Chapter 12Flash Cards

20 index cards

Work• When force is exerted on an

object causing it to move in the same direction• Work = F x D• Joule (J) = N•m

Joule• The amount of work you do when

you apply a force of 1N to move an object 1m. • 1N•m = 1J

Power• The amount of work done on an

object in a unit of time• Power = Work/Time J/s• Unit is the Watt (W)

Machine• A device that makes work easier

by changing the amount of force you exert, the distance over which you exert the force, or the direction in which you exert the force.

Input Force• The force you exert on a

machine. • Also called effort.

Output Force• The force that the machine exerts

on an object. • Also called resistance.

Input Work• The input force times the input

distance.

Output Work• Output Force x Output

Distance• Always less than Input Work

Mechanical Advantage• The Number of times a machine

multiplies your input force.

• MA =

Output ForceInput force

Efficiency • Compares the output work to the

input work. Expressed as a percent.

• Efficiency = x 100%Output WorkInput Work

Inclined Plane• A machine that consists of a flat

sloped surface. • Ex: ramp

• MA =

H L

Length of InclineHeight of Incline

Wedge• A machine that is thick at one

end and tapers to a thin edge at the other end. • MA = W

L Ex: axe, Knife, Teeth

length of wedgewidth of wedge

Screw• An inclined plane wrapped

around a cylinder.

• MA increases as the threads get closer together.

• Ex: jar lid, car jack.

Fulcrum and Lever• A lever is a rigid bar that pivots or

rotates on a fulcrum. • A Fulcrum is a fixed point for a lever

to pivot on.

Fulcrum

Lever

1st Class Lever

• A lever that has the fulcrum between the input (effort) and output (resistance)

• Always changes direction of force. The closer to the resistance, the more it multiplies your force.

• Ex: crow bar, see-saw, scissors.

F

E R

2nd Class Lever

• A lever that has the output force (resistance) between the input (effort) and fulcrum.

• Input and output forces are in the same direction. The closer the output is to the fulcrum, the more MA you get.

• Ex: Door, wheel barrow, nutcracker.

F

R

E

3rd Class Lever

• A lever that has the input (effort) between the output (resistance) and the fulcrum.

• Usually multiplies distance by decreasing the force.

• Ex: baseball bat, hockey stick, fishing rod.

F

R

E

Wheel and Axle• A machine that has two circular or

cylindrical objects fastened together that rotate on a common axis.

• MA =

• Ex: screwdriver, steering wheel, door knob.

radius of the wheelradius of the axle

Pulley• A machine made of a grooved

wheel with a rope.

• MA = the number of supporting

ropes holding the object. • Ex: flagpoles, cranes, sails.

4 supporting ropes 1 2 3 4

¼ F

Compound MachineA machine that utilizes (makes use of) two or more simple machines.

MA is the product (multiply) of the MA of the machines that make it up. Ex: can opener, apple peeler.