Velocity, << vuh LOS uh tee, >> is the rate at which a body moves in space in a given direction. Velocity is expressed in distance and time, such as miles per hour or meters per second.
There is an important difference between speed and velocity. Speed indicates the rate of motion, but it does not indicate anything about the direction of motion. When a body is said to have a speed of 40 miles per hour, the direction is unknown. To specify the velocity, it is necessary to indicate both the rate and the direction of motion. For example, a body may have a velocity of 40 miles per hour toward the north. Mathematically, velocity is a vector quantity, because it has both speed and direction.
Types of velocity.
Velocity may be uniform, which means the distances and the direction traveled during a given unit of time are the same throughout the motion. To find the uniform velocity of a body, we need only divide the distance traveled by the time. This could be stated in the formula v = d/t where v is equal to velocity, d is equal to distance, and t is equal to time.
Velocity may be variable. This means that the distances traveled in a given unit of time are not equal throughout the motion, or that the direction changes, or both. For example, a moving object could have a velocity of 30 meters per second at a certain instant and then speed up to 60 meters per second. If the object gained speed uniformly, its average velocity would equal its initial velocity plus its final velocity divided by two. This could be written Av. v = (v1 + v2)/2 where Av. v represents the average velocity, v1 is equal to the initial velocity and v2 is equal to the final velocity.
Acceleration
is a change in the velocity of a moving body. Positive acceleration means that, during each portion of time, the body moves through a greater distance than during the preceding portion of time. A falling body has a positive acceleration. In negative acceleration, such as a train stopping, a smaller space is traveled in each successive unit of time. Centripetal acceleration occurs when the rate of motion stays the same, but the direction changes.
