Chapter 6 Section 1 Work and Machines

Define work:______________________________________________________________________________________________________________________________What 2 conditions apply to work?1.__________________________________________________________________________________2. __________________________________________________________________________________

• Recall that energy is the ability to cause change.

• Another way to think of energy is that energy is the ability to do work.

• If something has energy, it can transfer energy to another object by doing work on that object.

What does the amount of work depend on?__________________________________________________________________________________________What is the formula for work?

Suppose you push a box of books up a 10m ramp. You apply a force of 10N and it takes you 20s to push the box. How much work is done pushing the box? Remember W=Fd

• Suppose you give a book a push and it slides along a table for a distance of 1 m before it comes to a stop. Did you do work the entire time?

________________________________________________________________________________________________________

What is power?__________________________________________________________________________________What is the formula for power?

NOTICE – The SI unit for power is the Watt (J/s) **Because the watt is a small unit, power often is expressed in kilowatts - One kilowatt (kW) equals 1,000 W

Suppose you push a box of books up a 10m ramp. You apply a force of 10N and it takes you 20s to push the box. How much work is done pushing the box? In the work problem you found that W= 100 JNow use the Power formula to calculate how much power you used. Remember P=W/t

Power and Energy – making connections• Power is also the rate at which

energy is transferred.

• The power involved can be calculated:

NOTICE – Power is Joules/seconds with both work and energy

Suppose a light bulb changes electrical energy into light and heat at a rate of 100J in 2s. How many watts of power does the light bulb have?Use P=E/t

Section CheckSection Check

__________ is the transfer of energy that occurs when a force makes an object move.

A. ConversionB. EnergizationC. PowerD. Work

11Question 1

Section CheckSection Check

The amount of work done depends on what two things?

11Question 2

Section CheckSection Check

Which of the following equations can be used to calculate power?

A. W = F/dB. P =WtC. t = W/PD. P = t/W

11Question 3