Transcript Physics Review Day 2

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=Fxd
• 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 Transfer
Conduction, 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…