Speed is the rate of change of distance . Velocity is the rate of change in displacement.

**Speed - Velocity**

** **

**Speed**

**Recapitulation**

In sixth standard we already studied
about the speed in detail.

1 km/h = 5/18 m/s

How we got this ?

1 km = 1000 m

1 h = 3600 s

1 km / h = 1000 m / 3600 s = 5/ 18 m /s

Speed is the rate of change of
distance .

Speed = distance /time

Unit is metre/second (m/s)

We can classify speed into two
types.

**Uniform speed**

If a body in motion covers equal
distances in equal intervals of time, then the body is said to be in uniform
speed.

**Non- uniform speed**

If a body covers unequal distances
in equal intervals of time, the body is said to be in non-uniform speed.

Average speed = total distance
travelled / time taken to travel the distance.

**Velocity**

Velocity is the rate of change in displacement.

Velocity (v) = displacement / time

SI unit of velocity is meter /
second (m/s).

If an athlete in the diagram takes
25 s to complete a 200 m sprint event. Find her speed and velocity.

Speed = distance / time

=200 / 25

=8 m/s

velocity = displacement /time

=50/25

=2 m/s

**Uniform velocity**

A body has uniform velocity, if it
covers equal displacement in the same direction in equal intervals of time. **E.g.**
light travels through vacuum.

**Non uniform velocity**

If either speed or direction
changes, the velocity is non uniform. **E.g.** a train starting and moving
out of the station.

**Average velocity**

Average velocity = total
displacement / total time taken

E.g. Figure shows a car that travels
5 km due east and makes a U â€“ turn to travel another 7 km. If the time taken
for the whole journey is 0.2 h. Calculate the average velocity of the car.

Average velocity = total
displacement/time taken. (taking the direction due east of point O as positive)

= (5â€“7)/0.2

= â€“2 / 0.2

= â€“10 km/h (or) â€“10 Ã— 5/18 =
25/9

= â€“0.28 m / s

The triangle method can help you to
recall the relationship between velocity (v), displacement (d), and time(t).

v = d / t , t = d / v, d = v Ã— t

**Answer
the following questions:**

***
Calculate the velocity of a car travelling with a uniform velocity covering 100
m distance in 4 seconds.**

Velocity = Sistance / time = 100/4 = 25 m/s

***
Usain Bolt covers 100 m distance in 9.58 seconds. Calculate his speed. Who will
be the winner if Usain Bolt comepetes with a Cheetah running at a speed of 30
m/s?**

Speed of Usain Bolt = 10.43 m/s

Speed of cheetah = 30 m/s

Cheetah will be the winner.

***
You are walking along east covering a distance of 4 m, then 2 m towards
south,then 4 m towards west and at last 2 m towards north. You cover the total
distancein 21 seconds, what is your average speed and average velocity?**

Total distance covered = 12 m

Total time taken =21 seconds

Average speed = Total distance covered / total time = 12m / 21 =
0.571 m/s

Average velocity = 0 m/s

12m / 21 = 0.571 m/s

Average velocity = 0 m/s

Average velocity is zero because the starting point and the
finishing point is same

âˆ´Displacement is zero so, average velocity is also

Average velocity = Total distance / time

Tags : Force and Motion | Term 1 Unit 2 | 7th Science , 7th Science : Term 1 Unit 2 : Force and Motion

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7th Science : Term 1 Unit 2 : Force and Motion : Speed - Velocity | Force and Motion | Term 1 Unit 2 | 7th Science

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