Basic definition
1.Rigid body:
A body is said to be rigid,if the relative positions of any two particles do not change under the action of the forces acting on it.
2.Mass:
The quantity of matter contained by a body is called mass.
The mass of a body will not change unless the body is damaged and part of it is physically separated.
If a body is taken out in a spacecraft, the mass will not change, but weight may change due to the change in gravitational force.
Mathematically
F= ma
⇒ m= F/a
3.Weight:
Weight is the force with which body is attracted towards the centre of earth.
Or
The weight of the body is defined as the gravitational force exerted on it due to earth.
4.Length:
Length is a physical quantity which is used as a concept to measure linear distances. Actually meter is the unit of length.
5.Time:
The time is a physical quantity which is the measure of successional of events. The successive event selected is the relation of earth about its own axis and this is called a day.
3.Weight:
Weight is the force with which body is attracted towards the centre of earth.
Or
The weight of the body is defined as the gravitational force exerted on it due to earth.
4.Length:
Length is a physical quantity which is used as a concept to measure linear distances. Actually meter is the unit of length.
5.Time:
The time is a physical quantity which is the measure of successional of events. The successive event selected is the relation of earth about its own axis and this is called a day.