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
