 # MOTION

WHAT IS MOTION?

Change in the position of the object with respect to the time and surroundings is called motion. For example; position of car with respect to its surroundings is changing, then car is said to be in motion.

• Uniform motion When an object covers equal distances in equal intervals of time is said to be as uniform motion.

For Example:

 Time 9:00 9:10 9:20 9:30 9:40 Distance 10 m 20 m 30 m 40 m 50 m

In uniform motion the nature of the graph is straight line.

• Non-uniform motion– When an object covers unequal distance in equal interval of time is said to be as non-uniform motion.For Example:

 Time 9:00 9:10 9:20 9:30 9:40 Distance 12 18 30 32 40

In Non-uniform motion the nature of the graph is curve.

• REST – when object does not change its position with respect to the time and surroundings.

For example;

• Mountains can be at rest but, if someone observes mountains from space, earth is in motion. Hence, mountains will also be in motion.
• Suppose you are travelling in the bus, then the trees and the shop  appears you moving in backward motion.

This concludes that nothing in the universe is at rest.

What is the difference between scalar and vector quantities?

Scalar – The physical quantity which has only magnitude.

For example; length, mass, time.

Vector– The physical quantity which has both magnitude and direction.

For example; Force(push/pull), weight(mg).

What are the Various Physical Quantities of Motion?

1. Speed: Distance travelled by an object in unit time is called as speed. The SI unit of speed is meter per second (m/s). Another unit of speed include centimeter per second (cm/s) and kilometer per second (km/s).

SPEED = DISTANCE / TIME

Mathematically, V = D/T

where V is the speed of the object.

To specify the speed of an object, we need  only its magnitude. The speed of the object need not to be constant. In most cases, the object will be in non-uniform motion. Therefore, we describe the rate of change of the motion of such objects in term of average speed.

• Average Speed – The average speed is obtained by dividing the total distance travelled by the total time taken. That is, Image Source:

Mathematically, V= S/t

where V is the Average Speed, S is the Distance and t time taken by car.

For example; if the car travels a distance of 100 km in 2 h. Its average speed is 50 km/h.

• Uniform Speed When an object covers equal distances in equal intervals of time is called as the uniform speed.

For example; the car covers 6 m in 3 min then it is said to be as uniform speed.

• Variable Speed – when an object covers unequal distances in equal intervals of time is called as the variable speed.

For Example; while driving a car the driver not maintained a particular speed or when we throw a ball it travels  with different speed because of the forces acting on it.

• Instantaneous Speed – It is calculated as the speed of an object at instant time.

For example; when car travels, it sometimes speeds up or even slows down according to traffic on the road and     sometimes stops when the red light comes. So, the speed which is read from the speedometer at an instant of time is its instantaneous speed.

1. VelocityThe quantity that specifies both direction of motion an object along with its speed is called velocity. It is the speed of an object moving in a definite direction. The velocity can be variable and uniform. It can change by changing the object speed. It can be zero, positive, negative. It is denoted by symbol v headed by the arrow. (arrow represent the vector quantity). Its SI unit is m/s.

The formula is same as the speed that is,  S= D/T

When the object is travelling along the straight line with variable speed then the rate of change of the motion is given by the average velocity.

Then the formula is same as that of average speed that is; average speed = total distance / total time

But, when the velocity of the object is changing at uniform rate, then average velocity is given by the arithmetic mean of the initial velocity and final velocity for given period of time. That is;

AVERAGE VELOCITY = INITIAL VELOCITY+FINAL VELOCITY/2

Mathematically, Vav = u+v/2

Where Vav is the average velocity, u is the initial velocity and v is the final velocity. SI unit is m/s.

1. ACCELERATION – The increase in the change in velocity of the object during any intervals of time is called acceleration. It never zero.

To proof that we have acceleration, which measures the change in velocity of an object per unit time. That is;

ACCELERATION = CHANGE IN VELOCITY/ TIME TAKEN

Mathematically, a = v-u/t

Where a is acceleration, v is final velocity, u is the initial velocity and t is time taken.

Its SI unit is meter per second’s square  (m/s^2).

Uniform AccelerationIt is described as when the object covers equal amount of change in velocity in equal amount of time is called as the uniform acceleration. The motion of the freely falling body is the example of uniformly accelerated motion.

Non-Uniform AccelerationIt is described as when the object covers unequal amount of change in velocity in equal intervals of time is called as the non-uniform acceleration. If the car travelling along a straight road increases its speed in unequal amounts of time, then the car is in non-uniform acceleration.

RetardationDecrease in the change in the velocity of the object in equal intervals of time is called Retardation.

1. DISTANCE – It is the actual path travelled by the object. Distance is a scalar quantity. A device used to measure the total distance is Odometer. Its SI unit is metre(m).
2. DISPLACEMENT – It is a one-dimensional quantity that describes the change in position of the object. It is also called as the straight path which represent the separation between the two different points. It is a vector quantity and has direction and magnitude.

For example;

If the object moves from the position A to B, then the distance travelled is called as the displacement. But, if your starting point and the ending point is the same, then the displacement will be zero.

The displacement is also called as the shortest distance travelled by the object. Displacement cannot be greater than distance.

Its SI unit is same as that of the distance that is metre (m).