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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 anotherEx. 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 properlyEx. 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