What is Circular Motion
When an object moves in a circle, it is called Circular Motion
Example
An athlete taking a round of a circular park
What is Uniform Circular Motion
If an object moves in a circular path with uniform speed, it is called Uniform Circular Motion
Examples
Motion of Moon(Moon Moving around the earth)
Motion of Earth(Earth Moving around the sun)
A cyclist on circular track
What is Constant in Uniform Circular Motion - Speed or Velocity?
In Uniform Circular Motion, speed is constant
As our object keeps on changing direction, velocity keeps on changing.
So,velocity cannot be constant.
Explanation
Let's take different tracks
Rectangular Track
If an athlete travels rectangular track ABCD, he has to change direction 4 times
AB, BC, CD, DA
Hexagonal Track
Similarly in Hexagonal track ABCDEF,
athlete has to change direction 6 times
AB, BC, CD, DE, EF, FA
Octagonal Track
Similarly in Octagon ABCDEFGH
Athlete has to change direction 8 Times
AB, BC, CD, DE, EF, FG, GH, HA
Hence, as number of sides increase
, athlete has to change direction more number of times
Similarly if we keep on increasing sides, it becomes shape of a circle
It can be said that circle contains infinite number of sides
An athlete moving in a circular changes direction infinite number of times
Why is Uniform Circular Motion always called accelerated motion
If a person travels in uniform circular motion, its magnitude of velocity(speed) remains constant
However, direction of motion keeps on changing indefinitely
Hence Uniform Motion is called Accelerated Motion
Example 1
An athlete running in a circular track with uniform speed keeps on changing direction infinite number of times
Since direction keeps on changing,it is accelerated motion
Example 2
A toy train moves in a circular path at constant speed but direction of toy train keeps on changing indefinite number of times
Since direction keeps on changing,it is accelerated motion
How to Calculate Distance and speed in case of Circular Motion
We know that
Circumference of Circle = 2πr
where r is radius of Circle
So Distance travelled by a body moving in a Circular Path
= Circumference of Circle
= 2πr
Example 1
Suppose a person takes a round of circular park whose Diameter is 140 Meters
What is Distance covered by Person
Diameter = 140 meters
Radius = Diameter/2 = 140/2 = 70 meters
Distance travelled by a person =
= 2πr
= 2 × 22/7 × 70
= 440 meters
How to Calculate Speed/Velocity in case of Circular Motion
We know that
Speed = Distance/Time
in Circular Motion,Distance = 2πr ,So
Speed = 2πr / Time
Formula of Velocity is also same
Velocity = 2πr/Time
v = 2πr/t
Example 2
Suppose a person takes a round of circular park whose Diameter is 140 Meters in 2 minutes
What is Distance covered by Person
What is speed of Person
Distance travelled by a person=
= 2πr
= 2 × 22/7 × 70
= 440 meters
Time Taken = 2 minutes = 120 seconds
Formula of Velocity is also same
Velocity = 2πr/Time
v = 2 π r/t
v = 440/120
v = 3.67 meters/second
Direction of Acceleration and Velocity in Circular Motion
In Circular Motion,
- Acceleration is always towards the center
- Velocity is always along tangent
In the figure, we can see the direction of velocity and acceleration at different points in circular motion
