Bell Ringer 4-9-10

1. What is kinetic energy?2. What is potential energy?3. What SI unit measures energy?4. 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.