## Friday, October 11, 2013

### PHYSICS - WORK & POWER

WORK
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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?

 Work = Force × Distance = 2000 N × 2 m = 4000 J (joules)
MEASURING WORK
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.

# 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?

 Power = Work = 4000 J = 2000 W (watts) Time 2 s

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.

ACTIVITY I

ACTIVITY QUIZ

ACTIVITY II

ACTIVITY QUIZ II

ACTIVITY III