Energy

What is Energy?

•Energy is the ability to cause change

•Any time you move, or move something you are using energy

Forms of Energy

•What are some forms of energy?

•Electrical – energy in the form of moving electrons

•Chemical – energy from a chemical reaction

•Thermal – energy of heat•Radiant – the energy of electromagnetic

waves including light, gamma rays, microwaves

Converting Energy

•Energy can be converted between it’s different forms

•Radiant Energy is converted to chemical energy through photosynthesis

•Chemical energy is turned into thermal energy in a fire.

•Thermal energy is turned into electrical in a power plant.

•Electrical energy is turned into radiant energy in a lightbulb.

Kinetic Energy

•Kinetic energy is the energy of movement

•KE = ½ mv2

•m is the mass of an object, v is the velocity of an object

•Standard units – kg m2/s2 or Joules (J)

Example•A jogger who’s mass is 60 kg is moving at

3 m/s, what is the jogger’s kinetic energy?•m = 60 kg, v = 3 m/s•KE = 1/2(60kg)(3 m/s)2 = 270 J

Example

•A car moving at a speed of 20 m/s has a KE of 300,000 J. What is the car’s mass?

Example

•A sprinter has a mass of 62.5 kg and a KE of 4000 J. What is the sprinter’s velocity?

Potential Energy

•Potential energy is stored energy

•5 Types of Potential Energy•Elastic•Chemical•Electrical•Nuclear•Gravitational

Elastic

•Elastic Potential Energy is energy stored by something that can stretch or compress

Chemical

•Chemical Potential Energy is the energy stored in the chemical bonds between atoms.

Electrical

•Electrical Potential Energy is the energy due to the position of an electric charge

Nuclear

•Nuclear Potential Energy is the energy stored in the nucleus of an atom

•If you could release all of the nuclear potential energy in you body, you could power the United States for 6 years.

Gravitational

•Gravitational Potential Energy is energy stored due to an object’s position above the Earth’s surface

Formula for Gravitational Potential Energy•PE = mgh•m is the mass of an object, g is the

acceleration due to gravity, h is the height above the Earth

•Standard units – kg m2/s2 or Joules (J)

Example

•A 65 kg rock climber climbs a cliff. What is the climber’s potential energy when she is 35 m above the base of the cliff?

•m=65 kg, h=35m, g=9.8 m/s2

•PE = mgh = (65kg)( 9.8 m/s2)(35m) = 22295 J

Example

•What is the mass of a hiker 200 m above the ground if her GPE is 117600 J?

Example

•Find the height of a baseball with a mass of .15kg and has a GPE of 73.5 J?

Kinetic or Potential

•a moving skateboard, •a rock at the edge of a cliff, •an unconnected battery, •a baseball being pitched, •a gallon of gas, •a stretched rubber band, •a moving car, •a person climbing stairs•a pizza

Energy can change forms

•What happens when you turn on a lightbulb?

•What happens to the lightbulb if you leave it on for a long time?

Conversions •Mechanical energy is the total amount of

kinetic and potential energy in a system.•ME = KE + PE

Law of Conservation of Energy

•Law of Conservation of Energy – energy can not be created or destroyed, only transformed.