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force a push or pull
net force when two or more forces act on an object at the same time, the forces combine
balanced forces forces on an object that are equal in size and opposite in direction
unbalanced forces forces on an object that are unequal in size and opposite in direction
inertia tendency of an object to resist any change in its motion
Newton's First Law of Motion if an object is at rest, it stays at rest unless an unbalanced net force acts on it; called law of inertia
Newton's Second Law of Motion the acceleration of an object is in the same direction as the net force on the object
Formula for Force Force = mass x acceleration
friction the force that opposes the sliding motion of two surfaces that are touching each other
air resistance friction like force that opposes the motion of objects that move through the air; depends on speed, size, and shape of an object
Motion an object changes position over time in relation to a reference point
Speed distance an object travels per unit of time; SI unit is meters/second
Velocity includes speed of an object AND the direction of its motion
gravity attractive force between any two objects; depends on the masses of the objects and the distance between them
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