Gr7-Sci 3.2
What is the relationship between input work and output work?
Since machines do not reduce the work you do, your output work can never be greater than your input work.
How does a change in direction make work easier?
Some machines, like pulleys, don't change force or distance. The change the direction of the input force.
How does efficiency affect mechanical advantage?
Because of friction, actual mechanical advantage is always less than ideal mechanical advantage.
What is the formula for efficiency?
Efficiency = (Output Work/Input Work) x 100%
What affect does changing direction have on mechanical advantage?
If only the direction changes, input force will be the same as output force and the mechanical advantage will always be 1.
What is ideal mechanical advantage?
Input distance divided by output distance.
How are input work and output work calculated?
Input work = Input Force x Input Distance; Output work = Output Force x Output Distance
What is mechanical advantage?
It is the number of times a machine increases a force exerted on it.
Name two examples of machines for which the output force is greater than the input force?
Ramp, faucet
How is it possible for output force to be less than input force?
The larger input force must be applied over a shorter distance.
How is it possible for output force to be greater than input force?
The smaller input force must be applied over a greater distance.
mechanical advantage
the ratio of output force to input force
How does a machine make work easier?
A machine makes work easier by changing at least one of the following: the amount of force you exert, the distance over which you exert force, or the direction in which you exert force.
What does a machine do?
A machine makes work easier.
What is an ideal machine?
A machine with an efficiency of 100%
How does friction affect efficiency?
All machines waste some work overcoming the force of friction. The less friction there is, the closer the output work is to the input work.
Do ideal machines exist? Why or why not?
No they do not exist. All machines lose work to friction and so all machines have an efficiency less than 100%
How does increasing distance effect a machine's mechanical advantage?
When a machine increases distance, the output force is less than the input force. The mechanical advantage is less than 1.
When is a machine's mechanical advantage greater than one?
When the output force is greater than the the input force.
efficiency
compares output work to input work and is expressed as a percentage
machine
device that allows you to do work in an easier way
output force
the force exerted on an object by a machine
input force
the force your exert when you do work
