018) electrons moving across your circuit every second!

Since no one wants to remember such a big number, that big number is called a "coulomb," after the scientist Charles A Coulomb who helped discover what a current of electricity is.

The amount of charge between the sides of the circuit is called "voltage." We measure Voltage in Volts. The word volt is named after another scientist, Alexader Volta, who built the world's first battery.

You'll remember that back in Chapter 1, we defined energy as the "ability to do work."

Well, one volt is defined as the amount of electrical charge needed to make one Coulomb (625,000,000,000,000,000,000 electrons) do one a specific amount of work – which is labeled one joule.

Joule is also named after a scientist, James Prescott Joule. Do you remember him from Chapter 2?

Voltage, Current and Resistance are very important to circuits. If either voltage or current is too big you could break the circuit. But if either is too small, the circuit will not be able to work enough to be useful to us. In the same way, if the resistance is too big none of the electrons would be able to get though at all, but if it were too small, they would rush though all at once breaking the circuit on their way.

 Parallel Circuits!

When we have only one circuit that electrons can go through to get to the other side we call it a "series circuit."

If we were to set up another circuit next to the first one, we would have two circuits between the charges. We call these "parallel circuits" because they run parallel to each other. You can have as many parallel circuits as you want. Parallel circuits share the same voltage, but they allow more paths for the electricity to go over. This means that the total number of electrons that can get across (the current) can increase, without breaking either circuit.

 Electric Motors

An electric motor uses circuits wound round and round. These wound circuits are suspended between magnets. (We send a 'thank you' to How Stuff Works Website for their electric motor graphic.)

A motor works through electromagnetism. It has a coiled up wire (the circuit) that sits between the north and south poles of a magnet. When current flows through the coiled circuit, another magnetic field is produced. The north pole of the fixed magnet attracts the south pole of the coiled wire. The two north poles push away, or repulse, each other. The motor is set up in a way that attraction and repulsion spins the center section with the coiled wire.

ELECTRICITY - RESISTANCE & STATIC ELECTRICITY #C

Resistance and Static Electricity

As we have learned, some kinds of atoms contain loosely attached electrons. Electrons can be made to move easily from one atom to another. When those electrons move among the atoms of matter, a current of electricity is created.

Take a piece of wire. The electrons are passed from atom to atom, creating an electrical current from one end to the other. Electrons are very, very small. A single copper penny contains more than 10,000,000,000,000,000,000,000 (1x1022) electrons.

Electricity "flows" or moves through some things better than others do. The measurement of how well something conducts electricity is called its resistance.

Resistance in wire depends on how thick and how long it is, and what it's made of. The thickness of wire is called its gauge. The smaller the gauge, the bigger the wire. Some of the largest thicknesses of regular wire is gauge 1.

Different types of metal are used in making wire. You can have copper wire, aluminum wire, even steel wire. Each of these metals has a different resistance; how well the metal conducts electricity. The lower the resistance of a wire, the better it conducts electricity.

Copper is used in many wires because it has a lower resistance than many other metals. The wires in your walls, inside your lamps and elsewhere are usually copper.

A piece of metal can be made to act like a heater. When an electrical current occurs, the resistance causes friction and the friction causes heat. The higher the resistance, the hotter it can get. So, a coiled wire high in resistance, like the wire in a hair dryer, can be very hot.

Some things conduct electricity very poorly. These are called insulators. Rubber is a good insulator, and that's why rubber is used to cover wires in an electric cord. Glass is another good insulator. If you look at the end of a power line, you'll see that it is attached to some bumpy looking things. These are glass insulators. They keep the metal of the wires from touching the metal of the towers.

 Static Electricity

Another type of electrical energy is static electricity. Unlike current electricity that moves, static electricity stays in one place.

Try this experiment...

Rub a balloon filled with air on a wool sweater or on your hair. Then hold it up to a wall. The balloon will stay there by itself.

Tie strings to the ends of two balloons. Now rub the two balloons together, hold them by strings at the end and put them next to each other. They'll move apart.

Rubbing the balloons gives them static electricity. When you rub the balloon it picks up extra electrons from the sweater or your hair and becomes slightly negatively charged.

The negative charges in the single balloon are attracted to the positive charges in the wall.

The two balloons hanging by strings both have negative charges. Negative charges always repel negative charges and positive always repels positive charges. So, the two balloons' negative charges "push" each other apart.

Static electricity can also give you a shock. If you walk across a carpet, shuffling your feet and touching something made of metal, a spark can jump between you and the metal object. Shuffling your feet picks up additional electrons spread over your body. When you touch a metal doorknob or something with a positive charge the electricity jumps across the small gap from your fingers just before you touch the metal knob. If you walk across a carpet and touch a computer case, you can damage the computer.

