Linear Motion

Linear Motion Let’s get down and derty 7/10/04

Linear Motion - Mr. Blount

1

Carl Lewis has run 100 m in 9.92 s. At this speed Carl covers 10.1 m per second. But because he starts from rest and accelerates up to speed, his top speed is more than this – about 10% over his average speed.

7/10/04

Linear Motion - Mr. Blount

2

Downhill skiers attain speeds of 70 to 80 mph on winding runs inclined about 10-15 degrees. A speed of 70 mph is 102.7 ft/s, which means a skier covers 10.3 ft in 0.1 s.

7/10/04

Linear Motion - Mr. Blount

3

Michael Jordan’s hang time at the peak of his basketball career was less than 0.9 s. Height jumped is less than 4 feet.

7/10/04

Linear Motion - Mr. Blount

4

Baseball pitchers such as Roger Clemens and Nolan Ryan can throw a baseball nearly 100 mph. Since the pitcher’s mound is 60.5 ft from home plate, the ball takes less than ½ second to get to the batter. Due to the pitcher’s reach, actual distance is about 55 ft. Because of air drag, a 95 mph ball slows to about 87 mpg, giving a travel time of 0.41 s. On average it takes 0.2 s for a batter to get his bat from its cocked position up to speed in the hitting zone, so he must react to the pitcher’s motion in a quarter-second or less, beginning his swing when the ball is only a little more than half the distance to the plate. 7/10/04

Linear Motion - Mr. Blount

5

What means of motion has done more to shape the way cities are built than any other? The Elevator.

7/10/04

Linear Motion - Mr. Blount

6

A special relationship. “Dert” Distance = rate x time This only applies when there is not acceleration

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Linear Motion - Mr. Blount

7

If you ride a bike a distance of 5m in 1s, what is your speed? For 10 m in 2 s? For 100 m in 20 s?

7/10/04

Linear Motion - Mr. Blount

8

How does instantaneous speed compare to average speed? Average speed is obtained from calculating the speed with dert over a time interval. Instantaneous speed is the speed at that instant. For example on an speedometer.

7/10/04

Linear Motion - Mr. Blount

9

Distance vs. Displacement  Race Track measurements  Distance = A measurement of the space

covered during a time interval.  Displacement = a measurement of the space between the starting point and the finishing point after a particle has moved during a time interval.

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Linear Motion - Mr. Blount

10

Velocity   

Blind man’s bluff Speed Direction For example; 12 mph North

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Linear Motion - Mr. Blount

11

If an airplane travels 500 km due north in 1 hr, what is its velocity? 250 km due north in ½ hr? 125 km north in ¼ hr?

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Linear Motion - Mr. Blount

12

Acceleration

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Linear Motion - Mr. Blount

13

Motion with Acceleration  v = at

velocity with acceleration  d = ½ at2

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Linear Motion - Mr. Blount

14

Reflect  Think of the relationships between

position, velocity and acceleration you explored in the Walking Lab.

7/10/04

Linear Motion - Mr. Blount

15

What is the acceleration of a car that goes from 0 to 100 km/hr in 10 s? What is the acceleration of a mechanical part that moves from 0 to 10 m/s in a time of 1s?

7/10/04

Linear Motion - Mr. Blount

16

Find the number of kilometers in a light year. Light travels 300,000 km/s. 300,000 km x 3600 s x 24 hr x 365 day = 1s 1 hr 1 day 1 yr 9460800000000 km

7/10/04

Linear Motion - Mr. Blount

17

Why is it an object can accelerate at a constant speed but not at a constant velocity? During constant speed the direction can be changing which causes an acceleration. During constant velocity neither the direction or speed change. So the acceleration is zero.

7/10/04

Linear Motion - Mr. Blount

18

Which has more acceleration when moving in a straight line – a car increasing its speed from 50 to 60 km/hr, or a bicycle that goes from 0 to 10 km/hr in the same time? They both have the same acceleration. The same change in velocity during the same time interval.

7/10/04

Linear Motion - Mr. Blount

19

Air Resistance Do objects fall at the same rate?

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Linear Motion - Mr. Blount

20

Acceleration due to gravity 10 m/s/s

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Second

Instantaneous Speed

0

0

1

10

2

20

3

30

4

40 Linear Motion - Mr. Blount

21

Displacement fallen in free fall. d = ½ gt2 or d = 5t2

7/10/04

Linear Motion - Mr. Blount

22

How far will a freely falling object that is released from rest, fall in 2 seconds? In 10 seconds? In ½ second?

7/10/04

Linear Motion - Mr. Blount

23

It’s all relative All motion is relative to a fixed reference point. Sometimes this reference is called a frame of reference.

7/10/04

Linear Motion - Mr. Blount

24

Consider a rifle fired straight downward from a high altitude balloon. If the muzzle velocity is 100 m/s and air resistance can be neglected, what is the acceleration of the bullet after one second? 7/10/04

Linear Motion - Mr. Blount

25

Consider a rifle fired straight downward from a high altitude balloon. If the muzzle velocity is 100 m/s and air resistance can be neglected, what is the velocity of the bullet after one second? 7/10/04

Linear Motion - Mr. Blount

26

Summary        

d = vt v = at or v = gt for free fall d = ½ gt2 for free fall. Distance Displacement Speed is the rate that position changes. Velocity is speed with direction. Acceleration is the rate at which velocity changes.

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Linear Motion - Mr. Blount

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