21 terms

# 4th grade Unit 4 Science - Forces and Motion

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simple machine
one of the basic machines that make up other machines
lever
a simple machine made up of a bar that turns on a fixed point
fulcrum
the fixed point, or point that does not move, on a lever
effort force
the force put on one part of a simple machine, for example, when you push or pull on a lever
work
that which is done on an object when a force moves moves an object through a distance
pulley
a simple machine made up of a rope or chain and a wheel around which the rope or chain fits
wheel and axle
a simple machine made up of a large wheel attached to a smaller wheel or rod
inclined plane
a flat surface with one end higher than the other
efficiency
how well a machine changes effort into useful work
screw
an inclined plane wrapped around a pole
wedge
a machine made of two inclined planes placed back-to-back
position
a certain place
motion
a change of position
frame of reference
the things around you that you can sense and use to describe motion
speed
a measure of an object's change in position during a unit of time; for example, 10 meters per second
force
a push or pull
newton
the metric, or System International(SI) unit of force
acceleration
a change in the speed or direction of an object's motion
gravity
a force that pulls all objects towards each other
weight
a measure of the force of gravity upon an object
friction
a force that keeps objects that are touching each other from sliding past each other easily