8.6B Speed, Velocity,
and Acceleration
On Level Notes
You will learn:
State Objective:
Differentiate between speed, velocity, and acceleration
I can:
If I give you real-life examples, can you tell me the difference
between speed, velocity, and acceleration
Read graphs with data about speed and acceleration
Speed: the distance an object
goes over a period of time
Different Types of Speed
• Average Speed
• Most common
• Will have a distance figure and a time figure
• Constant Speed
• Speed does not change
• On a speed graph, this looks like a rising, diagonal line
• On an acceleration graph, this looks like a flat plateau
Constant Speed in Graphs
The are both graphs for the same thing: constant speed
The graph on the left has distance over time (speed). The graph
on the right is speed over time (acceleration).
Always read the axes to make sure you know what its showing
you.
How to calculate average speed
from a graph?
1.
2.
3.
4.
Write your formula: s= d/t
Check your axes
Plug in your values
Calculate your answer
Practice Calculating Speed
1. What is on the Y axis? What is on the X axis?
2. To calculate speed, what 2 values do you need?
3. At one second, what was the average speed of this object in
m/s? Decimals are ok…just round to the nearest tenths place.
4. Is the object moving between 19 and 20 seconds? How do you
know?
Velocity: speed with direction
• Speed and velocity are almost the same
• Velocity is different because it includes the direction the
object is traveling
• If you are solving for velocity, you use the speed triangle
• Your answer should include a direction
Direction:
North
Up
South
Down
East
Left
West
Right
Can you find the velocity?
30 m/s South
20 miles per hour
.6 mm / year to the right
348 seconds
½ mile
30 miles to the west
4 inches/yr left
.97 m/s/s
85 km/min
29 cm/sec North
Velocity on a graph
Look at the graph from earlier. Notice how this is distance over
time, but they use the word “velocity”
Who uses velocity?
• Airplane pilots
• They need to know how fast AND which direction they need to go
• Meteorologists (Weather People)
• They study the speed and direction of storms…just like the ice
storm we just had!
• Military Positions
• They need to know at what angle to fire missiles, launch
satellites, direct unmanned drones.
Acceleration: 3 ways to
accelerate
Fancy Definition: rate of how the velocity changes
What it really means:
Acceleration is speeding up, slowing down, or changing
direction.
Yes, it is really 3 things and not just speeding up.
Acceleration: caused by forces
Acceleration is caused by unbalanced forces.
To speed up, we need to apply a force to increase the speed of
the object.
To slow down, we need to apply a force in the front of the
object to decrease the speed.
Even if the object’s speed doesn’t change, a force is require to
change its direction.
Acceleration on a Graph
The Y axis is velocity or speed
The X axis is time
Compare Speed and
Acceleration on a Graph
Really focus on your axes – which is it: speed or acceleration?
This shows an object speeding up over time.
Relationship: as the time increases, the acceleration increases
Comparing Speeds: moving or
not moving
These 2 graphs show balanced forces: the one on the left is moving
in a straight line in a constant speed. The one on the right is at rest
and will not move unless a force moves it.
Distance over time variety
This graph shows the movement of an object over a period of
time.
Comparing acceleration:
changing speed or same speed
Notice that this is speed over time: acceleration
Exit Ticket
1. What is the formula for Speed?
2. What is velocity?
3. What 3 ways can you accelerate?