1. Energy, Friction & Efficiency

2.  Energy = the ability to do work  When work is done, energy is used  Work is the transfer of energy

3. 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?

4. Which form of energy powers most of our machines?  Thermal (heat)  Electrical  Mechanical (our muscles)  Chemical (gas)  Sound  Elastic  Magnetic  Nuclear  Solar

5.  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)

6. 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?

7. 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

8. 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

9.  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

10. 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

11.  Work done on a machine = work done by the machine + energy lost to friction