Download Energy Friction and Efficiency

Energy, Friction & Efficiency
Energy = the ability to do work
 When work is done, energy is used
 Work is the transfer of energy

The Law of Conservation of Energy

Energy can’t be created or destroyed, it
has to come from somewhere
 What
are some sources of energy?
Which form of energy powers most of
our machines?
 Thermal
(heat)
 Electrical
 Mechanical (our muscles)
 Chemical (gas)
 Sound
 Elastic
 Magnetic
 Nuclear
 Solar
When something is moving it has Kinetic
Energy
 Potential Energy is stored energy due to
position or condition

 Chemical
potential energy: a battery, food, fuel
 Electrical potential energy: a battery
 Gravitational Potential Energy: a skier on top of
hill, a rock on top of hill, water in a dam (hydro
electrical)
For Example

A backhoe lifts the dirt out of a hole
 Work:
moving the dirt upward against the
force of gravity uses:
 chemical
energy (fuel)
 kinetic energy (shovel)

What kind of energy does the dirt have
once it is in the air?
Transmission
Energy can be converted from one form to
anther or it can be transmitted
 Transmission: energy is transferred from one
place to another but no energy is changed or
converted

Ex. bike: energy from one sprocket to another
Ex. electrical wires: from generating station to
house
Friction
Friction is the resistance of motion when
the surfaces of two objects come into
contact
 Friction opposes motion so you will never
get the same amount of work out of a
machine as the effort put in it


The lost work appears as heat or sound

Many machines require very little friction
and need to be lubricated with oil or
grease
Ex. rollerblades, pistons in a car

Some machines depend on friction to
work properly
Ex. erasers, car brakes, parachutes
Efficiency
Efficiency is a comparison of the useful work
provided by a machine to the work supplied to
the machine
 The higher the efficiency, the better the
machine is at transferring energy

Efficiency = work done by a lever on a load x 100%
work done on a lever by effort force

Work done on a machine =
work done by the machine
+ energy lost to friction