1. PHYSICS 11
TODAY:
Acceleration

2. Grading Scale for Physics11 (it might change) 2013/2014
Assignments (worksheets, labs, homework, pop-quizzes) 15% Quizzes (around 25 of them) 20% Unit Tests (7 of them – 5% each) 35% Projects (posters, ppt presentations, research etc..) 10% Final Exam 20%

3. Letter Grades for Physics11 (it might change) 2013/2014
A 100% – 86% B 85% – 73% C+ 72% – 67% C 66% – 60% D 59% - 50% F 49% - under

4. 2.2 ACCELERATION

5. WHAT HAPPENS TO ITS VELOCITY??
2.2 ACCELERATION
Imagine a train speeding up or slowing down…
WHAT HAPPENS TO ITS VELOCITY??
Whenever velocity changes:

6. 2.2 ACCELERATION

7. 3.2 ACCELERATION

8. ACCELERATION SI Units: meters per second square (m/s2)
It has DIRECTION and MAGNITUDE

9. from “rest” means (vi = 0 m/s) “comes to rest” means (vf = 0 m/s)
Find the acceleration of an amusement park ride that falls from rest to a speed of 28.0 m/s in 3.0 s
HINT:
from “rest” means (vi = 0 m/s)
“comes to rest” means (vf = 0 m/s)
9.3 m/s2

10. Speed Direction Velocity has two aspect to it:
Acceleration can occur under 3 conditions:

11. 3. Speed and Direction change
When…
1. Speed changes
2. Direction changes
3. Speed and Direction change

12. vf > v0 vf < v0 1. Speed changes The object is speeding up
slowing down
vf > v0
vf < v0

13. 1. Speed changes
The object is
speeding up

14. 1. Speed changes
The object is
slowing down

15. If direction changes, velocity changes because:

16. 3. Speed and Direction change

17. The car is slowing down…
Practice Problems: 2.2.1
(pg. 49)
m/s2
The car is slowing down…

18. Negative ACCELERATION Is an object speeding up OR slowing down?

19. Homework
Textbook: pg. 49 – PRACTICE B (1 – 5)

20. What can you say about displacement and velocity?
Magnitude and Direction of Acceleration
Imagine a train moving to the right…
What can you say about displacement and velocity?
STATION 1
STATION 2
displacement is positive
velocity is positive

21. velocity is not changing, therefore Δv is 0 m/s
Magnitude and Direction of Acceleration
Case #1:
Imagine a train going with no speeding up, or stopping = at a constant velocity
What can you say about velocity and acceleration?
STATION 1
STATION 2
velocity is not changing, therefore Δv is 0 m/s
acceleration is zero because velocity is constant

22. Magnitude and Direction of Acceleration
Case #2:
Imagine a train speeding up as it moves to the right …
STATION 1
STATION 2

23. What can you say about velocity?
Magnitude and Direction of Acceleration
Case #2:
Imagine a train speeding up as it moves to the right …
What can you say about velocity?
STATION 1
STATION 2
velocity’s magnitude increases (from 5 m/s to 10 m/s) so Δv will be positive

24. acceleration will be positive
Magnitude and Direction of Acceleration
Case #2:
Imagine a train speeding up as it moves to the right …
What can you say about acceleration?
STATION 1
STATION 2
acceleration will be positive
because the change in velocity (Δv) is positive

25. Magnitude and Direction of Acceleration
Case #3:
Imagine a train going in the positive direction, but it is slowing down (not stopping) as it approaches the next station
STATION 1
STATION 2
What can you say about displacement, velocity, change in velocity and acceleration?

26. displacement is positive because Δx (xf – xi) is > 0
Magnitude and Direction of Acceleration
Case #3:
Imagine a train going in the positive direction, but it is slowing down as it approaches the next station
STATION 1
STATION 2
displacement is positive
because Δx (xf – xi) is > 0

27. Magnitude and Direction of Acceleration velocity is still positive
Case #3:
Imagine a train going in the positive direction, but it is slowing down as it approaches the next station
STATION 1
STATION 2
velocity is still positive
(for example: vi = 10 m/s and vf = 2 m/s)
but Δv is negative
(vf – vi) is < 0

28. Magnitude and Direction of Acceleration acceleration is also negative
Case #3:
Imagine a train going in the positive direction, but it is slowing down as it approaches the next station
STATION 1
STATION 2
Because Δv is negative
acceleration is also negative

29. Magnitude and Direction of Acceleration
Case #4:
Imagine a train going in the negative direction, and it is speeding up as it approaches the next station
STATION -1
STATION 1
velocity is negative
(for example: vi = - 2 m/s and vf = - 10 m/s)
and Δv is negative
(vf – vi) is < 0

30. Because Δv is negative acceleration is also negative
Magnitude and Direction of Acceleration
Case #4:
Imagine a train going in the negative direction, and it is speeding up as it approaches the next station
STATION 1
STATION 2
Because Δv is negative
acceleration is also negative
Notice: acceleration is negative
and the object is speeding up!

31. Magnitude and Direction of Acceleration
Case #5:
Imagine a train going in the negative direction, and it is slowing down as it approaches the next station
STATION -1
STATION 1
velocity is negative
(for example: vi = - 10 m/s and vf = - 2 m/s)
and Δv is positive
(vf – vi) is > 0 (!!)

32. Because Δv is positive acceleration is also positive
Magnitude and Direction of Acceleration
Case #5:
Imagine a train going in the negative direction, and it is slowing down as it approaches the next station
STATION 1
STATION 2
Because Δv is positive
acceleration is also positive
Notice: acceleration is positive
and the object is slowing down!

33. SUMMARY
Speeding up
Slowing down

34. If Scott is moving in the NEGATIVE direction
Think About it…
When Scott is out for a bike ride, he slows down on his bike as he approaches a group of hikers on a trail.
Explain how his accelaration can be positive even though his speed is decreasing
If Scott is moving in the NEGATIVE direction
vi = -10 m/s
vf = -5 m/s
Slowing down
a = vf − vi Δt = (−5) − (−10) Δt = − Δt = 5 Δt = POSITIVE

35. Slope of velocity (speed) vs time graph = acceleration
The slope of the graph of velocity (speed) vs. time is the average acceleration
Slope of velocity (speed) vs time graph = acceleration
The equation for the line (y = mx +b) will have form: v = a·t + (y – intercept) v = 69t + 7.0

36. The slope at that point is positive = acceleration is POSITIVE
The slope of the graph of velocity (speed) vs. time is the average acceleration
Point A
The slope at that point is positive = acceleration is POSITIVE
The velocity in the positive direction is increasing (E.g. train just left the station and its speed is increasing)

37. The slope at that point is zero = acceleration is ZERO
The slope of the graph of velocity vs. time is the average acceleration
The slope at that point is zero = acceleration is ZERO
Point B
The velocity is constant (E.g. train is moving with out any change in velocity

38. The slope at that point is negative = acceleration is NEGATIVE
The slope of the graph of velocity vs. time is the average acceleration
Point C
The slope at that point is negative = acceleration is NEGATIVE
The velocity is decreasing over time (E.g. train is approaching a station, and it is slowing down

39. 2.2 Review Questions PAGE: 52 - 53 PROBLEMS: 1, 3, 5
HOMEWORK
2.2 Review Questions PAGE: PROBLEMS: 1, 3, 5

40. Acceleration vs. Time graph
Velocity vs. Time graph
Acceleration vs. Time graph
Area Under the Curve =
DISTANCE travelled
Area Under the Curve =
VELOCITY

41. Graphing Practice
Handouts

42. QUIZ
Thursday?