Chapter 10: Motion

The BIG idea: The motion of an object can be described and predicted

Key Concepts:10.1: An object in motion changes position10.2: Speed measures how fast position changes10.3: Acceleration measures how fast velocity changes

Warm-up• Suppose you pass a table on which a ball is sitting near the

end of a cardboard tube. After a few minutes, you pass the table again. The ball is now near the other end of the tube. What can you say about the motion of the ball between those two times? What can’t you say about the motion?

• You can say that the ball moved from one end of the tube to another.

• You can’t say anything about the path. The ball may have gone through the tube, or it may have been moved around the tube.

• Would you know speed? Velocity?• If you know time, but don’t know distance, you can’t know

speed or velocity!

Key Concepts (10.2)

•How is speed related to distance and time?•Speed is distance divided by time.•How would decreasing the time it takes

you to run a certain distance affect your speed?

•Your speed would increase.•What two things do you need to know to

describe the velocity of an object?•Speed and direction of motion

Chapter 10: Motion

•10.1 An object in motion changes position•10.2 Speed measures how fast position

changes•10.3 Acceleration measures how fast

velocity changes

10.2 Speed measures how fast position changes•Position can change at different rates

▫How far is it? Several blocks vs 5-minute walk The 5-min walk bases your time estimate on the distance to

the place and the person’s speed V = D/t D = V x t t = D/V

▫Speed – measure of how fast something moves or the distance it moves, in a given amount of time Greater the speed the faster an object changes position

▫Rate – the way in which one quantity changes compared to another quantity (“_____ per ______”) Speed: rate at which distance changes compared to time Pay rate: amount you are compensated compared to time

(per hour) Heart rate: measure of the number of heartbeats per

minute Fuel efficiency: measure of miles per gallon

Calculating Speed• Speed (V or S): Need to know both distance and time –

distance traveled over a certain time

• If you know the speed and time, you can figure out distance (D)

• If you know the speed and distance, you can figure out time (t)

• V = D/t D = V * t t = D/V• S = D/t D = S * t t = D/S

• Bikers traveling 4 m/s, and 2 m/s ▫ How far do each go in 5 seconds?

• Meters per second: m/s – standard unit for speed▫ Also km/hr and mi/h or mph

• 100-meter course in 20 seconds, speed in m/s?• 200m in 25 s. Speed?• 100m in 50 s. Speed?

Average Speed•Speed is not constant, though at each moment

you have a specific speed: “instantaneous speed” – difficult to measure

•Average speed: easier to calculate, over a distance▫Speed per lap of a track or pool during a race▫1600m race, 83s, 81s, 79s, 77s laps (400m each)▫Speed for lap one: 400m/83s = ▫Lap two: 400m/81s =▫Lap three: 400m/79s =▫Lap four: 400m/77s =▫Total time: 320 s, total distance: 1600 m; average

speed =

Distance-Time Graphs• Shows how speed relates to distance and time• Time is on the horizontal (x-axis), distance on the

vertical (y-axis)• How fast during first 6 seconds: S = D/t• During last 4 s?• Average speed over full 10 s?

Time (s)

Velocity includes speed and direction

• Velocity: speed in a specific direction▫ “walking east at a speed of 3 m/s”▫ Different velocity than “walking north at a speed of 3 m/s”…

but same speed▫ A change in either speed or direction results in a change in

velocity▫ Velocity is a vector quantity:

Vector: a quantity that has both size and direction

• Average speed depends on total distance traveled…average velocity depends on the total distance you are from where you started

• Travel north 400 miles at 30km/hr, then south 400 miles at 30km/hr

• Average speed of the trip is 30 km/hr • Average velocity of the trip is??• 0 km/hr because you ended up exactly where you started!

Math in Science – Working with Units: Time, Distance, and Speed•A cheetah runs at a speed of 30 meters

per second. How long does the cheetah take to run 90 meters?

Math in Science – Working with Units: Time, Distance, and Speed•How long would it take an object raveling

12 m/s to go 60 m?

Math in Science – Working with Units: Time, Distance, and Speed•If a car travels 60 km/h, how long would it

take the car to travel 300 km?

Math in Science – Working with Units: Time, Distance, and Speed•If a man walks 3 miles in 1 hour, what is

his speed? (in m/s?)

Critical Thinking (10.2)

•Amy and Ellie left school at the same time. Amy lives farther away than Ellie, but she and Ellie arrived at their homes at the same time. Compare the girls’ speeds.

•Amy traveled faster than Ellie.•Carlos lives 100 m away from his friend’s

home. What is his average speed if he reaches his friend’s home in 50 s?

•S = d/t = 100m / 50s = 2 m/s

How does the shape of the car affect the way it moves? Design your own car, and see how fast it can go!