Measuring motion

Measuring Distance
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Meter – international unit for measuring distance.
1 mm = 50 m

Calculating Speed
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Speed (S) = distance traveled (d) / the amount of time taken (t).
S = d/t

Units for speed
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Depends, but will always be a distance unit / a time unit
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Ex. Cars: mi./h
Jets: km/h
Snails: cm/s
Falling objects: m/s

Calculating speed
S = d/t
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If I travel 100 kilometer in one hour then I have a speed of…
100 km/h
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If I travel 1 meter in 1 second then
I have a speed of….
1 m/s

Average speed
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Speed is usually NOT CONSTANT
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Ex. Cars stop and go regularly
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Runners go slower uphill than downhill
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Average speed = total distance traveled/total time taken.

Calculating Average Speed
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I took 1 hour to go 40 km on the highway. Then it took me 2 more hours to go 20 km using the streets.
Total Distance:
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40 km + 20 km = 60 km
Total Time:
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1 h + 2 h = 3 hr
Ave. Speed:
 total d/total t = 60 km/3 h = 20 km/h
Ave .
_ Speed

Total _ Dist .
Total _ time

Question

I travelled 25 km in 10 minutes.
How many meters have I travelled?
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A) 25000 m
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B) .0112 m
C) .025 m
D) 2.5 m
Answer on next slide.

Question

I travelled 25 km in 10 minutes.
How many meters have I travelled?

A) 25000 m
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
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B) .0112 m
C) .025 m
D) 2.5 m
25 km * 1000m/km = 25000 m

Question

I ran 1000 m in 3 minutes. Then ran another 1000 m uphill in 7 minutes. What is my average speed?
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A) 100 m/min
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B) 2000 m/min
C) 10 m/min
D) 200 m/min
E) 20 m/min
Answer on next slide

Question

I ran 1000 m in 3 minutes. Then ran another 1000 m uphill in 7 minutes. What is my average speed?
A) 100 m/min 2000 m
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B) 2000 m/min
C) 10 m/min 10 min
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D) 200 m/min
E) 20 m/min
2000m/10 min = 200 m/min = D

Who will win the race? LAB
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Running the race LAB.

Question?
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What do you think of when you hear the word “velocity”.

Demonstration
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Two volunteers to race 10 meters there and back.
The racer with the fastest velocity wins.

Demonstration
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Ha! No one wins, because the race ended in the same position as the start position.

Velocity
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Velocity – the SPEED and
DIRECTION of an object.
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Example:
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An airplane moving North at 500 mph
A missile moving towards you at 200 m/s

Question
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What is the difference between speed and velocity?

Question
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What is the difference between speed and velocity?
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Speed is just distance/time. Velocity includes direction as well.

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Velocity Vectors
The direction and magnitude (amount) of speed is represented by arrows.
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The length represents the magnitude, and the arrow points in the direction of the speed
A slow speed A faster speed
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In any direction the object moves

Position vs. Time Graphs
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You can show the motion of an object using a graph or
Infer the motion of an object from a graph.

Position vs. Time Graphs:
What would it look like?
For example:
 walk from the hallway through the door to the back of the room,
 stop and look at the DMA on the board,
 then go back to pick up the hand out you forgot, then back to your seat at the back of the classroom.

Position vs. Time:
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5 sec 10 sec 15 sec 20 sec 25 sec 30 sec

Velocity vs. Time
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You can also represent velocity instead of position.
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We’ll be using a simulation to help visualize and practice creating and inferring an object’s motion

R
S
T
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M
E
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Velocity vs. Time
You can also determine an objects speed. What does this graph tell you about the person’s speed?
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5 sec 10 sec 15 sec 20 sec 25 sec 30 sec
TIME

Phet Sim: Moving Man
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Purpose: To be able to create and read graphs to describe the motion of an object.
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<div style="position: relative; width: 300px; height: 226px;"><a href="http://phet.colorado.edu/sims/moving-man/moving-man_en.jnlp" style="text-decoration: none;"><img src="http://phet.colorado.edu/sims/moving-man/moving-man-screenshot.png" alt="The Moving Man" style="border: none;" width="300" height="226"/><div style="position: absolute; width: 200px; height: 80px; left: 50px; top: 73px; background-color: #FFF; opacity: 0.6; filter: alpha(opacity = 60);"></div><table style="position: absolute; width: 200px; height: 80px; left: 50px; top: 73px;"><tr><td style="text-align: center; color: #000; font-size: 24px; fontfamily: Arial,sans-serif;">Click to Run</td></tr></table></a></div>