Question

Examples of uniform and non uniform speed

Answer 1

Uniform motion:
- When a cyclist is covering 5km uniformly in every 1 hour
- a vehicle moving at constant speed on a straight road

Non-uniform motion:
- motion of a football player
- motion of a bike in a busy road

Answer 2

  Characteristics of uniform motion :
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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.

4. If body is moving in a circle, the speed v is constant and acceleration = v²/R . Acceleration 
    points towards the center of circle. There is a centripetal force acting on the body. 
     Displacement increases and decreases in magnitude and changes in direction.
    Centripetal force is constant.

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.
4. If the body is moving in a circle, then speed, velocity, acceleration are not constant.
5. Angular velocity is not constant. Centripetal force is not constant.

Bodies moving in uniform speed

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