Transcript Kinetic and Potential Energy Conservation of Energy

Kinetic and Potential Energy
Conservation of Energy
Kinetic Energy
kinetic energy - the energy objects
have because they are in motion
m –mass of object (kg)
v – velocity of object (m/s)
Example
A 1400 kg car is travelling at 30 m/s. What
is its kinetic energy?
Potential Energy
 Potential energy - energy an object has because of its
position or state. (stored work)
 Use the symbol U to represent potential energy.
 A battery contains chemical potential energy and when
that energy is released, it can do work to power your
walkman, etc.
Gravitational Potential Energy
The potential energy used most often in
physics is gravitational potential energy.
When you lift a bowling ball, you must do
work against gravity. That work is
transformed into gravitational potential
energy which can be released as kinetic
energy if you drop the ball.
Formula for PE
 To eliminate the
choosing of a
reference point we
talk about change in
potential energy
Example
What is the increase in the gravitational
energy of a 5 kg book that is lifted from the
floor to a table 1.5 m high?
Example 2
A falling ball of mass 250 g losses 25 J of
gravitational potential energy. What
distance has the ball fallen?
Potential Energy of a Spring
You can also store potential energy in a
spring. The formula for this is:
Us = ½kx2
Notice that it's the same formula as the
work done by a spring. Also notice that
spring potential energy is always positive.
Displacement and PE
Energy and Conservation
 One of the most fundamental and powerful ideas
in physics is the one of energy conservation.
 the total mechanical energy of a system is
conserved. That is, the energy it initially has
must be equal to its final energy.
 mechanical energy=the sum of its kinetic and
potential energies.
Energy Conservation
You can write the conservation of energy
statement in many different mathematical
forms. Here are some of them:
KEi + PEi = KEf + PEf