# physical science chp. 14

## Terms

copy deck
pulley
a modified lever consisting of a rope that moves around a grooved wheel; can be movable or fixed
distance principle
states that any reduction in the effort force will be paid for by an increased distance through which that force must act
lever
a rigid bar capable of turning about a fulcrum
the amount by which a machine magnifies effort (force)
law of moments
the method for computing the amount of force exerted by levers with unequal arms;
w(1)d(1) = w(2)d(2)
block and tackle
an arrangement of fixed and movable pulleys connected by ropes; has a high mechanical advantage
second-class lever
a lever in which the resistance is located between the fulcrum and the effort
watt (W)
the SI unit of power; 1 joule of energy per second
scientific idealization
approximating an answer when an extremely accurate one is not needed
third-class lever
a lever in which the effort is applied between the fulcrum and the resistance
effort arm
the distance from the fulcrum to the effort
pitch
the distance between two adjacent threads on a screw; how high or low a tone sounds to an observer (related to frequency)
screw
an inclined plane would around a cylinder or cone
inclined plane
a slanted surface used to raise objects
joule (J)
the SI unit of energy; equal to 1 Newton-meter of work
efficiency
the percent of work input returned as useful output
wheel and axle
modified lever in which the effort arm and the resistance arm revolve around a central fulcrum
power
the amount of work done in a given period of time

P = W/t
effort
the force that must be applied to a simple machine to make it produce work
resistance arm
the distance from the fulcrum to the resistance
resistance
the force against which a simple machine works; opposition to the flow of electrons
simple machines
One or two part devices that make work easier: lever, wheel and axle, pulley, inclined plane, wedge, screw
torque
when the law of moments is not being met and there is pivoting on the fulcrum
first-class lever
a lever in which the fulcrum is located between the effort and the resistance
work
the product of the force applied on an object multiplied by the distance the object moved;
w= F x d
fulcrum
the fixed point about which a lever turns
wedge
two inclined planes placed "back-to-back"

27