Speed and AccelerationMeasuring motion

Measuring Distance

Meter – international unit for measuring distance.

= 50 m1 mm

Calculating Speed

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

S = d/t

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

_

.__.

timeTotal

DistTotalSpeedAve

_

.__.

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

Who will win the race? LAB

Running the race LAB.

Question?

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

Demonstration

Two volunteers to race 10 meters there and back.

The racer with the fastest velocity wins.

Demonstration

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

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?

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.

Position vs. Time:

5 sec 10 sec 15 sec 20 sec 25 sec 30 sec

-6

-4

-2

0

2

4

6

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>