**Speed Video :**

The rate of change in distance with respect to time. Since speed is built from distance, a scalar quantity, then speed is also a scalar quantity. This means it carries no direction information with it.To know more about Speed ,watch Speed Video to learn more .

**Speed:**

Nearly everyone knows that the one moving faster (the one with the greater speed) will go farther than the one moving slower in the same amount of time. Either that or they’ll tell you that the one moving faster will get where it’s going before the slower one. Whatever speed is, it involves both distance and time. “Faster” means either “farther” (greater distance) or “sooner” (less time). Doubling one’s speed would mean doubling one’s distance traveled in a given amount of time. Doubling one’s speed would also mean halving the time required to travel a given distance. (The symbol *v* is used for speed because of the association between speed and velocity, which will be discussed shortly.)

- Speed is directly proportional to distance when time is constant:
*v*∝*s*(*t*constant) - Speed is inversely proportional to time when distance is constant:
*v*∝ ⅟*t*(*s*constant)

Combining these two rules together gives the definition of speed in symbolic form.

In order to calculate the speed of an object we must know how far it’s gone and how long it took to get there. “Farther” and “sooner” correspond to “faster”. Let’s say you drove a car from New York to Boston. The distance by road is roughly 300 km (200 miles). If the trip takes four hours, what was your speed? Applying the formula above gives

In order to emphasize this point, the equation is sometimes modified as follows

The line over the *v* indicates an average or a mean and the Δ (delta) symbols indicate a change.

Useful for CBSE, ICSE, NCERT & International Students

Grade : 9

Subject :Physics

Lesson : Motion

Topic: Speed Video

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