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Motion

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 Sub Topics You will be observing many interactions around you every day, like a boy running, bus moving, fruit falling from a tree, a bullet fired etc. You could find it amazing when you start thinking how the body moves! It can either be a small movement or swift, but movement happens. This change in position of an object is called Motion. A body tends to continue in its motion at a constant velocity until and unless an outside force acts on it.It can be visualized using concepts like distance, displacement, speed, velocity, Newton's law of motion, uniform motion, Angular motion, linear motion, rotational motion etc. So let’s go through some of these things.....

What is Motion?

A motion simply tells about a moving body. It is the changing position of a body at a given time. It also explains about how the action happens and laws behind it when a body moves. One must apply an external force to disrupt the balance
Let us check a few examples:

1) A boy kicks a soccer ball and it changes its position and moves to some point.
2) A Boy running in a competition
3) Birds flying in the sky
4) A bike moving when accelerated.

Are Rest and motion Relative?
Yes it is! Rest and motion are always relative terms. Assume that you are sitting in a train. The passenger next to you finds you at rest but the person standing outside the train finds you in motion.

Types of Motion

You can classify motion into two types based on the distance covered:
1) Uniform motion
2) Non uniform motion

Uniform Motion: A body moving in a straight line it talks about the consistency in motion at a given time. If we shorten the time given into equal intervals, each interval will be covering equal distance.

Non uniform motion: Here the distance covered varies for a given time. If we take equal time intervals the distance covered in one interval varies from the other. Therefore the consistency is not maintained.

Equations of Motion

The body is in motion having initial velocity u, final velocity v, displacement s acceleration a for time t. The equations of motion are
These equations are useful for solving the problems of motion.

Motion Graphs

Basically Motion graphs are so many and says lot more about the nature of concepts like speed, velocity, acceleration, displacement etc. Lets us see some often used graphs in motion.
For a body at rest:

For a body in motion:

Uniform motion:

Non uniform motion:

Distance and Displacement

Distance and displacement often give a similar feeling, but that’s not the case. Distance is the scalar measure of an actual path taken by a body from initial point irrespective of any direction to reach its destiny.

Displacement is the measure of how far a body moves from an initial point and is always directed to the finishing point. Both are Distance and Displacement is expressed in meters (m).

Newton's Law of Motion

There are three laws stated by Sir Isaac Newton that relate to force and motion called as Newton's law of Motion:
The first law states that every object tends to remain at rest or in motion at a constant velocity, unless it is acted by an external force. The tendency to resist changes unless an external force is applied is called inertia.

The second law gives the relationship between the force, mass and acceleration. ‘F’ on an object is equal to the mass ‘m’ of that object multiplied by the acceleration vector ‘a’ of the object. F = ma.

The third law states when one body exerts a force on a second body, the second body simultaneously exerts a force equal in magnitude and opposite in direction on the first body.

Angular Motion

Angular motion is the change in angle which happens when the motion is in a circular path. It affects speed, velocity and acceleration of the moving body. If $\theta$ is the angular change when displacement occurs from one point to another in a circular path.

Then the angular speed is

Here $\theta$ is the angular displacement and t is the time taken. They are expressed in radians per second, revolutions per second and radians per second.

Linear Motion

Here $\omega$ is the angular speed and r is the radius of circular path.
Here I is the moment of inertia and $\omega$ is the angular speed.