CHAPTER 11

Kinematics

IN THIS CHAPTER
Summary: As soon as an object’s velocity changes, you need to analyze the problem using kinematics, which deals with aspects of motion
separate from considerations of mass and force.

Key Ideas
Kinematics problems involve five variables: initial velocity, final velocity, displacement,
acceleration, and time interval.
Use the three kinematics equations whenever acceleration is constant.
Average speed is the total distance in a given time divided by the time it takes you to travel that
distance.
Velocity is just like speed, except it’s a vector.
Acceleration is the change in velocity divided by a time interval.
Displacement is the vector equivalent of distance.
The key rule of projectile motion is that an object’s motion in one dimension does not affect its motion
in any other dimension.

Relevant Equations

The constant-acceleration kinematics equations, which we refer to as the “star” equations:

The equilibrium problems we saw in the last chapter all had something in common: there was no
acceleration. Sure, an object can move at a constant velocity and still be in equilibrium, but as soon as an
object’s velocity changes, you need a new set of tricks to analyze the situation. This is where kinematics
comes in.