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Units for speed
Depends, but will always be a distance unit / a time unit
Ex. Cars: mi./h Jets: km/h Snails: cm/s Falling objects: m/s
Calculating speed
If I travel 100 kilometer in one hour then I have a speed of…
100 km/h
If I travel 1 meter in 1 second then I have a speed of….
1 m/s
S = d/t
Average speed
Speed is usually NOT CONSTANT Ex. Cars stop and go regularly Runners go slower uphill than downhill
Average speed = total distance traveled/total time taken.
Calculating Average Speed
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: 40 km + 20 km = 60 km
Total Time: 1 h + 2 h = 3 hr
Ave. Speed: total d/total t = 60 km/3 h = 20 km/h
timeTotal
DistTotalSpeedAve
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timeTotal
DistTotalSpeedAve
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Question
I travelled 25 km in 10 minutes. How many meters have I travelled? A) 25000 m 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 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? A) 100 m/min 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 B) 2000 m/min C) 10 m/min D) 200 m/min E) 20 m/min
Total Dist. = 1000 m + 1000 m = 2000 m
Total Time = 3 min + 7 min = 10 min
Ave speed = total dist/total time =
2000m/10 min = 200 m/min = D
Demonstration
Two volunteers to race 10 meters there and back.
The racer with the fastest velocity wins.
Velocity
Velocity – the SPEED and DIRECTION of an object.
Example: An airplane moving North at 500 mph A missile moving towards you at 200 m/s
Question
What is the difference between speed and velocity?
Speed is just distance/time. Velocity includes direction as well.
Velocity Vectors The direction and magnitude (amount) of
speed is represented by arrows. The length represents the magnitude,
and the arrow points in the direction of the speed
A slow speed A faster speed
In any direction the object moves
Position vs. Time Graphs
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.
Velocity vs. Time
You can also represent velocity instead of position.
We’ll be using a simulation to help visualize and practice creating and inferring an object’s motion
Velocity vs. Time
5 sec 10 sec 15 sec 20 sec 25 sec 30 sec
-4
-2
0
2
4
6
8
You can also determine an objects speed. What does this graph tell you about the person’s speed?
METERS
TIME
Phet Sim: Moving Man
Purpose: To be able to create and read graphs to describe the motion of an object.
<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; font-family: Arial,sans-serif;">Click to Run</td></tr></table></a></div>