Speed & Velocity

Speed & Velocity

Speed – is the ratio of the distance an object moves to the amount of time the object moves

How far an object moves over a period of time!!!

SPEED

How far an object moves over a period of time!!!SPEED

v = d / t

How far an object moves over a period of time!!!SPEED

v = d / tIf the girl ran a distance of 30 meters in

10 seconds , how fast did she run?

SPEED3 types of speed

Average speed – total distance divided by total time of travel

* Could be used during a race to describe the speed of a boat over the entire race, not just at one moment during the race.

SPEED3 types of speed

Instantaneous speed – the speed at any given instant

An example would be when you look at the speedometer on your car. It is telling you how fast you are traveling at that instant.

Do not attempt to travel at this speed!

SPEED3 types of speed

Constant speed – a speed that does not change

An example would be when you use the cruise control feature on your car. Your speed doesn’t change as you travel.

http://auto.howstuffworks.com/cruise-control1.htm

Velocity - is a description of both speed the object is traveling and the direction of motion of that object.

Velocity

Speed + Direction

For example if I said the wind is traveling at 10 miles/hour from the NorthI would be telling you the VELOCITY of the wind, not just the speed of it.

When is speed better than velocity?

Velocity

Would a sprint car fanatic care about the Speed of the car as it goes around thetrack?

Would a sprint car fanatic care about the direction of the car as it goes around thetrack?

Yes

No

When is velocity better than speed?

Velocity

If you were listening to the radio and the DJ said their was atornado warning issued. “A tornado was just spotted in North Fargo traveling at 40 miles / hour” would you be satisfied with just the speed of the tornado??

You would want to know the velocity of the tornado, if you knewIt was headed away from you, you could relax a little. If it washeaded towards you, you could take cover. So the radio announcer should say “A tornado was just spotted in North Fargo traveling North at 40 miles / hour.

NO!!

Graphing Speed

We can use a speed graph (showing distance over time) to describe the motion of an object. Let’s use this graph to describe the motion of a car at three different time periods.

Graphing Speed

Period 1 – from 0-3 seconds – What is the car doing?

The car has moved from 15 meters in just 3 seconds – we can just simply say that the car is MOVING (moving at a constant speed because the line is straight)

Graphing Speed

Period 2 – from 3-5 seconds – What is the car doing?

The car has not changed it’s distance– we can just simply say that the car is NOT MOVING (it’s speed is still constant)

Graphing Speed

Period 3 – from 5-9 seconds – What is the car doing?

The car has moved from 10 meters in 4 seconds – we can just simply say that the car is MOVING again. (moving at a constant speed because the line is straight)

Graphing Speed

Comparing Period 1 & Period 3 – What is the car doing?

In both cases the car is MOVING, but are they moving the same?

No! When the slope of the line is greater – the car travels further in a shorter time, therefore the car is moving faster – It is moving faster in the first 3 seconds of travel.