Mechanical Advantage- force output/ force input; how much a machine multiplies ... Friction- What opposes motion; this is why machines are not 100% efficient.
Name:_______________________ Date:_______________________ Period:_____

Chapter 8 Test Review Guide Please complete on a SEPARATE SHEET of paper

Use the following words in a sentence that demonstrates the meaning of the word as we have learned it: Vocab:

Force- a push or a pull. It can be observed on object if the object moves

Work- work= force x distance; a force being applied over a distance

Power- Power=work/time; How much work is done in a certain amount of time

Joule- the unit we use to measure work

Watt- the unit we use to measure power

Mechanical Efficiency- work output/work input x 100%; How efficient a machine is

Mechanical Advantage- force output/ force input; how much a machine multiplies your input force

Input Work- What you physically do to a machine

Output Work- What the machine does to the object

Machine-anything that we use to make work easier

Friction- What opposes motion; this is why machines are not 100% efficient

Inclined Plane- a ramp; it makes work easier by increasing the distance which the object must travel

Wheel and Axle- an axle surrounded by a larger wheel; makes work easier

Lever- a straight bar that makes work easier by pivoting around a point

Fulcrum- a fixed point that a lever pivots around

Pulley- a grooved wheel with a rope or chain running through it to make work easier

Screw- a cylinder wrapped with an inclined plane

Wedge- two inclined planes back to back usually used to cut things

Complex Machine- a combination of 2 or more simple machines

Provide an answer for each of the following questions: ← Describe a real life situation where force and motion are occurring but no work is being done. Work NOT bring done: carrying a backpack home (no work b/c force and motion are not in the same direction) ← Describe a real life situation where work is being done. Work being done: picking up a backpack off the floor (force and motion are in the same direction) ← State and be able to use the formula used to calculate work. Work = force x distance (distance must be in meter) ← State and be able to use the formula for power. Power = work/time (time must be in seconds) ← How can power be increased? You can increase power in two ways: 1. do more work in the same amount of time 2. do the same work in less time ← Can a machine ever be 100% efficient? Why or why not? A machine can never be 100% efficient because all machines have moving parts that generate friction. Therefore, some work input must be used to overcome friction ← State an example AND the advantage of the following machines: fixed pulley, wheel and axle, inclined plane, wedge and screw. *Fixed pulley: ex. flagpole or blinds, this machine makes work easier by changing the direction of the input force *Wheel and axle: ex. door knob, this machine makes work easier by allowing you to use less force over a greater distance *Inclined plane: ex. ramp or slide, this machine makes work easier by allowing you to use less input force over a greater distance *Wedge: ex. knife, this machine makes work easier by allowing you to use less input force over a greater distance *Screw: ex. jar lid, this machine makes work easier by allowing you to use less input force over a greater distance ← Draw a real life example of a 1st, 2nd, and 3rd class lever. Then label the effort force, fulcrum and load or resistance force for each lever. * 1st class lever: the fulcrum is between the effort (input force) and the load (resistance force). This lever makes work easier by changing the direction of the input force. Ex: see-saw *2nd class lever: the load(resistance) is between the fulcrum and the effort(input) force. This lever makes work easier by allowing you to use less input force over a greater distance. ex: wheelbarrow *3rd class lever: the effort is between the load (resistance) and the fulcrum. This machine makes work easier by ,multiplying your input distance (meaning input force is greater). ex: baseball bat, hockey stick

← Label as many simple machines as you see in the following diagram:

[pic] wheel and axle: tires, steering wheel inclined plane: windshield lever: windshield wipers, door

Chapter Review Questions: ← p. 232-233 # 4-11, 14, 18, 19, 23 and 24