One other type of static electricity is very spectacular. It's the lightning in a thunder and lightning storm. Clouds become negatively charged as ice crystals inside the clouds rub up against each other. Meanwhile, on the ground, the positive charge increases. The clouds get so highly charged that the electrons jump from the ground to the cloud, or from one cloud to another cloud. This causes a huge spark of static electricity in the sky that we call lightning.

You can find out more about lightning at Web Weather for Kids -www.ucar.edu/40th/webweather/

 But What Is Static Electricity?

You'll remember from Chapter 2 that the word "electricity" came from the Greek words "elektor," for "beaming sun" and "elektron," both words describing amber. Amber is fossilized tree sap millions of years old and has hardened as hard as a stone.

Around 600 BCE (Before the Common Era) Greeks noticed a strange effect: When rubbing "elektron" against a piece of fur, the amber would start attracting particles of dust, feathers and straw. No one paid much attention to this "strange effect" until about 1600 when Dr. William Gilbert investigated the reactions of magnets and amber and discovered other objects can be made "electric."

Gilbert said that amber acquired what he called "resinous electricity" when rubbed with fur. Glass, however, when rubbed with silk, acquired what he termed "vitreous electricity."

He thought that electricity repeled the same kind and attracts the opposite kind of electricity. Gilbert and other scientists of that time thought that the friction actually created the electricity (their word for the electrical charge).

In 1747, Benjamin Franklin in America and William Watson in England both reached the same conclusion. They said all materials possess a single kind of electrical "fluid." They didn't really know anything about atoms and electrons, so they called how it behaved a "fluid."

They thought that this fluid can penetrate matter freely and couldn't be created or destroyed. The two men thought that the action of rubbing (like rubbing amber with fur) moves this unseen fluid from one thing to another, electrifying both.

Franklin defined the fluid as positive and the lack of fluid as negative. Therefore, according to Franklin, the direction of flow was from positive to negative. Today, we know that the opposite is true. Electricity flows from negative to positive. Others took the idea even further saying this that two fluids are involved. They said items with the same fluid attract each other. And opposite types of fluid in objects will make them repel each other.

All of this was only partially right. This is how scientific theories develop. Someone thinks of why something occurs and then proposes an explanation. It can take centuries sometime to find the real truth. Instead of electricity being a fluid, it is the movement of the charged particles between the objects... the two objects are really exchanging electrons.

ELECTRICITY - WHAT IS ELECTRICITY? #B

What Is Electricity?

Electricity figures everywhere in our lives. Electricity lights up our homes, cooks our food, powers our computers, television sets, and other electronic devices. Electricity from batteries keeps our cars running and makes our flashlights shine in the dark.

Here's something you can do to see the importance of electricity. Take a walk through your school, house or apartment and write down all the different appliances, devices and machines that use electricity. You'll be amazed at how many things we use each and every day that depend on electricity.

But what is electricity? Where does it come from? How does it work? Before we understand all that, we need to know a little bit about atoms and their structure.

All matter is made up of atoms, and atoms are made up of smaller particles. The three main particles making up an atom are the proton, the neutron and the electron.

Electrons spin around the center, or nucleus, of atoms, in the same way the moon spins around the earth. The nucleus is made up of neutrons and protons.

Electrons contain a negative charge, protons a positive charge. Neutrons are neutral – they have neither a positive nor a negative charge.

There are many different kinds of atoms, one for each type of element. An atom is a single part that makes up an element. There are 118 different known elements that make up every thing! Some elements like oxygen we breathe are essential to life.

Each atom has a specific number of electrons, protons and neutrons. But no matter how many particles an atom has, the number of electrons usually needs to be the same as the number of protons. If the numbers are the same, the atom is called balanced, and it is very stable.

So, if an atom had six protons, it should also have six electrons. The element with six protons and six electrons is called carbon. Carbon is found in abundance in the sun, stars, comets, atmospheres of most planets, and the food we eat. Coal is made of carbon; so are diamonds.

Some kinds of atoms have loosely attached electrons. An atom that loses electrons has more protons than electrons and is positively charged. An atom that gains electrons has more negative particles and is negatively charge. A "charged" atom is called an "ion."

Electrons can be made to move from one atom to another. When those electrons move between the atoms, a current of electricity is created. The electrons move from one atom to another in a "flow." One electron is attached and another electron is lost.

This chain is similar to the fire fighter's bucket brigades in olden times. But instead of passing one bucket from the start of the line of people to the other end, each person would have a bucket of water to pour from one bucket to another. The result was a lot of spilled water and not enough water to douse the fire. It is a situation that's very similar to electricity passing along a wire and a circuit. The charge is passed from atom to atom when electricity is "passed."

Scientists and engineers have learned many ways to move electrons off of atoms. That means that when you add up the electrons and protons, you would wind up with one more proton instead of being balanced.

