Energy, Friction & Efficiency. Energy = the ability to do work When work is done, energy is...

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

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

Energy, Friction & Efficiency. Energy = the ability to do work When work is done, energy is...

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