ENERGY:
CHAPTER 13.3 AND 13.4
PEPS
Rainier Jr/Sr High School
Mr. Taylor
13.3: What is Energy?



Whenever work is done, energy is transformed or
transferred from one system to another system.
Energy has been defined as “the ability to do
work”.
Energy is measured in Joules (the same as work!)
13.3: What is Energy?

Potential Energy vs Kinetic Energy
 Potential
energy is stored energy/ready to work
 Kinetic energy is moving energy/doing work.
13.3: Potential Energy

Potential Energy is stored energy or energy of
position.
 Elastic
potential energy is from compressing or stretching
something.
 Gravitational potential energy is due to differences in
height (h) and depends on the mass of the object (m)
and free-fall acceleration (g)
 GPE
= mgh
13.3: Kinetic Energy

Kinetic energy depends on mass (m) and speed (v)
½ x mass x speedsquared
 KE = ½ mv2
 KE=

Kinetic energy depends more on speed than mass!
13.3: Types of Energy


Mechanical energy: the energy of movement
Chemical energy: energy stored in the chemical bonds
between atoms
 The
energy that is stored in food by photosynthesis is
chemical energy


Nuclear energy is released in a nuclear reaction
Electromagnetic energy is due to the movement of
electrons
 Electromagnetic
space.
energy can be transmitted across empty
13.4: Conservation of Energy

Energy transformations from one form of energy to
another happen easily; the energy of the system
remains the same.
 Potential
energy is transformed to Kinetic energy when
an object accelerates
 Kinetic energy is transformed to potential energy when
an object decelerates.
13.4: Conservation of Energy

The Law of Conservation of Energy states that
energy is neither created nor destroyed in any
system.
 Apparent
loss of energy is actually conversion to
(mostly) non-mechanical forms of energy.
 Acoustic,
thermal, light are common
13.4: Efficiency of Machines

All machines require more work (energy) input than
the useful work (energy) output.
 Friction
and non-mechanical changes of energy are
always present.

Efficiency = (useful work output)÷(work input) x 100%