Unit 3: Acceleration

Chapter 4 Part 2

Acceleration

Review: Position v Time Graphs

Multiple Choice

If an object was speeding up, what would the graph look like?

• A flat line

• A constant positive line

• A constant negative line

• A changing positive line

Multiple Choice

If an object was NOT moving, what would the position v time graph look like?

• A flat line

• A constant positive line

• A constant negative line

• A changing positive line

Example of Position v Time Graph:

Multiple Choice

What was the total displacement?

• 2 m

• 1 m

• 4 m

• 3 m

Multiple Choice

What was the total distance?

• 21 m

• 12 m

• 8 m

• 3 m

Example of Position v Time Graph:

Multiple Select

Position v Time graphs help us determine...

• average time

• average acceleration

• average speed

• average velocity

Acceleration

Rate of change in velocity of an object
Formula: Change in velocity/change in time

Units: cm/ sec²

Remember- since you are considering
velocity, if direction changes, you have
acceleration

Acceleration

Occurs when

● You speed up
● You slow down
● You change direction

Acceleration can be positive or negative
0 acceleration- traveling at a constant rate or
stopped

Acceleration Formula

Multiple Select

0 acceleration means...

• you speed up

• you slow down

• you have a constant speed

• you are stopped

Example calculation #1

A car goes from 0mi/hr- 30mi/hr in 5
seconds. What is its acceleration?

Multiple Choice

What did you get?

• 5 mi/hr2

• 6 mi/hr

• 6 mi/hr/sec

• 10 mi/hr2

Example calculation #1

A car goes from 0mi/hr- 30mi/hr in 5
seconds. What is its acceleration?

Example calculation #2

A car slows to a stop from 45 mi/hr in 3
seconds. What is the acceleration?

Multiple Choice

What did you get?

• 15 mi/hr2

• -15 mi/hr/s

• -30 mi/hr2

• -15 mi/hr2

Example calculation #2

A car slows to a stop from 45 mi/hr in 3
seconds. What is the acceleration?

Example Calculation #3

How much time did it take for a car speed
up from 15-45 mi/hr if there is an acceleration of 5mi/hr²?

Multiple Choice

What did you get?

• 10 sec

• 5 hr

• 6 hr

• -6 sec

Example Calculation #3

How much time did it take for a car speed
up from 15-45 mi/hr if there is an acceleration of 5mi/hr²?

Graphical Analysis

Conclusion from both labs

For the car and ramp lab, the car is gaining
velocity as it travels down the ramp

On a position vs. time graph, this result shows a curve

Why? Slope is velocity, which is changing

On a velocity vs time graph, this result shows a straight
line

Why? Slope is acceleration, which is not changing

Velocity Time Graphs

● Like a speedometer
● Gives us speed AND direction, NOT position!!

Multiple Choice

What does the line from 0 to 14 seconds tell us?

• stopped

• constant positive velocity

• positive acceleration (speeding up)

• negative acceleration (slowing down)

Multiple Choice

What does the line from 14 to 44 seconds tell us?

• stopped

• constant positive velocity

• positive acceleration (speeding up)

• negative acceleration (slowing down)

Multiple Choice

What does the line from 44 to 54 seconds tell us?

• stopped

• constant positive velocity

• positive acceleration (speeding up)

• negative acceleration (slowing down)

Multiple Choice

What does the line from 54 to 60 seconds tell us?

• stopped

• constant positive velocity

• positive acceleration (speeding up)

• negative acceleration (slowing down)

Velocity vs. Time Graphs

Find slope- the units you get are cm/sec²

In other words, slope of a speed vs time graph is
acceleration

Interpreting a velocity time graph

Multiple Choice

What's happening from A to B?

• at rest

• constant velocity

• increasing velocity

• decreasing velocity

Interpreting a velocity time graph

Multiple Select

What's happening from B to C?

• at rest

• constant velocity

• increasing velocity

• decreasing velocity

Interpreting a velocity time graph

Multiple Choice

What's happening from E to F?

• at rest

• constant velocity

• increasing velocity

• decreasing velocity

Interpreting a velocity time graph

Guidelines for Interpreting Velocity vs. Time Graphs

You must remember that the slope of this
graph is acceleration

If the slope is a straight line, then the object has a
constant acceleration

No slope means that the object has no acceleration NOT
that it is always stopped

A constant acceleration is a change in velocity, and that
change is by the same increment for every unit of time

Summary of Position Time vs. Velocity Time Lines

If position time graph looks like the following, then the velocity time graph will look
like the following

Guidelines for Position vs. Time Graphs

A slope means that the object has velocity

If the line is straight, then the velocity is constant
(no acceleration)

If the line is curved, then the velocity changes (an
acceleration)

If no slope, then the object is stopped

How to Convert Position vs. Time to Velocity vs. Time

Step one: Look at the slope of the position vs
time graph


If the slope is a straight line, then the velocity vs time
graph should NOT have a slope



Step two: Calculate the slope of the position vs.
time graph to know where to position the line
on the velocity vs time graph

Summary of Position Time vs. Velocity Time Lines

If position time graph looks like the following, then the velocity time graph will look
like the following

Velocity vs. Time Graphs Continued

To calculate distance traveled on a velocity
vs. time graph
Find the area under the line
This is accomplished by sectioning off the graph into
shapes
Find the area of each shape
Add the areas together

Example

Multiple Choice

What is the area under section A?

• 50

• 25

• 10

• 5

Example

Multiple Choice

What is the area under B?

• 125

• 50

• 150

• 100

Example

Multiple Choice

What is the area under C?

• 75

• 50

• 100

• 25

Multiple Choice

What is my total area under the line?

• 100 m

• 150 m

• 200 m

• 250 m

Free Fall

Free Fall -Constant Acceleration Example

Acceleration due to gravity: 9.8m/s2

This means that for every second an object
falls, its speed increases by 9.8m/s

Ignore air resistance

​https://youtu.be/E43-CfukEgs?feature=shared

Multiple Choice

A freefalling object...

• Has a constant velocity

• Has a constant acceleration

• Has no velocity

• Has no acceleration

Multiple Choice

An object that has been in freefall for 5 seconds has an acceleration of...

• 9.8 m/s2

• 14.8 m/s2

• 49 m/s2

• 98 m/s2