1. Speed, acceleration, momentum
Motion
Speed, acceleration, momentum

2. Frames of Reference Object or point from which motion is determined
Most common is the
earth
Motion is a change
in position relative to
a frame of reference

3. Speed Speed = Distance ÷ Time D_ S T
Example: A car travels 300km in 6 hours. What is the speed of the car?

4. Answer: Speed = distance ÷ time Speed = 300km ÷ 6 hours
Speed = 50km/hr

5. More practice
1. How far can a plane travel if it flies 800km/hr for 9 hours?
2. How long does it take a ship to go 500 km if it travels at a speed of 50km/hr?

6. Answer D
S T D
800km ▪ 9hrs = 7200km hr

7. Answer D
S T
500
50 T
500km ÷ 50km = 10 hrs hr

8. Velocity Speed in a given direction.
What is the velocity of a boat that travels from St. Peter to Mankato (10 miles) in 15 minutes?

9. Answer Speed = distance ÷ time Speed = 10 miles ÷ 15 minutes
Speed = 0.67 mi/min
Velocity = 0.67 mi/min South

10. Change your answer to mi/hr!
0.67mi/min x 60min/hr =
40 mi/hr

11. Distance-time graphs
On your paper, graph the following:
D (m) T (sec)
0 0
5 7

12. Distance (m)
time (sec)

13. Was your graph a straight line?
A distance-time graph which is a straight line indicates constant speed.
In constant speed, the object does not speed up or slow down. The acceleration is zero.

14. Graph the following on a distance-time graph:
D (m) T (s)
0 0
5 1
20 2
45 3
80 4

15. Distance (m)
time (sec)

16. Was your graph a curve?
A graph that curves on a distance-time graph shows that the object is accelerating

17. Distance-time graphs
Describe the motion of the object as shown in the graph.
From 0-8 sec,
constant speed: (25 m/sec)
From 8-12 sec,
no motion
From sec,
acceleration
From sec,
constant speed

18. Speed-time graphs
Using the distance-time graph from the last frame, draw a speed time graph. First fill in the table below:
Average Speed (m/s) Time (sec)
____ 0 to 8
____ 8 to 12
____ 12 to 20 25
37.5

19. What does your graph look like?
Constant speed will be a horizontal line on a speed time graph.
If the speed decreases, the line will slant down.
If the speed increases, the line will slant up.

20. What do the following speed-time graphs depict?

21. Acceleration Change in velocity Acceleration = ∆V/ ∆T ∆V
Can be change in speed or direction
Acceleration = ∆V/ ∆T ∆V
a t

22. Acceleration problem
A roller coaster’s velocity at the top of a hill is 10m/s. Two seconds later it reaches the bottom of the hill with a velocity of 26m/s. What is the acceleration of the roller coaster?

23. Answer Acceleration = ∆V/ ∆T a = 26m/s – 10m/s 2 s a = 16m/s 2s
a = 8m/s/s or 8m/s2

24. More acceleration problems
1. A car accelerates at a rate of 20mi/hr/s. How long does it take to reach a speed of 80 mi/hr?
2. A car travels at 60 miles per hour around a curve. Is the car accelerating?
3. A car travels in a straight line at 60mi/hr. Is the car accelerating?

25. Answers: 1. ∆V 80mi/hr a t 20mi/hr/s t 4sec = t
2. yes! Because it’s changing direction!
3. no! It’s not changing speed or direction!

26. Deceleration Negative acceleration
Example: A car slows from 60mi/hr to 20mi/hr in 4 seconds. What is its acceleration?

27. Answer: Acceleration = ∆V/ ∆T Acceleration = Vf – Vi t
a = 20mi/hr – 60mi/hr
4 s
a = -40mi/hr 4s
a = -10mi/hr/s

28. Review: Distance-time graph of acceleration

29. Distance-time graph of deceleration

30. Review:Speed-time graph of acceleration

31. Review: Speed-time graph of deceleration

32. Review: Distance-time graph of constant speed

33. Momentum Momentum = Mass x Velocity
Which has more momentum: a 300lb football player moving at 5m/s or a 200lb quarterback moving at 10m/s?

34. Answer: Momentum of the 300lb player is 300lbs x 5m/s = 1500lb-m/s
Momentum of the quarterback is
200lbs x 10m/s = 2000lb-m/s
The quarterback has a greater momentum!

35. Momentum problems
2 cars are heading east, car A is traveling 30mi/hr, car B is traveling 60mi/hr. Each car weighs 2000lbs.
What is the momentum of car A?
What is the momentum of car B?
If car B crashes into car A, what is the total momentum?

36. Answers: P=mv Car A’s momentum = 30mi/hr x 2000lbs
PA = 60,000 mi-lbs/hr east
Car B’s momentum = 60mi/hr x 2000lbs
PB = 120,000 mi-lbs/hr east
Total momentum = PA + PB
= 60, ,000
= 180,000 mi-lbs/hr east

37. Another momentum problem!
Car X is traveling 30mi/hr east, car Y is traveling 60mi/hr west. Each car weighs 2000lbs.
What is the momentum of car X?
What is the momentum of car Y?
If car X crashes into car Y, what is the total momentum?

38. Answers: P=mv Car X’s momentum = 30mi/hr x 2000lbs
PA = 60,000 mi-lbs/hr east
Car Y’s momentum = 60mi/hr x 2000lbs
PY = 120,000 mi-lbs/hr west
Total momentum = PY - PX
= 120, ,000
= 60,000 mi-lbs/hr west