Energy

Energy & Work•Closely related

•Energy: ability to do work

•Work: transfer of energy

• Both measured in Joules

Energy Types1. Kinetic Energy: Energy in

motion

2. Potential Energy: Stored energy (not moving)

• depends on position or condition of object

Examples of KE

Calculating KE

KE = ½ mv2 m = mass v = velocity

• Which increases kinetic energy more: doubling the mass or doubling the velocity?

Examples of PE

FirecrackerBoulder on top of cliff

battery

Elastic Energy(type of potential energy)

• Energy stored in a compressed material– Example: rubber band, spring

Gravitational PE• PE that depends on object’s

height, and weight

G.P.E. = mgh

m = mass g = 9.8 m/s2

h= height.Which will have greater GPE: a rock on a 3 story ledge or a rock on a 20 story ledge?

Forms of Energy•Mechanical Energy: Related to

motion of objects – Ex : moving machine parts

Windmill Engine piston

Mechanical Energy• PE Converts to KE and vice versa

• Mechanical Energy = KE + PE– Total energy

• Skier• Roller Coaster• Dart

Thermal Energy• Related to heat

•Thermal Energy = total KE and PE of all particles in an object– Particles in matter are constantly

moving

Chemical Energy(type of potential energy)

• Energy stored in chemical bonds within a substance

Ex: Gas, food, human body, battery

Electrical Energy• Energy of Electric Charges

Electromagnetic Energy• Energy traveling in the form of

waves

• X-rays Visible light

Nuclear Energy• Energy stored in nucleus of an

atom• Nuclear Power plants convert

nuclear energy to electricity

Energy conversions•Law of conservation of energy:

•Energy cannot be created or destroyed, only converted from one form to another

Impact crater in Arizona formed within past 20 yrsLarge KE of meteor converted to large amount of thermal energy vaporizing everything inClose proximity

Energy conversions•Light bulb : converts electrical into

thermal and electromagnetic energy

•Compressed Spring: converts potential to kinetic

•Burning wood: stored chemical energy converted to thermal and electromagnetic

If friction is ignored total mechanical energy will remain constant

(KE + PE) start = (KE + PE)end

Pendulum would swing forever!!!

Energy Conversion in a Pendulum

Viewing a Pendulum• Pendulum Energy Conversion