PHYSICS - NEWTON'S LAWS OF MOTION*

Newton's Laws of Motion

There was this fellow in England named Sir Isaac Newton. A little bit stuffy, bad hair, but quite an intelligent guy. He worked on developing calculus and physics at the same time. During his work, he came up with the three basic ideas that are applied to the physics of most motion (NOT modern physics). The ideas have been tested and verified so many times over the years, that scientists now call them Newton's Three Laws of Motion. 

Sir Isaac Newton was one of the greatest scientists and mathematicians that ever lived. He was born in England on December 25, 1643. He was born the same year that Galileo died. He lived for 85 years.Isaac Newton was raised by his grandmother. He attended Free Grammar School and then went on to Trinity College Cambridge. Newton worked his way through college. While at college he became interested in math, physics, and astronomy. Newton received both a bachelors and masters degree.While Newton was in college he was writing his ideas in a journal. 
Newton had new ideas about motion, which he called his three laws of motion. He also had ideas about gravity, the diffraction of light, and forces. Newton's ideas were so good that Queen Anne knighted him in 1705. His accomplishments laid the foundations for modern science and revolutionized the world. Sir Isaac Newton died in 1727.In this lesson you will develop an understanding of each of Newton's Three Laws of Motion.

According to Newton's first law...

An object at rest will remain at rest unless acted on by an unbalanced force. An object in motion continues in motion with the same speed and in the same direction unless acted upon by an unbalanced force.

This law is often called
"the law of inertia".

First Law
The first law says that an object at rest tends to stay at rest, and an object in motion tends to stay in motion, with the same direction and speed. 

What does this mean?This means that there is a natural tendency of objects to keep on doing what they're doing. All objects resist changes in their state of motion. In the absence of an unbalanced force, an object in motion will maintain this state of motion.

Let's study the "skater" to understand this a little better.


What is the motion in this picture?

What is the unbalanced force in this picture?

What happened to the skater in this picture?  *****************************************************************************This law is the same reason why you should always wear your seatbelt.

Motion (or lack of motion) cannot change without an unbalanced force acting. 

If nothing is happening to you, and nothing does happen, you will never go anywhere. If you're going in a specific direction, unless something happens to you, you will always go in that direction. Forever. 

You can see good examples of this idea when you see video footage of astronauts. Have you ever noticed that their tools float? They can just place them in space and they stay in one place. There is no interfering force to cause this situation to change. The same is true when they throw objects for the camera. Those objects move in a straight line. If they threw something when doing a spacewalk, that object would continue moving in the same direction and with the same speed unless interfered with; for example, if a planet's gravity pulled on it 
(Note: This is a really really simple way of descibing a big idea. You will learn all the real details - and math - when you start taking more advanced classes in physics.). 

According to Newton's second law... Acceleration is produced when a force acts on a mass. The greater the mass (of the object being accelerated) the greater the amount of force needed (to accelerate the object). What does this mean?  Everyone unconsiously knows the Second Law. Everyone knows that heavier objects require more force to move the same distance as lighter objects. However, the Second Law gives us an exact relationship between force, mass, and acceleration. It can be expressed as a mathematical equation:  or FORCE = MASS times ACCELERATION Second Law The second law says that the acceleration of an object produced by a net (total) applied force is directly related to the magnitude of the force, the same direction as the force, and inversely related to the mass of the object (inverse is a value that is one over another number... the inverse of 2 is 1/2). This is an example of how Newton's Second Law works: Mike's car, which weighs 1,000 kg, is out of gas. Mike is trying to push the car to a gas station, and he makes the car go 0.05 m/s/s. Using Newton's Second Law, you can compute how much force Mike is applying to the car. Answer = 50 newtons

The second law shows:  

• that if you exert the same force on two objects of different mass, you will get different accelerations (changes in motion). 

The effect (acceleration) on the smaller mass will be greater (more noticeable). 

The effect of a 10 newton force on a baseball would be much greater than that same force acting on a truck. The difference in effect (acceleration) is entirely due to the difference in their masses. 

This is easy, let's go on to
Newton's Third Law of Motion 

According to Newton's third law...

For every action there is an equal and opposite re-action.

What does this mean? 

This means that for every force there is a reaction force that is equal in size, but opposite in direction. That is to say that whenever an object pushes another object it gets pushed back in the opposite direction equally hard.


Let's study how a rocket works to understand
Newton's Third Law. 

The rocket's action is to push down on the ground with the force of its powerful engines, and thereaction is that the ground pushes the rocket upwards with an equal force.

UP,
UP,
and
AWAY!

Third Law

The third law says that for every action (force) there is an equal and opposite reaction (force). 

Forces are found in pairs. Think about the time you sit in a chair. Your body exerts a force downward and that chair needs to exert an equal force upward or the chair will collapse. It's an issue of symmetry. 
Acting forces encounter other forces in the opposite direction. 

There's also the example of shooting a cannonball. 
When the cannonball is fired through the air (by the explosion), the cannon is pushed backward. The force pushing the ball out was equal to the force pushing the cannon back, but the effect on the cannon is less noticeable because it has a much larger mass. That example is similar to the kick when a gun fires a bullet forward. 

Write out the questions 1-8 on notebook paper & answer each question with details.  Turn in when done.  You may use your notes to help you with answers.   DUE:  10/14 1. Who was the scientist who gave us the Laws of Motion? 2. How many Laws of Motion are there? 3. What is another name for the first law of motion? 4. Which law explains why we need to wear seatbelts? 5. Which law says that force is equal to mass times acceleration (F=MA)? 6. Which law says that heavier objects require more force than lighter objects to move or accelerate them? 7. Which law explains how rockets are launched into space? 8. Which law says that for every action there is an equal and opposite reaction?

REVIEW OF NEWTON'S LAWS OF MOTION

Newton’s laws of motion are three physical laws that form the basis for classical mechanics. They describe the relationship between the forces acting on a body and its motion due to those forces. They have been expressed in several different ways over nearly three centuries, and can be summarized as follows:

1. First law: The velocity of a body remains constant unless the body is acted upon by an external force.

2. Second law: The acceleration a of a body is parallel and directly proportional to the net force F and inversely proportional to the mass m, i.e., F = ma.

3. Third law: The mutual forces of action and reaction between two bodies are equal, opposite and collinear.