# Work, Power, Energy.

## Presentation on theme: "Work, Power, Energy."— Presentation transcript:

Work, Power, Energy

Words to define: Work Joule Power Watt Energy Kinetic Energy Potential Energy Machine Fulcrum Pulley Law of Conservation of Energy

Work - amount of energy gained or lost
by an object when a force moves the object through a distance. (W = F x d) Joule - unit of energy. (joule = newton-meter) Power - rate of doing work or transferring energy. Watt – unit of power. (watt = joule/sec)

Energy - ability to do work.
Kinetic Energy – energy due to motion. Potential Energy – stored energy, due to position.

Machine – a device that helps work to be done by multiplying input force at the expense of distance.
Fulcrum – pivot point Pulley – machine that changes the direction of applied force (and often multiplies it too).

Law of Conservation of Energy
energy can not be created or destroyed. It can only change forms.

Work

Work done is defined to as the product of the applied force and the distance through which the object moves.

Work = force x distance Unit: joule = N - m
newton meter Unit: joule = N - m The force is parallel to the direction of motion. Or Distance moved in the direction of the force.

Work is done when an object changes height.
Work is done on an object moved horizontally if there is a force in the direction of motion.

Work can be positive or negative.
If force and displacement are in the same direction, the work done is positive. If force and displacement are in opposite directions, the work done is negative.

The work done on an object equals the change in energy of the object.
W = DE

Find the amount of work done by a weightlifter in lifting a 100 kg barbell a distance of 3 meters.
W= F x d = 100 kg x 10 m/s2 x 3 m = 3000 N-m = 3000 J

A golf cart moves to the right. The driver applies the brakes
A golf cart moves to the right. The driver applies the brakes. And stops the cart in 5 m. A constant braking force of 900 N is applied over this distance. What is the direction of the braking force? How much work is done on the cart by this force? The braking force acts to the left. W = F x d = - 900N x 5m = N-m = J

In the absence of friction, all work should be the same regardless of path taken.