chapter 12 flash cards 20 index cards. work when force is exerted on an object causing it to move in...
TRANSCRIPT
Work• When force is exerted on an
object causing it to move in the same direction• Work = F x D• Joule (J) = N•m
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.
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