physics; all the rest is stamp · 2014. 9. 8. · 5 *measuring & describing motion* 30 km 20 km...

“In science, there is only

physics; all the rest is stamp

collecting.” -Ernest Rutherford

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• Motion –occurs when something changes position

*Measuring & Describing motion* • Distance

–How far something has moved

Measured in: meters or kilometers

4 *Measuring & Describing motion*

Distance vs. Displacement

•Distance is how far an object has traveled

•Displacement is how far from the starting point an object actually moved

•Displacement does not equal distance traveled.

5 *Measuring & Describing motion*

30 km

20 km

15 km

15 km !

His Displacement is only 15 km.

6 *Measuring & Describing motion*

How fast Something Moves is SPEED

Speed is the distance an object travels in a certain period of

time.

7 *Measuring & Describing motion*

What is his rate of speed?

• Time= 30 min • What is his rate of speed? • Speed = distance/time • 1 km per min • 1 km/min

30 km

8 *Measuring & Describing motion*

Graphing Speed Constant Speed

9 *Measuring & Describing motion*

CONSTANT SPEED

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10 m/s

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S P E E D

What’s Happening Here? 12

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Velocity • In order to completely

describe the motion of an

object we need to include

not only the speed of the

object, but also

–the direction !

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If I told you that the moon man moved 40 km does that tell you where he is?

No.

You need to know the direction. 15

When describing velocity, you need to state the direction.

• Ex. 40 km/hr east

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Let’s Practice………… If a car travels

400m in 20

seconds , what

is its average

speed?

Practice ….#2

It takes Serina 0.25

hours to drive to

school. Her route is

16 km long. What is

Serina’s average

speed on her drive to

school?

…with a partner….

p.2..#s 1-8

Sometimes speed changes Changing Speed

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Acceleration • Changing Speed

–How fast the speed is changing. • Units: m/s2

–Velocity per sec –m/sec per sec

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• EX: If the acceleration is 10m/s2

•The object is increasing its speed by 10 m/s every sec.!

•How fast is it going after 5 sec.?

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•Acceleration: Changing Speed

•Covering more distance every second

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A cyclist

accelerates

from 0 m/s to

8 m/s in 3

seconds.

What is his

acceleration ?

Let’s Practice…………

A car advertisement

states that a certain

car can accelerate

from rest to 70 km/h

in 7 seconds. Find

the car’s average

acceleration.

10 m/s2

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Acceleration

•Can be positive or negative.

•Neg. Acc. Shows that the

object is slowing down.

•ACCELERATION IS IN THE

OPPOSITE DIRECTION FROM

THE VELOCITY!

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Cases of Acceleration 23

Changing Velocity

Constant Velocity

Which one’s which? 24

• During which of the following intervals are forces on the car balanced?

Hint: Balanced forces cause NO CHANGE in motion….

What is the child’s average speed for part A of her journey?

A

B

C

What’s Happening Here? 25

Instantaneous Speed 26

A. 7 km/hr B. 70 km/hr C. 300 km/hr D. 1750 km/hr

What is the average speed of a car that travels 350 kilometers in 5 hours?

EOCT QUESTIONS 27

1. Which graph(s) show(s) constant speed?

2. Which graph(s) show(s) acceleration?

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----- another

EOCT QUESTIONS

…with a partner….

p.2..#s 9-11 and

p.3..#s 12-16

THE END 29