Workand

Power

What is “Work”?

• When an object actually moves in the same direction as a force.

Force

The movement of Homer in the same direction as the force that pushed

him means that some work was accomplished!

Formula for Work

Ns

mkgonacceleratimassForce

][

][2

Js

mkgDistanceForceWork

][

][2

2

Work is measured in a unit called “Joules”

Ungh!This is HARD

WORK!

Whe-hewThis is FUN!

Force(Push)

Distance

WorkA push or pull can always be applied,

but its not until we actually move it that the person did work on the object.

Think: If no movement occurs, was any work actually done?

Js

mkgDistanceForceWork

][

][2

2

If we apply a force of 100 N, but the object doesn’t move, how

much work was done?

100 N x O m = ? W

Work is when a force moves an object

Here’s the point: Work is what was actually accomplished!

Main Concept 1:

• Work is only done when the force and motion are in the same direction .

The elevator is creating a force that moves the container up. The force and movement is the work that the elevator has accomplished.

What is “Power”?

• We like to think of Power

as how strong someone is

• But in science we use

“power” to say how long it

takes to do a certain

amount of work

OR

Here’s the point:Both will get the same work done (cutting all the boards),

but one will take less time = more power!!!

More or Less Power?

So here we have a certain amount of stacked wood. We need to cut it!

We have several choices of tools we can use:

Hand Saw

“Power Saw”

It’s nice to get work done quickly!

Since this saw does the same work faster than the hand

saw, we say it has MORE POWER!!!

This saw will get the workdone eventually, but it takes

way too long to do it

Main Concept 2: Power is ONLY about how fast

work gets done!

Formula for Power

Js

mkgDistanceForceWork

][

][2

2

WattWs

J

Time

WorkPower ][

][

][

Power is measured in a unit called “Watts”

Ungh!Need… more…

POWER!

Gee … Isn’t he just mighty powerful?

Force(Push)

Distance

Power

Time [s]

Once work is calculated, we simply see how much time we actually moved someone/something.

Once we find our unit rate of how much work we did in 1 second, we’ve found out how much

“Power” we exerted.

What is “Effort”?

• While there are more technical definitions, we can think of effort as how hard it is to accomplish work.

Which takes LESS effort to move with:Walking or Riding?

Usually, riding on a moving object takes less energy than walking the same distance.

So, riding on a skateboard takes less effort to move than just walking.

Effort is really the whole point of this entire unit! Humans like things to be as easy

as possible. So we want to learn how to do work with as little effort as possible!