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Motion. Speed, acceleration, momentum. 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. Speed. Speed = Distance ÷ Time D_ S T

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motion

Motion

Speed, acceleration, momentum

frames of reference
Frames of Reference
  • Object or point from which motion is determined
  • Most common is the

earth

  • Motion is a change

in positionrelative to

a frame of reference

speed
Speed
  • Speed = Distance ÷ Time

D_

S T

Example: A car travels 300km in 6 hours. What is the speed of the car?

answer
Answer:
  • Speed = distance ÷ time
  • Speed = 300km ÷ 6 hours
  • Speed = 50km/hr
more practice
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?
answer1
Answer

1. D

S T

D

800 9

800km ▪ 9hrs = 7200km

hr

answer2
Answer

2. D

S T

500

50 T

500km ÷ 50km = 10 hrs

hr

velocity
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?
answer3
Answer
  • Speed = distance ÷ time
  • Speed = 10 miles ÷ 15 minutes
  • Speed = 0.67 mi/min
  • Velocity = 0.67 mi/min South
change your answer to mi hr
Change your answer to mi/hr!
  • 0.67mi/min x 60min/hr =
  • 40 mi/hr
distance time graphs
Distance-time graphs
  • On your paper, graph the following:
    • D (m) T (sec)

0 0

5 7

10 14

15 21

slide12

Distance (m)

time (sec)

was your graph a straight line
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.
graph the following on a distance time graph
Graph the following on a distance-time graph:
  • D (m) T (s)

0 0

5 1

20 2

45 3

80 4

125 5

slide15

Distance (m)

0 1 2 3 4 5

time (sec)

was your graph a curve
Was your graph a curve?
  • A graph that curves on a distance-time graph shows that the object is accelerating
distance time graphs1
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 12-16 sec,

acceleration

From 16-20 sec,

constant speed

speed time graphs
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

0

37.5

what does your graph look like
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.
acceleration
Acceleration
  • Change in velocity
    • Can be change in speed or direction
    • Acceleration = ∆V/ ∆T
    • ∆V

a t

acceleration problem
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?
answer4
Answer
  • Acceleration = ∆V/ ∆T
  • a = 26m/s – 10m/s

2 s

a = 16m/s

2s

a = 8m/s/s or 8m/s2

more acceleration problems
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?
answers
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!

deceleration
Deceleration
  • Negative acceleration
  • Example: A car slows from 60mi/hr to 20mi/hr in 4 seconds. What is its acceleration?
answer5
Answer:
  • Acceleration = ∆V/ ∆T
  • Acceleration = Vf – Vi

t

  • a = 20mi/hr – 60mi/hr

4 s

a = -40mi/hr

4s

a = -10mi/hr/s

momentum
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?
answer6
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!
momentum problems
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?
answers1
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 + 120,000

= 180,000 mi-lbs/hr east

another momentum problem
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?
answers2
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

= 60,000 mi-lbs/hr west