Review these video clips & ADD information you need to your notes.
SIMPLE MACHINES
FORCE & MOTION
GRAVITY & INERTIA
NEWTON'S 1ST LAW OF INERTIA
NEWTON'S 2ND LAW: ACCELERATION
NEWTON'S 3RD LAW: ACTION & REACTION
Friday, October 11, 2013
PHYSICS - WORK & POWER
WORK
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In science, the word "work" has a particular meaning.
MEASURING WORK
ACTIVITY I
ACTIVITY QUIZ
ACTIVITY II
ACTIVITY QUIZ II
ACTIVITY III
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In science, the word "work" has a particular meaning.
- Work is done when a force makes an object move.
- Work is only done when the object moves
Work = Force X Distance
W = F d
- Work is done when a force moves an object or changes its direction.
- It is measured in Joules.
- Rule for Work
Work (joules) = Force (newtons) × Distance (meters)
- Example to calculate Work
Question: A weightlifter raises weights of 2000 newtons from the floor to a height of 2 meters. How much work has been done?
Answer:
| Work | = Force × Distance |
| = 2000 N × 2 m | |
| = 4000 J (joules) |
work transfers energy from one object to another & like energy, is measured in joules (J).
One joule equials the work done (and energy transferred) when a force 1 newton (N) moves an object 1 meter in the direction of the force.
Force = mass x acceleration
F = m x a
If this man pushes the box with a force of 100 newtons for 3 meters, he performs _____?
POWER
Power is the rate at which work is done, or energy is transferred. It is measured in watts (W), named after James Watt, and is worked out by dividing the work done by the time taken to do it.
It takes twice as much power to move the box 3 meters in one minute as to move it 3 meters in two minutes.
You can measure how much work you do (in joules) when you go upstairs by measuring the height of the stairs & multiplying it by our weight in newtons (your weight in kilograms x 10).
Divide the work you do by the time it takes to do it to find out how much pwer you exert (in watts). The quicker you go, the more power you exert.
Power is the rate at which work is done, or energy is transferred. It is measured in watts (W), named after James Watt, and is worked out by dividing the work done by the time taken to do it.
Power
- Power is the rate at which work is done. Power is measured in Watts.
- Rule for Power
| Power (watts) = | Work (joules) |
| Time (seconds) |
- Example of calculating Power
Question: A weightlifter lifted 2000 newtons to a height of 2 meters. This was 4000 joules of work. What is the power output if this was done for 2 seconds?
Answer:
| Power = | Work | = | 4000 J | = 2000 W (watts) |
| Time | 2 s |
You can measure how much work you do (in joules) when you go upstairs by measuring the height of the stairs & multiplying it by our weight in newtons (your weight in kilograms x 10).
Divide the work you do by the time it takes to do it to find out how much pwer you exert (in watts). The quicker you go, the more power you exert.
ACTIVITY I
ACTIVITY QUIZ
ACTIVITY II
ACTIVITY QUIZ II
ACTIVITY III
PHYSICS - FORCE & ACCELERATIONS PROBLEMS
Check Your Understanding
1. Determine the accelerations that result when a 12-N net force is applied to a 3-kg object and then to a 6-kg object.
2. A net force of 15 N is exerted on an encyclopedia to cause it to accelerate at a rate of 5 m/s2. Determine the mass of the encyclopedia.
3. Suppose that a sled is accelerating at a rate of 2 m/s2. If the net force is tripled and the mass is doubled, then what is the new acceleration of the sled?
4. Suppose that a sled is accelerating at a rate of 2 m/s2. If the net force is tripled and the mass is halved, then what is the new acceleration of the sled?