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9Sci CH3
9th Science CH3 Exploring Motion and Forces
| Term | Definition |
|---|---|
| acceleration | the rate of change in velocity (a change in direction or a change in speed); the amount of acceleration depends on velocity change and time interval |
| average speed | a rate of motion determined by dividing the total distance traveled by the total travel time |
| balanced forces | forces that are equal in size and opposite in direction; balanced forces acting on a body do not change the motion of the body |
| constant speed | speed that does not change |
| force | a push or a pull one body exerts on another; unbalanced forces always change the motion of the body |
| friction | the force that opposes motion between two surfaces that are touching one another; the amount of friction depends on the types of surfaces and the kinds of force pressing the surfaces together |
| gravity | force exerted by every object in the universe on every other object; the amount of gravitational force depends on the masses of the objects and the distance between them |
| inertia | the tendency of an object to resist any change in its motion; if motionless, it tends to remain at rest; if moving, it tends to keep moving at the same speed and in the same direction |
| instantaneous speed | the rate of motion at a given instant in time, such as that given on a car’s speedometer |
| net force | the sum of the forces on an object when unbalanced forces are applied to it; a net force changes the object’s speed or direction or both |
| speed | the rate of motion, or the rate at which a body changes position |
| velocity | the speed and direction of a moving body, such as a storm or a basketball thrown across a court |
| weight | the measure of the force of gravity on an object; weight changes with changes in fravity and is measured in newtons (N) |