1. Day 2 At A Glance So today will have the following: 1) HW Talk
2) Acceleration talk
3) Together we explore the effect of acceleration and + and – signs upon motion.

2. QUESTIONS ABOUT THE HW?
Did you correctly do the HW? Questions?

3. LETS GET IT STARTED! Get clickers right now please.
Remember, this is to be done INVIDIDUALLY and HONESTLY.
Do NOT discuss with partners.

4. This person throws a ball up. The ball starts 1.5m off the ground.
The ball goes up 1 m then falls back down.
Which of the following is the correct MAGNITUDE of the displacement?
A) 1m
B) 1.5m
C) 2.5m
D) 4m

5. Displacement is change in position.
Magnitude means AMOUNT
Ball started at 1m above, ended at ground (0m above).
Δx = x final – x initial.
= (0 – 1) = -1m
But the – is a direction, so MAGNITUDE just means the value. 1m

6. This person throws a ball up. The ball starts 1.5m off the ground.
The ball goes up 1 m then falls back down.
Which of the following is the correct DIRECTION of the displacement?
A) Down
B) Up

7. Displacement is change in position.
Direction is the sign from earlier.
Negative, which in this case means DOWN.
After all, the ball ENDED below where it started.

8. This person throws a ball up. The ball starts 1.5m off the ground.
The ball goes up 1 m then falls back down.
If the person would throw the ball up at a FASTER velocity, would the average displacement for the entire throw
A) Increase
B) Decrease
C) Not Change

9. Displacement is change in position.
Throwing it up harder makes it travel further up in the air.
HOWEVER, the AVERAGE displacement for the ENTIRE THROW still relies on the start and end points.
Since they don’t change, neither does the average displacement. NO CHANGE.
It DOES change the displacement from the start to the max height and others, but that was not asked.

10. How would you describe how the velocity changed during the balls motion in the air? (Up is +)
A) The velocity started at zero, increased until it reached the top, then decreased as it fell.
B) The velocity started at a + value, increased until it reached the top, then decreased as it fell
C) The velocity started at a + value, decreased until it reached the top, then increased as it fell.
D) The velocity started at zero, increased until it reached the top, then increased as it fell

11. Notice the wording… in the AIR.
So if the ball is in the air, it is already moving UP since otherwise it would simply drop to the ground.
So the ball has a starting + initial velocity.
As it is going UP, it slows (due to…. ), but is still +.
At the top, it transitions from + (up) to – (down). Which means it hits a velocity of 0.
Then it gets faster going down (due to… ) until it hits. C

12. SO WHAT WAS IMPORTANT
The conditions of the problem situation give you an idea of how to think.
Determine the start and end point of what is being investigated.
Direction and sign need to be evaluated.

13. Lets Hear From The British
Lets see how to think of displacement and distance.

14. How does the overall displacement compare between the two?
They are the same due to same start and end point. Time does not matter. So both are ZERO.
How does the net velocity for each compare?
They are both zero for the net/overall race (As defined as d of race being from start point to end point).
How does the velocity after ten seconds compare for each?
Different! The plane has more velocity since it is further from the start after 10 seconds than the car.
Is there any point or time in this race where the car’s velocity is > the airplane’s velocity?
Yes! The first few moments of the race. The CAR was able to get to its max VELOCITY before the PLANE could. That idea is called……

15. MY TIME Acceleration: The change of velocity in a period of time.
Magnitude and Direction are key.
Quick thinking tip: Acceleration as velocity per second.

16. UNITS OF MEASUREMENT
Displacement:
Velocity:
Acceleration:
Time:

17. So lets have a car with an acceleration of +1m/s2 starting at rest.
Put in words the MOTION

18. So lets have a car with an acceleration of +1m/s2 starting at +5m/s.
Put in words the MOTION

19. So lets have a car with an acceleration of +1m/s2 starting at -5m/s.
Put in words the MOTION

20. Lets now talk Acceleration and Direction.
How I want you to try this:
Displacement is +/- and getting larger/smaller
Velocity is…
Acceleration is…
Leave room to do 2 graphs (no numbers)

21. 1) Car going forward, hits the gas

22. 2) Car going forward, hits the brakes

23. 3) Car going forward, put into reverse

24. 4) Car going backward, hits the gas

25. 5) Car going backward, hits the brakes

26. Now lets go back and graph the VELOCITY as time goes on for each!

27. Now lets go back and graph the POSITION as time goes on for each!

28. Acceleration Quick review: The change of velocity in a time period.
For ‘Free-fall’, where ‘gravity’ is the only thing acting on an object, we can say: a = for labs a = for ex

29. 1st Scenario For Review
A Car starts at +12m/s and brakes for 2 seconds until it is going +2m/s. What is the acceleration?
What are the correct signs for displacement, average velocity and acceleration here?

30. 1st Scenario For Review
A Car starts at +12m/s and brakes for 2 seconds until it is going -2m/s. What is the acceleration?
What are the correct signs for displacement, average velocity and acceleration here?

31. 2nd Scenario For Review - VOTE
A person is on a track starting at rest and accelerates to a fast + velocity. Which is the correct position vs. time graph?

32. Lets determine the information for each segment
x= 20m
x= 5m
x= 15m
x= m
Time
0 Sec
1 Sec
2 Sec
3 Sec
4 Sec
Position
Displ.
Velocity

33. If we were to find the VELOCITY in each segment, where would it be occurring?
x= 20m
x= 5m
x= 15m
x= m

34. Watch this progression of motion (each time period is 1 second)
Watch this progression of motion (each time period is 1 second). Assume it started AT REST.
Since the position is increasing by a larger amount every second, it is ACCELERATING t1 t4 t2 t3
x= 3.75m
x= 22.5m
x= .75m
x= 10.5m
Time
0 Sec
1 Sec
2 Sec
3 Sec
4 Sec
Position
.75
3.75
10.5
22.5
Displ. 3
6.75 12

35. If we were to find the VELOCITY in each segment, where would it be occuring?
x= 3.75m
x= 22.5m
x= .75m
x= 10.5m