1. ACCELERATION
Science 10 – Physics Unit

2. Comparing Types of Motion
Uniform motion
Moves in a straight line with constant velocity
Speed and direction are constant
Feels smooth or like no motion is occurring
Non-uniform motion -- acceleration
Speed and/or direction is changing
Feels like being pushed or pulled

3. ACCELERATION Acceleration is a rate (over time) of change in velocity
Occurs whenever
Speed changes
Direction changes

4. ACCELERATION a = Δv a = ∆ v = v2 – v1 change in velocity a = Δv = m/s
Acceleration (a) is calculated as
a = ∆ v = v2 – v1 change in velocity
∆t = t2 – t change in time
Acceleration units are derived from velocity units (m/s) over time units (s)
Acceleration units are m/s/s = m/s2
a = Δv = m/s
Δt s

5. Equation Manipulation
a = Δv Δt
a Δt Δv a
Δt = tf – ti
Δt + ti
tf – Δt
Δv = vf – vi
Δv + vi
vf – Δv
tf =
vf =
Δv =
ti =
vi =
Δt =

6. Equation Manipulation
a = Δv Δt
Δv = a Δt
Δt = Δv a
a = vf – vi
tf – ti
vf – vi = a (tf – ti)
ti = tf = vf – vi a

7. Practice unit recognition
Measurement
25m
25s
25m/s
25m/s2
Property
Time
Velocity
Acceleration
Position

8. Acceleration BIG Acceleration means velocity is CHANGING QUICKLY
Means speed changes in short time interval
Means direction changes in short time interval
DOES NOT MEAN big velocity

9. Acceleration Small Acceleration means velocity is CHANGING SLOWLY
Means speed changes in long time interval
Means direction changes in long time interval
DOES NOT MEAN small velocity

10. Comparing Accelerations
Instantaneous acceleration – acceleration at a specific moment in time (*snaps)
Average acceleration – acceleration which occurs over a time interval
When acceleration is constant,
average equals instantaneous

11. Comparing Accelerations
Positive Acceleration means velocity is INCREASING
more speed over time
away from origin over time

12. Comparing Accelerations
Negative Acceleration means velocity is DECREASING
less speed over time
toward origin over time

13. Check Your Understanding:
Which measurement shows greatest acceleration?
(a) 25m/s 5s
(b) 25m/s 2s
(c) 25m/s
10s
(d) 25m/s
25s
Which measurement is an acceleration?
(a) 25s
(b) 25m/s
(c) 25m/s/s
(d) 25m
Smallest time interval
UNITS!

14. Constant “velocity” vs Constant “acceleration”
Comparing Constants
Constant “velocity” vs Constant “acceleration”
Constant velocity = no change in velocity
acceleration = ZERO
Constant acceleration = no change in rate of velocity
Velocity is changing at a constant rate

15. Visualizing Acceleration
metronome and marker (ticker timer)
Positive acceleration
• • • • •
more distance in same time, increasing velocity
Negative acceleration
• • • • •
Less distance in same time, decreasing velocity

16. Visualizing Acceleration
Velocity-Time Graphs – effect of time on velocity
Velocity labeled on y-axis
Time labeled on x-axis
Slope (line) represents acceleration
The steeper the slope, the greater acceleration – the greater the CHANGE IN velocity

17. Flat line represents ZERO acceleration – zero change in velocity --- constant velocity
Time
(s)
Velocity
(m/s) 10 1 2 3 4 5

18. Smooth sloping line upward represents increasing velocity
Time
(s)
Velocity
(m/s) 1 10 2 20 3 30 4 40 5 50

19. Smooth sloping line downward represents decreasing velocity
a = - 10m/s2 = slope
Time
(s)
Velocity
(m/s) 50 1 40 2 30 3 20 4 10 5
Velocity (m/s)
time (s)

20. Curved slope means changing acceleration

21. Practice Analysis 0-2s 4-7s 3s 5m/s
At which time interval is acceleration greatest?
At which time interval is acceleration zero?
How long does it take the object to slow to a stop?
What is the Δv of the blue line between 1s & 2s?
Practice Analysis
0-2s
4-7s 3s
5m/s

22. Practice Analysis Blue (A) Purple (C) Blue (A) (E)
Which line shows negative acceleration?
Which line shows zero acceleration?
Which line shows greatest constant acceleration?
Which line shows changing acceleration?
Practice Analysis E
Blue (A)
Purple (C)
Blue (A)
(E)

23. Calculating acceleration
Suppose a car going in a straight line is moving at 35km/hr at 3 seconds and 50km/h at 8 seconds. What is the acceleration of the car?
a = vf – vi
tf – ti
Given
Unknown
Equation
Solution
Sentence

24. Calculating acceleration
What is the acceleration of a vehicle that changes its velocity from 100 km/h to a dead stop in 10s?
a = vf – vi Δt G U E S

25. Calculating time interval
When the shuttle bus comes to a sudden stop to avoid hitting a dog, it accelerates uniformly at 4.1m/s2 as it slows from 9.0m/s to 0m/s. Find the time interval of acceleration for the bus.
a = vf – vi Δt
vf – vi = aΔt
Δt = vf – vi a G U E S