Think about the motion probe and graphs that we made with our own bodies, and then answer the next few

questions…

Which of these graphs show constant speed toward

home?

Which of these graphs show constant speed away from

home?

Which of these graphs shows someone running away from home, resting a while, running away from home again, running toward

home, walking away from home, running away from home REALLY fast, and then running not quite as fast away from home?

Which of these graphs shows constant acceleration (speeding

up) toward home?

Which of these graphs shows constant acceleration (slowing

down) toward home?

Which of these graphs shows constant acceleration away from

home?

Which of these graphs shows an object at rest?

Which of these graphs shows an object moving at the fastest rate?

Which of these graphs shows an object moving at the slowest rate?

Which graph fits this story: Johnny ran away from his starting point, sat down to rest for a while, ran even faster to his friend’s house, and then raced

all the way back to the starting point?

Which graph fits this story: A dog was walking slowly along a street UNTIL he saw his master, at which point he turned and started running toward

home?

•Distance an object travels in one unit of time

•Speed

• 125 miles per hour• 125 m/hr• 125 mph• 20 cm/year• 20 centimeters per

year

•Examples of Speed

This car is in motion at a speed of 87 miles per hour.

Always includes distance

compared to

time

Speed

Example:This car can achieve a

speed of

125 miles per hour.

•Divide the distance that the object has traveled by the time that it took to travel the distance

•How to calculate speed:

DistanceSpeed = Time

Yes, speed =

dividedby

dividedby

•A cheetah chased an antelope across the field for 1 minute. During that time, he covered 5 kilometers. At what speed did he chase the antelope?

•Speed = Distance / Time = 5km / 1minute

= 5km / min

Let’s practice:

•It took an ant 4 minutes to walk 40 meters. At what speed did he walk?

•Speed = Distance / Time = 40 meters / 4 min

= 10 m / min

Let’s practice:

•It took a ball 60 seconds to roll 360 meters. At what speed did it roll?

•Speed = Distance / Time = 360 meters / 60 sec

= 6 meters per second

Let’s practice:

•Unchanging speed• Speed that remains the same• Speed that remains fast, not

changing• Speed that remains slow, not

changing

•Constant Speed

Go here to find the animation of three cars in a box. Can you tell which cars are accelerating and which car is moving at a constant speed?

•Which car is moving at a Constant Speed?

http://www.glenbrook.k12.il.us/gbssci/Phys/mmedia/kinema/acceln.html

The red car is moving at a constant speed.

•Judging from this graph, when did the car remain at rest?

Speed of a Car

0

5

10

15

20

25

30

35

Zero One Two Three Four Five Six Seven Eight

Time (in minutes)

Dis

tan

ce (

in m

iles

)

Can you see that the speed remained at 25 miles per minute from 5 – 7 minutes; so the car is not moving.

Average SpeedUsually objects do not move at a constant speed; instead, they keep changing their speeds.

Imagine yourself riding a bike ride to a friend’s house. You’d keep changing speeds as you rode to his/her house, wouldn’t you?

What if I asked the speed that you traveled to your friend’s house? You couldn’t answer just one speed; you’d have to answer many different speeds.

Well, I wouldn’t want to hear all of the speeds, I’d just want to know your average speed.

How would you calculate average speed? You’d do it like this…

Or you could write it this way…

Speed of a Car

0

5

10

15

20

25

30

35

Zero One Two Three Four Five Six Seven Eight

Time (in minutes)

Dis

tan

ce (

in m

iles)

In a graph, this would bethe total (or ending) time.

Quiz Yourself: Can you spot constant speed, acceleration, and average

speed?

Study the purple car closely. Can you tell that its speed keeps changing? It is true; this car’s speed is NOT constant. We won’t be able to find the constant speed of this car, but we will be able to find the AVERAGE SPEED of this car. We calculate average speed exactly the way the we calculate constant speed: by dividing the distance that the object traveled by the time it took to travel that distance.

Find the average speed of the purple car.

Go here to find the animation of a purple car moving along a 5-mile track that includes a stop light or two. http://www.glenbrook.k12.il.us/gbssci/Phys/mmedia/kinema/trip.html

•Check this graph again. Is the car moving at a constant speed? No. We can only find the average speed. Find

the avg. speed up to 5 min. What about 2 min?

Speed of a Car

0

5

10

15

20

25

30

35

Zero One Two Three Four Five Six Seven Eight

Time (in minutes)

Dis

tan

ce (

in m

iles)

Up to 5 min, speed = 5mph Up to 3 min, speed = 4 mph

In the following slides, you will use tables to discover data about speeds:

• The answers are at the bottom of each slide.

Try this sample test question:According to the tables below, which caris traveling at a constant speed?

Time(s)

Distance(m)

0 0

1 3

2 6

3 10

4 12

5 18

Time(s)

Distance(m)

0 0

1 4

2 8

3 12

4 16

5 20Idea from: http://www.physicsclassroom.com/mmedia/kinema/trip.html

Motion of Car A Motion of Car B

CarAB

Try this sample test question:According to the tables below, which caris traveling at a constant speed?

Time(s)

Distance(m)

0 0

1 3

2 6

3 9

4 12

5 15

Time(s)

Distance(m)

0 0

2 9

4 3

6 8

8 2

10 2Idea from: http://www.physicsclassroom.com/mmedia/kinema/trip.html

Motion of Car A Motion of Car B

Car B

Try this:According to the table below, what is the average speed of the car at 1 second? 2 seconds? 3 seconds? 5 seconds?

Time(s)

Distance(m)

0 0

1 4

2 8

3 15

4 20

5 35Idea from: http://www.physicsclassroom.com/mmedia/kinema/trip.html

Motion of Car A

Answers:

4 m/s

4 m/s

3 m/s

7 m/s

See Graphs that show data about speed…

According to the graph below, which biker traveled at an average speed of 5 m/sec?

Speeds of Bikers

0

5

10

15

20

25

30

35

Zero One Two Three Four Five

Time (seconds)

Dis

tan

ce (

met

ers)

Biker 1

Biker 2

Biker 3

Answer: Biker 1

According to the graph below, what is the average speed of Biker 3?

Speeds of Bikers

0

5

10

15

20

25

30

35

Zero One Two Three Four Five

Time (seconds)

Dis

tan

ce (

met

ers)

Biker 1

Biker 2

Biker 3

Answer: 6 meters/sec

How is the speed (distance/time) of an object

graphed?• We use a _ _ _ _ graph, since we

are showing how one o _ _ _ _ _’s distance is changing over _ _ _ _.

• On the x axis is the _ _ _ _ that the object was in motion.

• On the Y axis would be the _ _ _ _ _ _ _

_ that the object traveled during that time.

How is the speed (distance/time) of an object

graphed?• We use a line graph, since we are

showing how one object’s distance is changing over time.

• On the x axis is the time that the object was in motion.

• On the Y axis would be the distance that the object traveled during that time.

istance on Y

ime on X

According to the graph below, what is the average speed of Biker 2 up to three seconds?

Speeds of Bikers

0

5

10

15

20

25

30

35

Zero One Two Three Four Five

Time (seconds)

Dis

tan

ce (

met

ers)

Biker 1

Biker 2

Biker 3

Answer: 2 meters/sec