Chapter 11 Motion Section 3 Acceleration
Acceleration: the rate at which velocity changes.
Scientifically, Acceleration is described as changes in speed,
changes in direction, or changes in both.
Acceleration is a vector.
An example of acceleration due to change in speed is free fall will discuss later.
Acceleration can be positive  an increasing change in speed
Acceleration can be negative  a decreasing change in speed.
The unit for acceleration is meters per second per second, or
meters per second squared (m/s2).
Free Fall: the movement of an object only because of gravity
Acceleration Due To Gravity (9.8 m/s2): Every second an
object falls in free fall, its velocity increases downward at a rate
of 9.8 meters per second.
Acceleration isn’t always the result of changes in speed. A
horse on a carouse is traveling at a constant speed, but it is
accelerating because its direction is constantly changing.
Sometimes motion is characterized by changes in both speed
and direction at the same time.
Constant Acceleration: the velocity of an object moving in a
straight line changes at a constant rate, this is a steady
change in velocity.
You calculate acceleration for straight-line motion by
dividing the change in velocity by the total time.
a is acceleration, vi is the initial velocity, vf is the final
velocity, and t is the total time.
Change in
velocity
final velocity – initial velocity
Acceleration =
=
Total time
Total time
vf – vi
a=
t
If the velocity increases, then the numerator is positive and
thus the acceleration is also positive.
If the velocity decreases, then the numerator is negative and
the acceleration is also negative.
You can use a graph to calculate acceleration. The slope of a
speed-time graph is acceleration. The slope is change in
speed divided by change in time.
Constant acceleration is represented on a speed-time graph by a
straight line.
Accelerated motion is represented by a curved line on a
distance-time graph.
Linear Graph: a line graph on which the displayed data form
straight-line parts.
In a nonlinear graph a curve connects the data points that
are plotted.
Instantaneous Acceleration: describes how fast a velocity is
changing at a specific instant.