ACCELERATION
Acceleration
is the rate at which velocity changes. Recall that velocity has two
components—direction and speed. Acceleration involves a change in either of these
components. In science, acceleration refers to increasing speed, decreasing speed,
or changing direction.
Any time the speed of an object changes the object experiences acceleration.
That change can be an increase or decrease. A decrease in speed is sometimes called
deceleration, or negative acceleration.
An object that is changing direction is also accelerating even if it is moving at a
constant speed. A car moving around a curve or changing lanes at a constant speed is
accelerating because it is changing direction.
Many objects continuously change direction without changing speed. The simplest
example of this type of motion is circular motion, or motion along a circular path. The
moon accelerates because it is continuously changing direction as it revolves around
Earth.
In summary, acceleration describes the rate at which velocity changes. To
determine the acceleration of an object, you must figure out the change in velocity
during each unit of time. This is calculated by the following formula.
Acceleration = Final velocity—Initial velocity
Time
Copy this formula
onto your index
card!!!
If velocity is measured in meters/second and time is measured in seconds, the
unit of acceleration is meters per second per seconds which is written as m/s2.
EXAMPLE #1:
A man in a boat is travelling at a speed of 15 m/s when it starts to rain. He wants to
avoid getting wet. The boat speeds up to 30 m/s, and it takes 10 seconds to get to
that new speed. What's the acceleration?
C. Bova
1/3/14
EXAMPLE #2:
You are driving your car at a rate of 22 m/s when you come to a dead end in the
road. It takes you 5 s to slow down to 2 m/s. What is your acceleration?
Understanding Main ideas
If the statement is true, write true. If it is false, chance the underlined word or words
to make the statement true.
__________1. If a train is slowing down, it is accelerating.
__________2. To find the acceleration, you must calculate the change in distance
during each unit of time.
__________3. A Ferris wheel turning at a constant speed of 5 m/s is not accelerating.
HOMEWORK
:
1. Before Mr. Bova crashes into a fence, he accelerates on his skateboard along a straight path
from 2.0 m/s to 4.0 m/s in 2.5 seconds. Find his average acceleration.
2. After smashing into the fence, Mr. Bova’s velocity drops from 4.0 m/s to 0 m/s in one second.
Find his average acceleration.
3. Mr. K’s car broke down and he needs to use the subway to get to school. He was traveling
northbound on the subway while listening to his favorite country tunes on his I-pod. The subway
slowed down from 12 m/s to 9.6 m/s in 0.8 s. What’s the acceleration?
4. Mrs. Reilly is trying to catch up to Mrs. Ryan on her bicycle. Initially, Mrs. Reilly was pedaling
at a velocity of 12 m/s. She increases her speed to 16 m/s to catch up. If it takes Mrs. Reilly 3.5
seconds to complete the increase in velocity, what was her acceleration?
C. Bova
1/3/14