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Differentiate between the following:

(i)   Rest and motion

(ii)  Circular motion and rotatory motion

(iii) Distance and displacement

(iv) Speed and velocity

(v) Linear and random motion

(vi) Scalers and Vectors

Difficulty: Hard

1. Difference between Rest and motion:

Rest:

A body is said to be at rest if it does not change its position concerning its surroundings.

Motion:

A body is said to be at rest if it changes its position concerning its surroundings.

The state of rest or motion of a body is relative. For example, a passenger sitting in a moving bus is at rest because he/she is not changing his/her position concerning the other passengers or objects in the bus but to an observer outside the bus the passengers and the objects inside the bus are in motion

 

2. Difference between Circular and rotatory motion:

Circular motion:

Any turning as if on-axis is rotatory motion. Any rotatory motion where the radius of gyration, length, and axis of rotation is fixed is circular motion. And that is the difference. Circular motion is just a special case of rotatory motion. That is, there is no fixed axis and radius restriction for rotatory motion. But there is circular motion.

For example, all planets have rotatory motion around their suns but most of the orbits are elliptical. Therefore, the rotation axis and radius of gyration vary as they trek around. So, most, if not all, planets do not have circular motion.

 

Note: Gyration length:

A length that represents the distance in a rotating system between the point about which it is rotating and the point to and from which the transfer of energy has the maximum effect.

 

3. Difference between distance and displacement:

Distance

Displacement

Length of the path between two points is called the distance between those points. 

Displacement is the shortest distance between two points which has magnitude and direction distance distance

Distance is a scalar quantified displacement

Displacementquantity distancentity

Distance is denoted by “S”.

            S=vt

Its unit is metered (m). 

Displacement is denoted by “d”.

d=vt

Its SI unit is meter (m).

Distance(S) dotted lines, Displacement(d) dark lines from point A to B.

 

4. Differentiate between speed and velocity

Speed

Velocity

The distance covered by an object in a unit of time is called speed.

 

 Distance=speed x time

 Or

 S=vt

The rate of displacement of a body is called velocity.

 

V=d/t or d=vt

Speed is a scalar quantity.

Velocity is a vector quantity.

SI unit ispeed is

SI unit of velocity is the same as the speed

 

5. Difference between linear and random motion

Linear motion:

The straight-line motion of a body is called linear motion.

Examples:

The motion of objects such as a car moving on a straight and level road is linear motion.

Airplanes flying straight in the air and objects falling vertically down are also examples of linear motion.

 

Random Motion:

The disordered or irregular motion of an object is called random motion.

Examples:

The motion of insects and birds is irregular. Thus, the motion of insects and birds is random.

The motion of dust or smoke particles in the air is also random.

The Brownian motion of a gas or liquid molecules along a zigzag path as shown in the figure is also an example of random motion.

 

 

6. Difference between scalers and vectors:

Scalers

Vectors

A scalar quantity is described completely by its magnitude only. 

A vector quantity is described by its magnitude and direction. 

Examples

Examples of scalers are mass, length, time, speed, volume, work, energy, density, power, charge, pressure, area, and temperature.

Examples

Examples of the vector are velocity, displacement, force, momentum, torque, weight, electrical potential, etc.

 

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