Transcript How Machines Do Work

Bell Ringer
3-2-10
1. What is the formula for work?
2. What are the units for work?
3. If I pull a rope towards me but it doesn’t move,
is that considered work?
4. Work includes force and motion in the
_______ direction.
Chapter 12 Section 2
How Machines Do Work
 Machines are devices that make it easier to do
work.
 Machines change the way a person does work, not
the amount of work that needs to be done.
How do Machines make work Easier?
1. By changing the amount of force you exert
2. By changing the distance over which you exert
the force
3. By changing the direction in which you exert the
force.
 Input force is the force you exert on a machine.
 The input force moves the machine a certain
distance, called the input distance.
 Input Force x Input Distance = Input Work
 Output force is the force a machine puts on an object.
 The output distance is the distance over which the
machine exerts the force.
 Output force x Output Distance = Output Work
 Mechanical advantage is the number of times a
machine increases a force exerted on it.
 Mechanical advantage = Output force
Input force
 Some machines make work easier by allowing you
to exert a smaller force over a longer distance.
 Other machines allow you to exert your force over a
shorter distance.
 Other machines allow you to change the direction
of input force
 Efficiency is the ability to convert input work to
output work, calculated as:
 Efficiency = output work x 100%
input work
.
 Oil, or another lubricant,
can increase efficiency.
 Friction reduces efficiency by converting some
work into heat.
 The efficiency of a real machine is always less than
100 percent because of friction.