Chapter 4 Work and Machines

Which class of lever does not multiply the input force? What is its advantage?

third class. it multiplies the distance of the input force

A simple machine that might be thought of as an inclined plane that moves is a

wedge

Most machines in your body, which consist of bones and muscles, are

wedges

The mechanical advantage of a machine that changes the direction of force only is

1

An ideal machine would have an efficiency of

100 %

If you exert a force of 20 newtons to push a desk 10 meters, how much work do you do on the desk?

200 joules

If you exert a force of 20 newtons on a can opener, and the opener exerts a force of 60 newtons on the can, the ideal mechanical advantage of the can opener is

3

One example of a compound machine is a

bicycle

What do machines do?

change force or distance

Pulling down on a rope to hoist a sail on a sailboat is an example of a machine?

changing direction

A machine that utilizes two or more simple machines is called a

compound machine

The ideal mechanical advantage for an inclined plane is equal to the length of the incline divided by the

height of the incline

In order to do work on an object, the force you exert must be

in the same direction as the object's motion

Which body parts are shaped like wedges?

incisors

A ramp is an example of a simple machine called a(n)

inclined plane

How can a hockey stick be considered a machine?

it multiplies distance

Which body parts act as the fulcrums of levers?

joints

Work is measured in

joules

If tight scissors have an efficiency of 50 percent, how much of your work is wasted overcoming friction?

one half

The efficiency of a machine compares

output work to input work

When you raise or lower a flag on a flagpole, you are using a

pulley

Which of these is an example of work being done on an object?

pushing a child on a swing

The ideal mechanical advantage of a wheel and axle is equal to the

radius of the wheel divided by the radius of the axle

A term that means the same thing as output force is

resistance force

Which of these could be considered an inclined plane wrapped around a cyclinder?

screw

A device with toothed wheels that fit into one another is called a

system of gears

For work to be done on an object, such as pushing a child on a swing,

the object must move some distances as a result of a force

The fixed point that a lever pivots around is called the

fulcrum

work=force *

distance

without friction there would be

equal input and output work

In what class of lever is the direction of the input force opposite to the direction of the output force?

first class

What class of lever is a pair of scissors? Explain your answer?

first class because the fulcrum is between the input force and the output force

Which of these is an example of a third-class lever

fishing pole