Potential energy is the energy stored in an object due to its position or state. Kinetic energy is the energy of motion. When an object moves, its potential energy is converted to kinetic energy. For example, when a ball is thrown upwards, it has maximum kinetic energy when moving fastest and maximum potential energy when stopped at the highest point. As it falls, potential energy is transferred back to kinetic energy. Similarly, water at the top of a dam has potential energy that is converted to kinetic energy as it falls, powering generators to produce electricity. In a closed system, the total mechanical energy, the sum of potential and kinetic energy, remains constant as one form is converted to the other.

1. Potential Energy
•It’s the energy that is stored because of an object’s
position.
•The Higher an object is lifted above earth, the greater is
it’s potential energy

3. Converting potential and
kinetic energy

4. When you throw a
ball upwards it is
moving the fastest
so it has maximum
kinetic energy
As the ball moves
upward , it slows
down and stops
for an instant
As the ball moves
downward it
speeds up and the
potential energy is
transferred into
kinetic energy

7. Energy changes in falling water
Is converted
to

8. Water at the top of the dam has
potential energy.
When water falls downwards
the potential energy changes
into kinetic energy
The kinetic energy
in the moving
water spins the
generators and
that’ll produce
electrical energy

9. KE and PE
• In many situations, there is a conversion between
potential and kinetic energy.
• The total amount of potential and kinetic energy in a
system is called the mechanical energy
• Mechanical energy = PE + KE

10. Mechanical Energy
•The mechanical energy does not change because the loss
in potential energy is simply transferred into kinetic
energy.
•The energy in the system remains constant!!

11. Mechanical Energy
The energy of movement.
This energy includes both
kinetic energy (motion) and
potential (stored) energy

12. Mechanical Energy
• Mechanical energy is due to the position and
motion of the object.
• What happens to the mechanical energy of
an apple as it falls from a tree?

13. Mechanical Energy
•As the apple falls to the ground, its height decreases.
Therefore, its PE decreases.
•The potential energy is not lost… it is converted into
kinetic energy as the velocity of the apple increases.
•What happens to the mechanical energy?

14. Swinging Along
•Think about the changes in energy when you are on
a swing…
•At what point do you have the most potential
energy?
•At what point do you have the most kinetic energy?
•What happens to the mechanical energy?