Right side

Vocabulary

work-

joule-

1. Meaning of work

A. You do work on an object when
you exert a force on an object that causes the object to move some distance.

B. fig. 1, pg. 98

2. No work without motion

A. In order for you to do work on
an object the object must move some distance as a result of your force.

B. In order to do work on an object
the force you exert must be in teh same direction as the objects motion.

3. Calculating work

A. the amount of work done on an
object can be determined by multiplying force times distance

B. formula

work = force x
distance

Summary

Left side

practic problems pg. 100

Ch 4 – 2 Mechanical Advantage and Efficiency

Right side

Vocabulary

input force-

output force-

machine –

ideal mechanical advantage -

actual mechanical advantage -

1.What is a machine?

A. Something that makes work easier on you.

B. How?

1. Changes the amount of force
you exert

2. The distance over which you
exert your force

3. Or the direction in which
you exert your force

2.Forces

A. Input – the force you exert

B. Output – the force exerted by the machine

3. Multiplying force – read paragraph on page 103

4.Multiplying distance – read paragraph on pg. 104

5.Changing direction – read paragraph on pg. 104

6.Mechanical Advantage

A. Number of times a force exerted on a machine
is multiplied by the machine.

B. Formula

mechanical advantage = output force

input force

7.Efficiency

A. Compares the output work to the input work

B. Expressed (written) as a percent

C. Higher the percent – the more efficient the machine
is.

8.Calculating efficiency

A. Divide the output work by the input work and
multiply the result by 100 percent

B. Formula

Efficiency = output work x 100%

input work

________________________________

Summary -

Left Side-

Practice Problems (page 106)

1. You cut the lawn with a hand lawn mower. You do 250,000 J of work
to move the mower. If the work done by the mower in cutting the lawn
is 200,000 J, what is the efficiency of the lawn mower?

2. You do 1,500 J of work in using a hammer. The hammer does 825 J
of work on a nail. What is the efficiency of the hammer?

3. Suppose you left your lawn mower outdoors all winter. It’s now rusty.
Of your 250,000 J of work, only 100,000 go to cutting the lawn. What
is the efficiency of the lawn mower now?

Chapter 5 section 4 Power

Right side

Vocabulary

power-

1. Calculating power

A. Power is calculated by dividing
the amount of work done by the amount of time taken to do the work.

B. formula

power = work/time

C. Units

Watts

D. Since work is equal to force times
distance you can rewrite the equation for power as follows:

power = force x
distance/time

E. Units

1. 1 watt
= 1 J/s

2. Power and energy

A. Power is the rate at which energy
is transferred from one object to another or converted from one form to another.

B. read pg. 152-153

Summary

Left side

practice problems pg. 151