**Acceleration**

In this lesson...

You will learn how to describe the motion of an object as it accelerates.

You will learn how to calculate acceleration.

**Key Vocabulary:**

acceleration:

change in velocity over time.

accelerate:

speeding up.

decelerate:

slowing down

or negative acceleration.

Constant velocity

: traveling at same speed and direction; zero acceleration

What is acceleration?

it is a

vector

with magnitude and direction

acceleration = change in velocity over time

**Example: Plane Taking Off**

Initial Velocity = 0 m/s

Final Velocity = 40 m/s

Initial Time = 0 s

Final Time = 5 s

**Example: Roller coaster Speeding**

Initial Velocity = 4 m/s

Final Velocity = 22 m/s

Initial Time = 0 s

Final Time = 3 s

**How do you graph acceleration?**

Distance vs. Time Graphs

slope = velocity

Speed vs. Time Graphs

slope = acceleration

**Distance vs. Time Graphs**

**Speed vs. Time Graphs**

Acceleration

measures how much something speeds up or slows down over a period of time.

definition

: the rate at which velocity changes over time.

25

50

0

**In this lesson...**

You will be able to describe what graphs are used to analyze the motion of an accelerating object.

You will be able to describe what graphs are used to analyze the motion of an accelerating object.

0

1

2

3

4

5

1

2

3

4

5

**Example: Car Slowing Down**

Initial Velocity = 25 m/s

Final Velocity = 0 m/s

Initial Time = 0 s

Final Time = 5 s

0 m/s - 25 m/s

5 s - 0 s

=

constant velocity of 200 cm/s, but ZERO acceleration

Example of Acceleration

Velocity

Time

0 mph

0 s

10 mph

20 mph

30 mph

40 mph

1 s

2 s

3 s

4 s

10

10

10

10

acceleration = 10 mph/s East

Velocity can change in three ways:

1. Speed up (accelerate)

2. Slow down (decelerate)

3. Change direction

NorthWest

SouthEast

6 m/s/s

8 m/s/s West

-5 m/s/s

27.2 mph/s

How do you calculate acceleration?

Lamborghini

**Which car has better acceleration?**

0-100 km/h in 2.9 seconds.

0-200 km/h in 9.5 seconds

Ferrari

A bicycle rider increases his speed from 5 m/s to 15 m/s in 10 seconds.

15 - 5

10 - 0

=

1 m/s/s

Vi = ? Ti = ?

Vf = ? Tf = ?

Acceleration =

Vf - Vi

Tf - Ti

Vf = final velocity

Vi = initial velocity

Tf = final time

Ti = initial time

A plane starting from rest is accelerated North to its takeoff velocity of 75 m/s during a 5 second period.

Vf = ? Tf = ?

Vi = ? Ti = ?

75 - 0

5 - 0

=

15 m/s/s

A ball rolling down a hill for 9 seconds accelerates from 3 m/s to 34.5 m/s.

34.5 - 3

9 - 0

=

3.5 m/s/s