Wednesday October 26, 2015
Thursday October 27, 2015
Unit Question
What role do forces play in the world around us?
Guiding Question What are the factors affecting acceleration?
/ Learning Target
Warm-up
Calculate the velocity of a bus that travels 80km East in 1.5
hours. Remember velocity = distance/time. Show your work!
80/1.5
= 53.3 km/h East
Agenda
1. Acceleration notes and practice
Homework
1. Quiz Friday!
Acceleration
• Acceleration – the rate at which velocity changes
• Can be an:
• Increase in speed
• Decrease in speed
• Change in direction
Types of acceleration
• Increasing speed
• Example: Car speeds up at green light
• Decreasing speed
• Example: Car slows down at stop light
• Changing Direction
• Example: Car takes turn (can be at constant speed)
screeeeech
Question
• How can a car be accelerating if its speed is a constant 65 km/h?
• If it is changing directions it is accelerating
Calculating Acceleration
• If an object is moving in a straight line
Final _ speed  Initial _ Speed
Acceleration 
Time

Units of acceleration:

m/s2
Acceleration is simply expressed as velocity per seconds. And Velocity as
meter per seconds. So the SI notation is m*s*s.
Calculating Acceleration
Initial
0s
0 m/s
Final _ Speed  Initial _ Speed
Acceleration 
Time
16m / s  0m / s

4s
 4m / s 2
Final
1s
4 m/s
2s
8 m/s
3s
12 m/s
4s
16 m/s
Graphing Acceleration
• Can use 2 kinds of graphs
• Speed vs. time
• Distance vs. time
Graphing Acceleration:
Speed vs. Time Graphs
14
Speed (m/s)
12
10
8
6
4
2
0
0
1
2
3
4
5
6
Time (s)
1)Speed is increasing with time = positive acceleration
2)Line is straight = acceleration is constant
Graphing Acceleration:
Speed vs. Time Graphs
14
Speed (m/s)
12
10
8
Rise = 4 m/s
6
4
Run = 2 s
2
0
0
1
2
3
4
5
6
Time (s)
3) In Speed vs. Time graphs:
Acceleration = Rise/Run
4) What is the acceleration of the object between
time 2 seconds and 4 seconds?
= 4 m/s ÷ 2 s = 2 m/s2
• You can use a graph to calculate acceleration.
• The slope of a speed-time graph is acceleration.
• The graphs below show 3 scenarios.
• Figure 1 shows a constant velocity and zero acceleration.
• Figure 2 shows a direct relationship with increasing velocity and positive
acceleration.
• Lastly Figure 3 shows a inverse relationship with decreasing velocity and negative
acceleration.
Positive
acceleration
Negative
acceleration
Graphing Acceleration:
Distance vs. Time Graphs
35
Distance (m)
30
25
20
15
10
5
0
0
1
2
3
4
5
Time (s)
1)On Distance vs. Time graphs a curved line means the
object is accelerating.
2)Curved line also means your speed is increasing.
Remember slope = speed.
Question:
35
Distance (m)
30
25
20
15
10
5
0
0
1
2
3
4
5
Time (s)a objects that are
The black and red lines represent
accelerating. Black is going a greater distance each second, so
it must be speeding up. Red is going less each second, so
1)Which
must
be slowingline
downrepresents an object that is
accelerating?
Remember: in distance vs. time graphs:
curved line = accelerating, flat line = constant speed
Question
14
Speed (m/s)
12
Run = 3 s
10
8
Rise = -6 m/s
6
4
2
0
0
1
2
3
4
5
6
Time (s)
Above is a graph showing the speed of a car over time.
1) How is the speed of the car changing (speeding up,
Slowing down, or staying the same)?
2) What is this car’s acceleration?
1) The car is slowing down
2)Acceleration = rise/run = -6m/s ÷3s = -2 m/s2
Question: Hard one
14
Speed (m/s)
12
10
8
6
4
2
0
0
1
2
3
4
5
6
Time (s)
Above is a graph showing the speed of a car over time.
1)What would a distance vs. time graph for this
look like?
Question: Hard one
14
Speed (m/s)
12
10
8
6
4
2
0
0
1
2
3
Time (s)
Is there acceleration?
YES!
What shape will the
distance/time graph
need to be?
Curved!
4
5
6
Question: Hard one
14
Speed (m/s)
12
10
8
6
4
2
0
0
What
is the speed doing?
What
is the distance doing?
What
1
2
Going down!
3
4
5
6
Time (s)
Going UP!
does that mean for the GAIN in
distance over time?
Distance over time goes up slowly!
Speed (m/s)
Distance (m)
Question: Hard one
14
45
12
40
35
10
30
258
206
15
4
10
52
00
0
0
1
1
2
2
3
3
Time (s)
(s)
Time
4
4
5
5
6
6
Distance over time goes up slowly in a curved line!
Exit Question
A car does not change its speed, but it is accelerating. How is this
possible? (use your acceleration notes)
• The car is changing direction! (A change in direction is
a change in velocity)