Since all atoms want to be balanced, the atom that has been "unbalanced" will look for a free electron to fill the place of the missing one. We say that this unbalanced atom has a "positive charge" (+) because it has too many protons.

Since it got kicked off, the free electron moves around waiting for an unbalanced atom to give it a home. The free electron charge is negative, and has no proton to balance it out, so we say that it has a "negative charge" (-).

So what do positive and negative charges have to do with electricity?

Scientists and engineers have found several ways to create large numbers of positive atoms and free negative electrons. Since positive atoms want negative electrons so they can be balanced, they have a strong attraction for the electrons. The electrons also want to be part of a balanced atom, so they have a strong attraction to the positive atoms. So, the positive attracts the negative to balance out.

The more positive atoms or negative electrons you have, the stronger the attraction for the other. Since we have both positive and negative charged groups attracted to each other, we call the total attraction "charge."

Energy also can be measured in joules. Joules sounds exactly like the word jewels, as in diamonds and emeralds. A thousand joules is equal to a British thermal unit.

When electrons move among the atoms of matter, a current of electricity is created. This is what happens in a piece of wire. The electrons are passed from atom to atom, creating an electrical current from one end to other, just like in the picture.

Electricity is conducted through some things better than others do. Its resistance measures how well something conducts electricity. Some things hold their electrons very tightly. Electrons do not move through them very well. These things are called insulators. Rubber, plastic, cloth, glass and dry air are good insulators and have very high resistance.

Other materials have some loosely held electrons, which move through them very easily. These are called conductors. Most metals – like copper, aluminum or steel – are good conductors.

 Where Does the Word 'Electricity' Come From?

Electrons, electricity, electronic and other words that begin with "electr..." all originate from the Greek word "elektor," meaning "beaming sun." In Greek, "elektron" is the word for amber.

Amber is a very pretty goldish brown "stone" that sparkles orange and yellow in sunlight. Amber is actually fossilized tree sap! It's the stuff used in the movie "Jurassic Park." Millions of years ago insects got stuck in the tree sap. Small insects which had bitten the dinosaurs, had blood with DNA from the dinosaurs in the insect's bodies, which were now fossilized in the amber.

Ancient Greeks discovered that amber behaved oddly - like attracting feathers - when rubbed by fur or other objects. They didn't know what it was that caused this phenomenon. But the Greeks had discovered one of the first examples of static electricity (see Chapter 3).

The Latin word, electricus, means to "produce from amber by friction."

So, we get our English word electricity from Greek and Latin words that were about amber.

MAGNETS & ELECTRIC CURRENTS -VIDEO


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ELECTRICITY - ENERGY - WHAT IS IT? #A

READ EACH MODULE LABELED BY  LETTERS, READ CAREFULLY.  

• THEN GO BACK & USE THE CLOZE TO HELP YOU LEARN SPECIFICS.  

Energy - What Is It?

Energy causes things to happen around us. Look out the window.

During the day, the sun gives out light and heat energy. At night, street lamps use electrical energy to light our way.

When a car drives by, it is being powered by gasoline, a type of stored energy.

The food we eat contains energy. We use that energy to work and play.

We learned the definition of energy in the introduction:

"Energy Is the Ability to Do Work."

Energy can be found in a number of different forms. It can be chemical energy, electrical energy, heat (thermal energy), light (radiant energy), mechanical energy, and nuclear energy.

 Stored and Moving Energy

Energy makes everything happen and can be divided into two types:

• Stored energy is called potential energy.
• Moving energy is called kinetic energy.

With a pencil, try this example to know the two types of energy.

Put the pencil at the edge of the desk and push it off to the floor. The moving pencil uses kinetic energy.

Now, pick up the pencil and put it back on the desk. You used your own energy to lift and move the pencil. Moving it higher than the floor adds energy to it. As it rests on the desk, the pencil has potential energy. The higher it is, the further it could fall. That means the pencil has more potential energy.

 How Do We Measure Energy?

Energy is measured in many ways.

One of the basic measuring blocks is called a Btu. This stands for British thermal unit and was invented by, of course, the English.

Btu is the amount of heat energy it takes to raise the temperature of one pound of water by one degree Fahrenheit, at sea level.

One Btu equals about one blue-tip kitchen match.

One thousand Btus roughly equals: One average candy bar or 4/5 of a peanut butter and jelly sandwich.

It takes about 2,000 Btus to make a pot of coffee.

Energy also can be measured in joules. Joules sounds exactly like the word jewels, as in diamonds and emeralds. A thousand joules is equal to a British thermal unit.

1,000 joules = 1 Btu

So, it would take 2 million joules to make a pot of coffee.

The term "joule" is named after an English scientist James Prescott Joule who lived from 1818 to 1889. He discovered that heat is a type of energy.

