 Exploring Motion and Forces

Important Vocabulary Speed – The rate of motion, or the rate at which a body changes position. Instantaneous speed – The rate of motion at a given instant in time, such as that given on a car’s speedometer. Constant speed – Speed that does not change. Average speed – A rate of motion determined by dividing the total distance traveled by the total travel time. Velocity – The speed and direction of a moving body, such as a strom or a basketball thrown across a court. 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. Force – A push or a pull one body exerts on another. Unbalanced forces always change the motion of the body. 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. 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. 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. Friction – The force that opposes motion between two surfaces that are touching each other. 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 gravitaional force depends on the masses of the objects and the distance between them. Weight – The measure of the force of gravity on an object. Weight changes with changes in gravity and is measured in newtons (N)

Important Formulas

Calculating Speed

The relationship between distance, speed and time is shown in the equation d = v * t, where d = distance, v = speed, and t = time. If you know the distance and time, you can rewrite the equation as:

d

V = -----             to calculate speed.

T

If the distance and speed are known the formula can be rewriiten as:

d

t = -----               to calculate time.

V

Calculating Acceleration

To calculate average acceleration, divide the change in velocity by the time interval. To find the change in velocity, subtract the initial velocity (starting velocity), v1, from the final velocity, vf.

vf - v1

A = -------------------

t