Motion

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# Motion - PowerPoint PPT Presentation

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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## PowerPoint Slideshow about 'Motion' - gari

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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 positionrelative to

a frame of reference

Speed
• Speed = Distance ÷ Time

D_

S T

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

• Speed = distance ÷ time
• Speed = 300km ÷ 6 hours
• Speed = 50km/hr
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?

1. D

S T

D

800 9

800km ▪ 9hrs = 7200km

hr

2. D

S T

500

50 T

500km ÷ 50km = 10 hrs

hr

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

0 0

5 7

10 14

15 21

Distance (m)

time (sec)

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:
• D (m) T (s)

0 0

5 1

20 2

45 3

80 4

125 5

Distance (m)

0 1 2 3 4 5

time (sec)

• A graph that curves on a distance-time graph shows that the object is accelerating
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
• 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?
• 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
• Change in velocity
• Can be change in speed or direction
• Acceleration = ∆V/ ∆T
• ∆V

a t

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?
• Acceleration = ∆V/ ∆T
• a = 26m/s – 10m/s

2 s

a = 16m/s

2s

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

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?

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

t

• a = 20mi/hr – 60mi/hr

4 s

a = -40mi/hr

4s

a = -10mi/hr/s

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?
• 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
• 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?
• 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!
• 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?
• 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