Energy

DEFINITION

• the ability to cause a change

• common measurement unit = Joule (J)

FORMS• energy exists in many different forms:

1. potential 2. kinetic3. mechanical4. heat5. chemical6. nuclear7. electrical8. light9. sound

(Gravitational) Potential Energy

• abbreviations: PE, GPE, and PEgravitational

• energy stored in a non-moving object due to its position, shape, or composition in a gravitational field

Kinetic Energy• abbreviation: KE

• energy of motion

• all moving objects have kinetic energy

Mechanical Energy

• total potential energy & kinetic energy of an object

• ME = PE + KE

Heat• Energy that moves from hot objects to cooler

ones

Chemical Energy• energy stored in chemical bonds

Nuclear Energy

• Energy stored in the nucleus of an atom

Electrical Energy

• Energy of moving electrons

Light Energy• Energy contained in electromagnetic waves

Sound Energy

• Energy produced by vibrating objects

Potential Energy Word Problems

A 4 kg rock is sitting on a 3 m ledge.

How much gravitational potential energy does it have?

GIVENS: m = 4 kg h = 3 m g = 9.8m/s2

UNKNOWN: PE

EQUATION: PE = mgh

SUBSTITUTION: PE = (4 kg) x (9.8m/s2) x (3 m)

SOLUTION: 117.6 J

Kinetic Energy Word Problems

A 3 kg ball is rolling at a velocity of 2 m/s.

How much kinetic energy does it have?

GIVENS: m = 3 kg v = 2 m/s

UNKNOWN: KE

EQUATION: KE = ½ mv2

SUBSTITUTION: KE = ½ (3kg)(2m/s)2

SOLUTION: 6kgm/s2 = 6 J

LAW of CONSERVATION of ENERGY

Energy cannot be created or destroyed, BUT

it can be transferred from one object to another

AND it can be changed, or converted, from one

form to another

Energy Transfer

• Occurs when one object passes some of its energy to another object

• First object loses energy; second object gains energy

• 3 main ways: conduction, convection, and radiation

Conduction• Energy is transferred within an object or between objects that are touching

• As particles in objects collide, their energy is transferred

Convection• Fluids (liquids & gases) transport energy from one place to another

• Forms convection currents

Radiation• transfer of energy through electromagnetic waves

• radiation is felt as energy is absorbed by a material

Energy Conversions• AKA energy transformations

• Change of one form of energy into another

example

Electric Fan

• Electrical → kinetic

• When you plug in the fan, electricity causes the blades to move