ACCELERATION
When you step on the gas pedal in your car, the car’s speed increases; step on the
brake and the car’s speed decreases. Turn the wheel, and the car’s direction of
motion changes. In all of these cases, the velocity changes. To describe this change
in velocity, we need a new term: acceleration. In the same way that velocity
measures the rate of change of an object’s position, acceleration measures the rate
of change of an object’s velocity. An object’s average acceleration is defined as
follows:
Direct Your Attention to
the Direction
Remember that velocity
has both magnitude and
direction. Acceleration is
a change in velocity over
time, which means that it
measures any change to
the speed and/or direction.
In other words, an object
can maintain a uniform
speed but still have an
acceleration.average acceleration =The units of acceleration are meters per second, per second: [a] = m/s^2. Because
∆v is a vector, ā is also a vector; and because ∆t is a positive scalar, the direction
of ā is the same as the direction of ∆v.
Furthermore, if an object’s original direction of motion is positive, then an increase
in speed corresponds to a positive acceleration, while a decrease in speed
corresponds to a negative acceleration.
A Vocabulary
Speed Trap
The SAT Physics Subject