Slide 1

Energy and Simple and
Compound Machines

Objective 4.07
Determine how people use simple machines to solve
problems.


Slide 2

• Since a body can do work for different
reasons it can have energy for different
reasons. It is useful to classify energy
according to the reasons that bodies have
it.


Slide 3

Kinetic Energy
• Kinetic energy is the energy of motion.
An object that has motion - whether it is
vertical or horizontal motion - has kinetic
energy. There are many forms of kinetic
energy - vibrational (the energy due to
vibrational motion), rotational (the energy
due to rotational motion), and translational
(the energy due to motion from one
location to another).


Slide 4

Potential Energy
• An object can store energy as the result of its position.
For example, the heavy ball of a demolition machine is
storing energy when it is held at an elevated position.
This stored energy of position is referred to as potential
energy. Similarly, a drawn bow is able to store energy as
the result of its position. When assuming its usual
position (i.e., when not drawn), there is no energy stored
in the bow. Yet when its position is altered from its usual
equilibrium position, the bow is able to store energy by
virtue of its position. This stored energy of position is
referred to as potential energy. Potential energy is the
stored energy of position possessed by an object.


Slide 5

• A cyclist with Kinetic energy is moving up
the hill and transforming the energy into
Potential energy.


Slide 6

Simple and Compound Machines
• The forces at work on simple machines
can be balanced or unbalanced.
Remember, when the forces are balanced,
you can also say that the forces are in
equilibrium.


Slide 7

• Look at the pulley on the left. When the
masses are equal, then the forces on
those masses are balanced. The masses
do not move, and the system is in
equilibrium.


Slide 8

• Now look at the pulley on the right. The
force of 2kg mass is twice that of the force
on the 1kg mass. The forces are not
equal, so the 2kg mass drops and the 1kg
mass rises. The masses will move faster
and faster, so the system is not in
equilibrium.


Slide 9

Fixed Pulleys
• A fixed pulley is a pulley in which the
wheel does not move. Fixed pulleys
change the direction of the effort force. It
does not increase the size of the effort
force. The effort force is equal to the
resistance force in a fixed pulley;
therefore, the mechanical advantage (MA)
of a fixed pulley is equal to 1.


Slide 10

Movable Pulleys
• May be single or combination
• A pulley that moves with the load ( both the load and the
pulley move)
• The load moves in the same direction as the applied
force
• The movable pulley allows the effort to be less than the
weight of the load
• It takes less force to raise an object than if you used only
your hands
• The amount of force required depends on the number of
supporting ropes
• The greater the number of pulleys and supporting ropes,
the smaller the force required.


Slide 11

Compound Machines
• A compound machine is a machine that is
made up of two or more simple machines.
The simple machines in a compound
machine work together to make a task
easier. An example of a compound
machine is a wheelbarrow, which is made
of two simple machines: a lever and wheel
and axle.


Slide 12

• The large machines we are all familiar with are
made up of many simple and compound
machines. Such things would be a car or an
airplane. With all the simple machines working
together, cars and airplanes can overcome the
forces of gravity and moving air. The car
overcomes gravity when it is going up hill, and
an airplane overcomes gravity when it begins a
flight. The engines of the car and airplane
provide the energy the simple and compound
machines need to move the car and airplane.


Slide 13

Review
• Simple machines are used to reduce the
amount of force it takes to do work.
• Compound machines are made of two or
more simple machines.


Slide 14