# Science Explosion v4, chapter 9

acceleration The change in velocity during a period of time.
block and tackle An arrangement of fixed and movable pulleys connected by ropes.
compound machine A machine that combines two or more simple machines.
distance The amount of space traveled from where an object starts to where it is at any given moment.
effort force The force applied to a simple machine.
fixed pulley A type of pulley that is attached to something so that the pulley does not move; it changes the direction of a force.
friction A force that keeps objects from moving.
fulcrum The fixed point on which a lever turns.
gravity The pull of one object on another.
inclined plane A simple machine consisting of a flat, slanted surface, such as a ramp.
inertia The resistance to a change in motion.
joule The unit used to measure work; equal to one newton meter of work.
lever A simple machine consisting of any bar that turns on a fulcrum.
mechanical advantage The ability to get something moving
mechanical energy The decrease in effort needed to move an object.
momentum The mass and velocity (speed and direction) of an object.
motion Change of an object's position
moveable pulley A type of pulley that moves along a rope where the effort is above the pulley.
newton The unit used to measure force (weight).
pulley Simple machine consisting of a wheel with a chain or rope wrapped in the groove of the wheel.
reference point A fixed, unmoving object needed to determine whether another object has changed position
screw A simple machine consisting of an inclined plane that is wound around a cylinder or cone.
speed The rate at which an object travels; determined by dividing the distance by the amount of time the object takes to travel that distance
velocity The distance an object moves over a given amount of time in a certain direction.
wedge A simple machine consisting of two inclined planes back-to-back.
wheel and axle A simple machine consisting of a wheel and a rod running through the axle.
work A force acting on something and moving it a distance.
Resistance force The force that works against the effort
Machine Any object that makes work easier

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