Physics Review Day 2

Energy

• Energy is conserved in a system, it can not be created or destroyed

• Energy is simply defined as Work

• There are two types:– Potential energy – Kinetic Energy

• Units: Joules, J

Kinetic Energy

• Energy in motion• A increase in velocity causes a great

proportional increase in kinetic energy

• Kinetic Energy = ½(mass x velocity2)

• KE = ½ mv2

• Units: Joules, J

Potential Energy

• Energy Stored by an object• Most important type is Gravitational

Potential Energy

GPE = mass x acceleration of gravity x height

GPE = mgh

Units: Joules, J

Work and Power

Work

• Work is the force applied to something over a distance

• Work = Force x Distance

• W = F x d

• Units: Joule, J

Power

• Power is work done over time

• Power = Work/ time

• P= W/t

• Units: Watts, W

Machines

A device that makes work easier

Simple Machines

• Work is done with only one movement

• 6 basic machines– Lever– Inclined plane– Wedge– Screw– Pulley– Wheel

Compound Machines

• Two or more simple machines are used together

Measuring a Machine’s Efficiency

• For real machines, some of the energy put in is always lost as heat produced by friction; therefore, work output is less then work input

Efficiency = (Work output / work input) x 100

Heat TransferConduction, Convection, and

Radiation

Conduction

• Transfer of thermal energy due to direct contact with a solid

Convection

• Transfer of thermal energy through liquids and gases

Radiation

• Transfer of thermal energy through electromagnetic waves

Electric Circuits

Closed, conducting path that electric charges follow

Circuit Units

• Voltage– The “push” that causes the charge to move– Measured in volts, V

• Current– Flow of the charge– Measured in amperes, A

• Resistance– A material’s tendency to oppose an electric flow– Measured in Ohms, Ω

Ohm’s Law

• Relates electric current, voltage difference, and resistance

• Current = Voltage/ Resistance

• Voltage = Current x Resistance

I = V/R or V = IR

Series Circuit

• Provides only one path for the current to follow (contains only one loop)

• To solve for resistance: – R total = R1 + R2 + R3…

Parallel Circuits

• Current follows more than one path (contains more than 1 loop)

• This is used in houses

• Rtotal = 1/R1 + 1/R2…