Post on 31-Dec-2015
description
transcript
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.