Chapter 12
Flash 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.
Output
Force
• MA =
Input force
Efficiency
• Compares the output work to the
input work. Expressed as a percent.
Output
Work
• Efficiency =
x 100%
Input Work
Inclined Plane
• A machine that consists of a flat
sloped surface.
• Ex: ramp
Length of Incline
• MA =
Height of Incline
H
L
Wedge
• A machine that is thick at one
end and tapers to a thin edge at
the other end.
length
of
wedge
W
• MA =
width of wedge
L
Ex: axe, Knife, Teeth
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
1st Class Lever
• A lever that has the fulcrum between the input
(effort) and output (resistance)
E
R
F
• Always changes direction of force. The closer to
the resistance, the more it multiplies your
force.
• Ex: crow bar, see-saw, scissors.
2nd Class Lever
• A lever that has the output force (resistance)
between the input (effort) and fulcrum.
R
E
F
• 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.
3rd Class Lever
• A lever that has the input (effort) between the
output (resistance) and the fulcrum.
R
F
E
• Usually multiplies distance by decreasing the
force.
• Ex: baseball bat, hockey stick, fishing rod.
Wheel and Axle
• A machine that has two circular or
cylindrical objects fastened together
that rotate on a common axis.
radius of the wheel
• MA =
radius of the axle
• Ex: screwdriver, steering wheel, door
knob.
Pulley
• A machine made of a grooved
wheel with a rope.
4 supporting ropes
• MA = the number of supporting
ropes holding the object.
• Ex: flagpoles, cranes, sails.
¼F
1 2 34
Compound Machine
A 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.