# Kinematics

By Levi Clancy for Student Reader on
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vf = vi + a t

xf = xi + ½ ( vi + vf ) t

xf = xi + vi t + ½ a t2

vf2 = vi2 + 2 a ( xf - xi )

TermDescription

Freefall

A freely falling object moves freely under the influence of gravity alone. When air resistance is ignored (a vaccuum is a simplification model) then the object is in free fall. Magnitude of free-fall acceleration is denoted by g. At the surface of Earth, g is approximatel 9.80 m/s², or 980 cm/s², or 32 ft/s². It can be assumed that the vector g is directed toward the center of Earth. Important Note: if you throw up a ball with a certain vi, and you thrown down a ball with the same vi, they will both have the same velocity when they hit the ground.

Uniform Circular Motion

In uniform circular motion, a particle moves in a circle at constant speed. However, the acceleration is constantly changing. This is because acceleration is a change in velocity, the velocity vector is changing direction. The acceleration vector is always perpindicular to the path and always points toward the center of te circle. This is centripetal acceleration, and its magnitude is defined by the equation below. r represents the radius of the circle. The subscript on the acceleration symbol means that the acceleration is centripetal.

ac = vÂ²/r