Study Guide for Force, Energy, Work and Power, Simple Machines

Study Guide for Energy (KE, PE, Work and Power, Simple Machines, Thermal)
Understand the difference between Kinetic Energy and Potential Energy – identify on a diagram
Unit for energy is Joules
Be able to identify an energy as Kinetic or Potential, based upon a description of a situation
Know how to use the formula KE=1/2mv2 to find kinetic energy, mass, or velocity for objects that are
in motion.
Know how to use the formula for Gravitational Potential Energy GPE=mgh to calculate potential
energy….the potential to move – because it is up high, the potential to fall.
Energy makes things happen. Work is the transfer of energy
LAW OF CONSERVATION OF ENERGY – Energy in a system isn’t lost or created, it just changes forms
Work is, based on the formula W= F d (FORCE MOVING SOMETHING A DISTANCE)
o Remember –If something has not been moved a distance, no work is done.
o Work is the transfer of energy – energy makes things happen
POWER is just simply how fast you do work…related to time…P=W/t
o The faster you do work, the more powerful you are
o Power is measured in Watts (units for power) – think of the lightbulb
Know what mechanical advantage is (both the definition and how to find the value)
o How many times does the machine multiply your force you put in?
o You can calculate by F out(machines force)/F in(force you put in)
Simple machines don’t increase how much work we do, but they do make our work easier by reducing
the amount of force we have to put in or they can do it faster so have more power than us
Inclined planes and levers both give us a mechanical advantage by increasing the distance our force is
applied. Increase the distance for us, decrease the force we need to use W=fd
o Example: work needed is 40J to move an object. If machine puts out a force of 8N and distance
it moves an object is 5m, 8x5=40J of work done…but if the distance we put our force into the
machine (pull a lever down, or push up a ramp) is 10m, then we only need to use 4N of force to
get the same job done.. 4x10=40J of work.
o Ideal Mechanical Advantage of a lever or inclined plane can be calculated just by the shape of
the simple machine itself.
 Input length of lever / output length of lever gives you MA
 Example:
 Length of ramp/ height of ramp gives you MA
 Example:
Know what efficiency of a machine is …No machine is 100% efficient. Work that comes out is always
less than what goes in, because some of your work needs to overcome friction of the machine:
o Example: a Lever helps you lift a large piece of furniture so you can get under it. You put in 50
Joules of work by pushing down 2 meters with 25 N of force. The machine lifted the furniture 1
meter with 45 N of force. Work output was W=fxd W out= 45 x 1 = 45 Joules. You put in 50
Joules W in= 25 x 2 = 50 Joules. Efficiency is 45/50 = .90 = 90%
o Efficiency is Work Output/Work Input x 100
Heat is thermal energy
HEAT MOVES because it is kinetic (moving) energy.
COLD DOES NOT MOVE…it is only the absence of heat, such as darkness being the absence of light
Know the parts of a heating curve, where is the boiling point, where is the melting point?:
 Understand Phase changes – Exothermic
(Freezing, Condensation) and Endothermic (Melting
and Vaporization)
 Know where something is a solid, liquid, or
gas on the curve
 Understand how the kinetic energy of a
substance is different in each state of matter -how
particles are moving…fast in hot things (liquid or
gas), slow in cold things (solid things)
 Understand how the 3 methods of heat
transfer work (conduction, convection, radiation)
 What is temperature…what is it actually a
measurement of? (hint…does not measure how much heat is in a substance)
Why does the temperature stay the same while something is melting or boiling?…see the melting and
boiling points on heating curve above.
What has more heat energy, a red hot penny or a bucket of cool water? A bucket has more heat energy
because there is more matter in a bucket of water…a hot penny cannot make a bucket of water feel
noticeably warmer.
Know difference between the two sources of nuclear energy- Fusion and Fission