Summary
Displacement is the vector that connects an object’s initial position with its
final position. It is the net distance traveled.
Distance is the length of the particular path chosen (a scalar).
Speed is a scalar quantity and is always taken as a positive.
Velocity is a vector that embodies speed and direction and measures the rate
of change of an object’s position.
Acceleration measures the rate of change of an object’s velocity.
For cases in which acceleration is uniform, use the Big Five equations to find
the missing variable that represents acceleration, displacement, initial
velocity, final velocity, or elapsed time. Memorize the chart on this page.
The two most popular graphs in kinematics are the position-versus-time graph
and the velocity-versus-time graph. The slope of a position-versus-time graph
gives the velocity, while the slope of a velocity-versus-time graph gives the
acceleration.
On a velocity-versus-time graph, the area between the graph and the t-axis is
equal to the object’s displacement.
Gravitational acceleration has a constant magnitude of about 9.8 m/s^2. Use 10
m/s^2 when you estimate.
Since gravitational acceleration is constant, it can be replaced by either +g or
−g with a + sign if down is the positive direction and a − sign if down is the
negative direction. By default, take the direction of an object’s displacement
as positive.
Projectile motion is the parabolic path caused by the pull of gravity on an
object moving near the surface of the earth.
