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**A cooling fan running at a fixed speed**

__Examples of uniform speed;__A car going along a straight level road at steady speed

An aircraft cruising at a level height and a steady speed

__Examples of non uniform speed;__falling stone, a ferris wheel, an elevator...

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__Characteristics of uniform motion :__===========================

1. Same distance is covered (traveled) in equal intervals of time.

2. Distance Time graph shows a straight line. s = v t

3. Speed is constant. If the body is moving in a straight line, velocity is constant and

acceleration is zero. There is no net force acting on the body. Displacement always

increases and is in one direction.

=================

__Non-Uniform motion__1. Body moves unequal distances in same time intervals.

2. Distance Time graph is not a straight line. Speed is not a constant.

3. If the body is moving along a straight line, velocity is in the same direction and

acceleration is also in the same direction. Velocity & acceleration are not constant.

===============

*Bodies moving in uniform speed*

__- Examples__1. Earth rotates around itself with a uniform speed (almost)

So all of us are moving with a uniform speed (tangential) in circles, with

respect to a stationary observer outside earth. We have not taken into

account the revolution of earth around Sun here.

Our speed = radius of earth * angular velocity

= 6400 km * 2 π / 24 hours = 1675.5 kmph

2. Trains and air planes move with uniform speed in between halts. Near

stations or airports, they accelerate or decelerate. An express train

covers usually around 60 km in 3/4 hour non-stop between two big stations.

average speed = 60 / (3/4) = 80 kmph

5. Speed of Birds flying in air = distance traveled / time = 15 meters /sec = 54 kmph

7. Hard disk inside the computer. It rotates at uniform speed.

speed = 4,000 rpm - 10,000 rpm

9. Light wave moves at uniform speed of c = 3 * 10^8 m/sec

10. A fan (ceiling) rotates at a uniform speed, same with the blade in a

kitchen - mixie or mixer.

Tip of Fan wing : radius = 0.80 meter,

smallest speed = 5 rotations per sec

Angular speed = 5 * 2 p radians/sec = 10 p rad/sec

Uniform Linear speed of the tip (far end of a wing)

= 0.80 * 10 p m/sec = 25.13m/s = 90.5 kmph

11. Blood inside our body moves (circulates) at uniform speed

Pulse rate = 72 /min

Average distance from heart to a hand/leg = 2.5 m

Speed of blood flow = around 2.5m * 72 / min

= 180 m / min = 180 * 60/1000 = 10.8 kmph

===============

__Bodies moving with non uniform speed :__1. In a cricket match the cricket ball is bowled and it travels the pitch at

an average speed in air and after bouncing from ground =

The ball takes 0.7 to 1 sec to reach batsman - observation.

speed = distance / time = 20 meters / 0.7 sec = 20/0.7 * 18/5 = 103 kmph for a pacer

and 20 m / 1 sec = 72 kmph for a spinner.

2. moon moves around the Earth with almost uniform speed

4. An object thrown in to air, like stone, moves at non-uniform speed.

4. Earth moves in an elliptical orbit non-uniform speed - its orbital speed

changes depending on its distance from the Sun. During summer Earth is

at 147 million km and (perihelon) during winter, it is at 152 million km.

Linear Speed at perihelon = 2 π R / T = 105,000 kmph

Linear Speed at apihelon = 2 π R / T = 109,000 kmph

5. Lift used to go up or down in a building - it moves at non-uniform speed -

accelerates and decelerates also. Lift reaches 4th floor (10meters) in

10 seconds with uniform acceleration starting from rest.

So acceleration of an elevator is = 20/100 = 0.2 m/s²

Speed = 0.2 * time m/sec