Law of Conservation of Energy Energy can neither be created nor destroyed It can change forms – Sound becomes mechanical in your ear – Chemical becomes electrical in a battery – Chemical becomes mechanical and heat in your car engine – A chemical energy in a firecracker becomes sound, light, heat, and shock wave

Conservation of Energy I lift a 2 kg book 2 meters into the air As the book is held in the air at 2 meters, it has 40 J of potential energy If I drop the book, it will become 40 J of kinetic energy on the way to the floor

You try it... How much energy does 70 kg person have when an elevator lifts her 20 m into the air? – PE = mgh – PE = (70 kg)(9.8 m/s 2 )(20 m) – PE = J

Continue the problem... What happens to the energy of the same lady when she descends on the elevator to a height of 12 m? – PE = mgh – PE = (70 kg)(9.8 m/s 2 )(12m) – PE = 8232 J – Therefore 5488 J of energy was “lost” – it went into KE as she descended because energy can not be lost!!

How much PE? If the 70 kg person is now 20 m up, how much PE? – PE = mgh – PE = (70 kg)(9.8 m/s 2 )(20 m) – PE = J

What is a machine A machine is something that changes the magnitude (amount) or direction of a force It does not make for less work, only makes the work easier!!

Machines Transform Energy Machines transform energy. Because energy is not created or destroyed – work input = work output Sometimes some of the input is converted to sound or heat due to friction

6 Simple Machines Incline Plane Wedge Screw Lever Pulley Wheel & Axle

This is a ramp The lower the slope, the less force needed The lower the slope, the more distance needed Incline Plane

Wedge This is two incline planes put together An axe, a knife, and the cutting part of scissors are all wedges A wedge will separate material as it pushes through

Screw A screw is an incline plane that is wrapped around a cylinder Screws, bolts, and spiral staircases are all examples

Lever A lever has two parts – The lever (the part that moves) – The fulcrum (the part or location that the lever moves around)

Classes of Levers Three classes of levers – 1 st class – a seesaw – 2 nd class – a wheelbarrow – 3 rd class – a tennis racket

Pulley A single pulley will only change the direction of the force Pulleys may be fixed or moveable A set of pulleys working together is known as block and tackle

Wheel & Axle As the wheel is turned by the effort, the axle will turn with more force A winch and a rear bike tire are examples of wheel and axle

Mechanical Advantage Mechanical Advantage (MA) is a measure of how much the force is multiplied – = force output/ force input