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# Speed and Velocity

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by

## Mr. Duke

on 25 February 2012

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#### Transcript of Speed and Velocity

A car traveling at 68 mph
(usually written m/h).
Speed is the
rate
at which something moves.

The
speed
of an object is the distance it travels over a certain amount of time.
Speed
The speed of the Milky Way galaxy is about 600 km/s.
Examples of speed:
How do you calculate speed?
Speed =
distancetime
For example, a cyclist travels 30 kilometers in 2 hours, and so her speed is 15 km/hr.
Speed =
30 km
2 hr
=
15 km/hr
How do you calculate speed?
Speed =
distance
time
Speed and
Velocity
Set world landspeed record in 1997: 763 mph.
Thrust SSC:
Instantaneous speed
is the rate at which an object is moving at a given instant in time.

Example: Car speedometer (60 mph right now)
How do you calculate speed?
Speed =
distance
time
Total distance (d) = 100 km + 50 km = 150 km

Total time (t) = 1 hr + .5 hr = 1.5 hr

Average speed (v) = =
100 km/hr
Speed
describes only how fast an object is moving
.

Velocity
gives both the speed
and
direction of the object's motion
.

60 km/hr
60 km/hr North
What's the difference?!?
150 km
1.5 hr
2 Types of Speed
1.
2.
average speed =
total time
total distance
Average Speed
is the total distance traveled (d) divided by the total time (t).
Example: You drive 100 kilometers over an hour, then pull over to eat. When finished eating, you drive another 50 kilometers which takes you half an hour.
http://video.nationalgeographic.com/video/the-magazine/the-magazine-latest/ngm-cheetah-speed-record/
Calculate the speed with which a sprinter runs, in meters per second, if she can cover 100 meters in 10 seconds.
Speed of sprinter = 100/10 = 10 m/s
A lion chasing a gazelle across the plains of Africa covers a distance of 400 feet in 30 seconds. If the gazelle is running at a speed of 13.5 ft/s will the lion be able to catch it?
Speed of lion = 400/30 = 13.3 ft/s
The gazelle is too fast!
Practice!
1 tire rotation = 3 ft
The time is takes for 1 rotation = .034 second
3/.034 = 88 ft/s
88 ft/s = 60 mph
Practice
time = distance / speed
distance = speed x time
How to calculate time and distance
What if the time for 1 rotation = 1 second?
3/1 = 3 ft/s
3 ft/s = 2 mph
You run 4 kilometers over an hour, then you stop for a break. You continue your run for another 6 kilometers which takes you an hour and a half. What was your average speed?
total distance = 4 km + 6 km =
10 km
total time = 1 hour +
1.5 hours
average speed =
10 km
/ 2
.5 hours
= 4
km/hr
How long does it take Cory to walk to school if he lives 2,000 meters away and his speed is 2 m/s?
time = 2,000 / 2 =
1,000 s
How far away from school does Joe live if it took him .5 hours to walk to school at 5 mi/h?
.5 x 5 =
2.5 miles
Speed or Velocity?
42.3 m/s

16 km/sec downhill

17 km/min South

12.5 km/hr
23.9 m/s

17.31 Northeast
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