Physics Review Day 2
Jan 03, 2016
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…