# The motion in physics

Moving away from introduction of physics, energy, work done, units and dimension and measurement, today we are going to study motion.

Motion: it the movement of a body from one place to another. The study of motion without involving the force that causes it is called Kinematic, while the study of how force affect motion of body is called Dynamics

## Types of motion in physics

Random motion: it is a movement of an object in no direction. Example of such motion is Brownian motion – an irregular motion of particle of various kind suspended in water, or motion of gas molecule or particle
Translation or linear motion: this is the movement of a body from one point to another; example are – a book sliding from one end of an inclined table , a body running in a straight line from goal post to another or small ball thrown vertically upward.
Rotational motion: it is the movement of a body in a circle, such as rotation of Earth about its axis, rotation of an electric fan blade and a wheel of a moving car.
The Oscillatory /periodic/vibratory motion: it can be defined as to and fro movements of a body. In this type of motion the moving body repeat at successive equal interval of a time. Any motion that repeats itself at a regular interval of time is known as oscillatory motion. Example of such motion are the balance wheel of a watch, vibrating of violin string, rotation of Earth about it axis, simple pendulum and vibrating body on string.

### Concept of motion associated with straight line

A straight line is the shortest distance between two points. These are the concept we need to know concerning motion in the straight line: position, distance, scalars, vectors, and displacement.
Position: the position of a point is described with reference to another point whose position is known. To describe the position of a point in a space, we draw two line perpendiculars to each other at 0

The position of point is determined by two co-ordinate, if we say that the co-ordinate of point p in above diagram, are (x,y), it means that the distance of p from 0 in x-direction is x and y in y- direction. If the point is 4 unit in x-direction and 6 in y-direction, then the co-ordinate of p is (4,6) , similarly Q is (2,4). The straight line pointing P & Q is the distance PQ, which is equal to

$\sqrt { (4-2){ }^{ 2 }+(6-2){ }^{ 2 } } =\sqrt { 8units }$

Scalar quantities: they are the quantities that have magnitude but no directions. Example, energy, temperature, heat etc.
Vector quantities: they the quantities that have both magnitude and direction. Examples; velocity acceleration, force, displacement etc.

#### Relative motion in physics

Relative motion physics is movement of a body in relation to another. Earth is always in motion so we can say that all body moves in relation to Earth. When two bodies moves, the way to handle the relative motion to other is to assume that Earth is at rest. For instance:
Two vehicle P and Q traveling side by side at the same speed, to the passengers at P the vehicle Q is stationary and vice versa. This means that the motion of each vehicle in relation to other is zero.
If P and Q travel in the same direction with speed of 40kmh-1 and 60kmh-1 respectively. The speed of Q in relative to P equal to 60 -40 = 20kmh-1
Consider P and Q moving in opposite direction, then the velocity of Q in relative to P equals to 60+40 = 100kmh-1
Note that, in a case in which the motion of the two bodies are not in a straight line , the relative speed can also be calculated using parallelogram law of forces.

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