Bell Ringer
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4-9-10
What is kinetic energy?
What is potential energy?
What SI unit measures energy?
Do you think energy can be lost during a transfer of
energy? Explain.
Chapter 13 Section 3
Energy Transformations
Energy
Transformation
• Most forms of energy can be transformed into
other forms.
• A change from one form to another is called
energy transformation.
Single
Transformations
• Toaster - electrical energy  thermal energy (to toast your bread)
• Cell phone - electrical energy  electromagnetic energy (that travels to
other phones)
• Human body - chemical energy in your food  mechanical energy you
need to move your muscles and  thermal energy to maintain body
temperature
More Examples
• A steam iron
__________ energy __________ energy
• A ceiling fan
__________ energy __________ energy and ___________
energy
• A hair dryer
__________ energy __________ energy and ___________
energy
Multiple
Transformations
• The mechanical energy used to strike a match is transformed first to
thermal energy.
• The thermal energy causes the particles in the match to release stored
chemical energy, which is transformed to thermal energy.
• The light that you see is electromagnetic energy.
Another Example
• In a car, electrical energy produces a spark.
• The thermal energy of the spark releases chemical energy in the
fuel.
• The fuel’s chemical energy in turn becomes thermal energy.
• Thermal energy is converted to mechanical energy to move the
car and electrical energy to produce more sparks.
Another Example
• Using coal to power a generator: Chemical Energy is
converted to heat energy (steam) which is converted to
mechanical energy (turns blades of turbine) to electrical
energy and then back to heat energy (using a toaster at
home).
• One of the most common transformations is between
potential and kinetic energy.
• Potential Energy  Kinetic Energy
Examples of
Potential  Kinetic
1. Juggling
2. Pendulum
3. Pole Vault
Conservation of Energy
• The law of conservation of energy states that when one form of
energy is transformed to another, no energy is destroyed in the
process.
• Energy cannot be created or destroyed.
• Total Amount of energy is constant!!!!
Energy Efficiency
• Energy efficiency is how much useful energy you can
get out of a system.
• In theory, a 100% energy-efficient machine would
change all of the energy put in it into useful work.
Examples of
Efficiency
• The human body is less than 5% efficient….most energy
is transferred to heat energy.
• An incandescent light bulb converts 10% of electrical
energy into light and the rest is converted into thermal
energy.
• Electrical Power plants are about 35% efficient.
Heat
• During these transformations some energy may be
released in the form of heat (friction).
• No machine is 100% efficient because friction
transforms mechanical energy to thermal energy.