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Energy
What is Energy?
• Energy is the ability to do work. Any object
that has energy has the ability to create force.
• Energy is one of the fundamental building
blocks of our universe. Energy appears in
different forms, such as motion and heat.
Energy can travel in different ways, such as
light, sound, or electricity.
• Energy is measured in joules, the same units
as work, because energy is stored work. Any
object with energy has the ability to do work.
Forms of Energy
• Mechanical - Mechanical energy is the
energy possessed by an object due to its
motion or its stored energy of position.
Example: simple machines.
• Radiant - Radiant (meaning light) energy is
also known as electromagnetic energy.
Examples: visible light (light we see), x-rays,
heat, and microwaves.
• Sun - Radiant heat from the sun keeps the
Earth warm. We harness the radiant energy
using solar power.
Forms of Energy (2)
• Electrical - Electrical energy is derived
from other sources of energy such
chemical energy from gas, heat energy
from burning the gas, that heat energy
is used to make steam which turns a
turbine to produce mechanical energy,
and the turbine turns an electrical
generator to produce electrical energy.
Forms of Energy (3)
• Chemical - Chemical energy is the type
of energy stored in molecules.
Chemical reactions can either use or
release chemical energy. Examples:
the chemical energy in batteries is
converted to electrical energy and your
body uses chemical energy when it
converts food into energy.
Forms of Energy (4)
• Nuclear Energy - Nuclear energy comes
from splitting an atom (fission), or fusing two
atoms together (fusion). Nuclear energy is
used to generate or make electricity in power
plants (fission). Nuclear energy is really the
basic source for all other energy forms
because it is how the sun and other stars
make energy (fusion).
Forms of Energy (5)
• Thermal Energy – Heat is a form of
thermal energy.
Kinetic Energy
• Energy of a moving object is called
kinetic energy.
Kinetic Energy (2)
• Kinetic energy depends on two things: mass and
speed.
• Kinetic energy increases with speed. Consider a
shopping cart with a certain speed. To make the cart
move faster you need to apply a force to it. Applying
a force means you have to do work. The higher the
speed of the cart, the more energy it has because
you have to do work to increase the speed.
• Kinetic energy increases with mass. If you give the
same cart more mass, you have to push it with more
force to reach the same speed. Increasing the mass
increases the amount of work you have to do to get
the cart moving, so it also increases the energy.
Calculating Kinetic Energy
• Kinetic energy is calculated using the
following equation:
KE (Joules) = ½ m (kg) x v2 (m/s)
Potential Energy
• Potential energy is the stored energy
resulting from the relative position of objects
in a system. Potential energy is basically
stored energy.
• Objects that have potential energy don’t use
their energy until they move. That’s why it is
called potential energy. Potential means that
something is capable of becoming active.
Potential Energy (2)
• Consider a marble that is lifted off a
table. Since Earth’s gravity pulls the
marble down, a force must be applied to
lift it up. Applying a force over a
distance requires doing work, which
gets stored as the potential energy of
the marble. Potential energy of this kind
comes from the presence of gravity.
Calculating Potential Energy
• Potential energy is calculated using
the following equation: PE = wh
Practice
1) A tennis ball with a mass of 51 g has a
velocity of 9.7 m/s upward. What is the
kinetic energy of the tennis ball?
2) What is the potential energy of a rock
that weighs 100 N that is sitting on top
of a hill 300 m high?
Practice
3) A 6.4 kg bowling ball is lifted 2.1 m into
a storage rack. Calculate the increase
in the ball’s gravitational potential
energy.
The Law of Conservation of
Energy
• The law of conservation of energy
states that energy can never be created
or destroyed, just transformed from one
form into another.
Energy Transformations
•
•
•
•
Solar calculator (light to electrical)
Windmill (mechanical to electrical)
Glow stick (chemical to light)
Firecracker (chemical to sound and
light)
• Light bulb (electrical to thermal and
light)
Example of Energy Transformation
• What happens if you throw a ball into the air?
• The ball has kinetic energy when it leaves your hand.
As the ball gets higher it gains potential energy. So
halfway up it has ½ kinetic energy and ½ potential
energy. At the top of its flight the ball stops and has
all potential energy and its speed is zero.
• At any moment in its flight the ball has exactly the
same energy it had at the start. The energy is
divided between kinetic and potential but the total
energy is unchanged.
• Therefore, KE + PE = Total energy