11/23/09
Post date: Nov 23, 2009 2:39:54 PM
Bell Ringer: In science what does it mean to say that energy is conserved?
Review ch. 13 material
Work
W = Fd
Amount of energy used to move something
force and motion must be in same direction
measured in J
Power
P = W / t (work divided by time)
Amount of energy changing forms in a certain time period
measured in watts
Mechanical Advantage
MA = output force / input force
MA = input distance / output distance
Ratio that describes how much a machine changes the force you put in
Machines with large MA amplify a force greatly
Simple Machines
Lever Family
Simple Lever
Pulley
Wheel and axle
Inclined plane family
Simple inclined plane
Wedge
Screw
When simple machines are connected together, we call it a complex machine.
Energy
Energy is ability to do work
Measure in Joules (J)
Potential Energy
energy of position, caused by gravity
PE = mgh
Kinetic Energy
energy of motion
KE = 1/2 m v^2
Other forms of energy
heat
light
sound
electro-magnetic
chemical
nuclear
Conservation of energy
Energy can neither be created nor destroyed, but it changes forms readily
Efficiency
Percent of energy transferred from one form to another
efficiency = (useful energy output) / (energy input)
Efficiency is always less than 100%, some energy always goes to heat due to friction
Chapter 13 review game
Chapter 13 review assignment
Page 466-467: 1-25 (pick 15 for credit, more for extra credit)
Due tomorrow