"Work, Power, and Simple Machines" Key Terms

This has a couple more terms than listed in the beginning of the packet. I included all terms that are underlined and for which definitions are given in the packet.

work

(W) the amount of energy transferred by a force applied through a finite distance in the direction of the motion

Joule

(J) units of work; 1 Nm

power

(P) the rate of doing work; the rate at which energy is transferred

Watt

(W) units of power; 1 J/s

kilowatt

(kW) 1000 Watts or 10³ Watts

machine

a device for multiplying forces or simply changing the direction of the force; does not make work less

simple machine

a basic machine where we assume efficiency is 100% (ignoring friction losses). Generally refers to the three to six machines identified as classical simple machines

efficiency

ratio of useful work output to total work input; can never exceed 100%

mechanical advantage

(MA) ratio of output force to input force

lever

an arm that pivots or turns against a fulcrum

fulcrum

pivot point of a lever

effort

force applied to a lever

resistance

what a lever is trying to move; also called the load

First Class Lever

the fulcrum is located between the effort and the resistance (This is the one most people think of when they hear the word “lever.”)

Second Class Lever

the resistance is between the effort and the fulcrum

Third Class Lever

the effort is between the load and the fulcrum

inclined plane

a stationary, sloping surface used to raise heavy loads with less effort than lifting straight up

wedge

really just an inclined plane (door stop) or two inclined planes (log splitter) used to lift an object, hold an object, or pry two objects apart

screw

really just an inclined plane wrapped around a cylinder. Used for fastening and also adjusting

wheel and axle

a modified lever consisting of a wheel connected to a rigid pole

pulley

a grooved wheel that turns around an axle; changes the direction of the force (really just a modified wheel and axle)

simple pulley

also called a fixed pulley because it does not move; gains nothing in force, distance, or speed, but changes the direction of the force

movable pulley

free axle pulley; able to move while transferring a load. Depending on the setup, can cause a reduction in effort force and increase in distance

compound pulley

a combination of fixed and movable pulleys

Rube Goldberg

cartoonist who was famous for devising complex ways for doing simple tasks

Pitch

the distance between two consecutive threads on bolts or screws. Often given as threads per inch in the U.S. (thread count). Given as actual pitch in metric bolts (actual distance in millimeters between consecutive threads)

Mechanical Advantage of a Pulley System

number that tells us the ratio of the load to the effort in an ideal pulley system (no friction massless pulleys, etc.)