One joule is the amount of energy needed to lift something weighing one pound to a height of nine inches. So, if you lifted a five-pound sack of sugar from the floor to the top of a counter (27 inches), you would use about 15 joules of energy.

Around the world, scientists measure energy in joules rather than Btus. It's much like people around the world using the metric system of meters and kilograms, instead of the English system of feet and pounds.

Like in the metric system, you can have kilojoules — "kilo" means 1,000.

1,000 joules = 1 kilojoule = 1 Btu

A piece of buttered toast contains about 315 kilojoules (315,000 joules) of energy. With that energy you could:

• Jog for 6 minutes
• Bicycle for 10 minutes
• Walk briskly for 15 minutes
• Sleep for 1-1/2 hours
• Run a car for 7 seconds at 80 kilometers per hour (about 50 miles per hour)
• Light a 60-watt light bulb for 1-1/2 hours
• Or lift that sack of sugar from the floor to the counter 21,000 times!

 Changing Energy

Energy can be transformed into another sort of energy. But it cannot be created AND it cannot be destroyed. Energy has always existed in one form or another.

Here are some changes in energy from one form to another.

Stored energy in a flashlight's batteries becomes light energy when the flashlight is turned on.

Food is stored energy. It is stored as a chemical with potential energy. When your body uses that stored energy to do work, it becomes kinetic energy.

If you overeat, the energy in food is not "burned" but is stored as potential energy in fat cells.

When you talk on the phone, your voice is transformed into electrical energy, which passes over wires (or is transmitted through the air). The phone on the other end changes the electrical energy into sound energy through the speaker.

A car uses stored chemical energy in gasoline to move. The engine changes the chemical energy into heat and kinetic energy to power the car.

A toaster changes electrical energy into heat and light energy. (If you look into the toaster, you'll see the glowing wires.)

A television changes electrical energy into light and sound energy.

 Food Energy

Energy changes form at each step in the food chain. Take an ear of corn as an example.

Sunlight is taken in by the leaves on the corn stalk and transformed through photosynthesis. The plant takes in sunlight and combines it with carbon dioxide from the air and water and minerals from the ground.

The plant grows tall and creates the ears of corn - its seeds. The energy of the sunlight is stored in the leaves and inside the corn kernels. The corn kernels are full of energy stored as sugars and starch. The corn is harvested and is fed to chickens and other animals. The chickens use the stored energy in the corn on the cob to grow and to move. Some energy is stored in the animal in its muscle tissue (protein) and in the fat.

The chicken reaches maturity, a farmer slaughters it and prepares it to be sold. It's transported to the grocery store. Your parents buy the chicken at the supermarket, bring it home and cook it (using energy).

You then eat the chicken's meat and fat and convert that stored energy into energy in your own body. Maybe you ate the chicken at a picnic. Then you went and played baseball. You're using the energy from that chicken to swing the bat, run the bases and throw the ball.

As your body uses the energy from the chicken, you breathe in oxygen and exhale carbon dioxide. That carbon dioxide is then used by other plants to grow.

So, it's a big circle!

Heat Energy 

Heat is a form of energy. We use it for a lot of things, like warming our homes and cooking our food.

Heat energy moves in three ways:

1. Conduction
2. Convection
3. Radiation

Conduction occurs when energy is passed directly from one item to another. If you stirred a pan of soup on the stove with a metal spoon, the spoon will heat up. The heat is being conducted from the hot area of the soup to the colder area of spoon.

Metals are excellent conductors of heat energy. Wood or plastics are not. These "bad" conductors are called insulators. That's why a pan is usually made of metal while the handle is made of a strong plastic.

Convection is the movement of gases or liquids from a cooler spot to a warmer spot. If a soup pan is made of glass, we could see the movement of convection currents in the pan. The warmer soup moves up from the heated area at the bottom of the pan to the top where it is cooler. The cooler soup then moves to take the warmer soup's place. The movement is in a circular pattern within the pan (see picture above).

The wind we feel outside is often the result of convection currents. You can understand this by the winds you feel near an ocean. Warm air is lighter than cold air and so it rises. During the daytime, cool air over water moves to replace the air rising up as the land warms the air over it. During the nighttime, the directions change - the surface of the water is sometimes warmer and the land is cooler.

Radiation is the final form of movement of heat energy. The sun's light and heat cannot reach us by conduction or convection because space is almost completely empty. There is nothing to transfer the energy from the sun to the earth.

The sun's rays travel in straight lines called heat rays. When it moves that way, it is called radiation.

When sunlight hits the earth, its radiation is absorbed or reflected. Darker surfaces absorb more of the radiation and lighter surfaces reflect the radiation. So you would be cooler if you wear light or white clothes in the summer.

ENERGY - VIDEO

ENERGY TRANSFER & STORAGE

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