Force may be defined as a pull or push which produces or tends to produce,stops or tends to stop the motion of a body.e.g.,
(i) To move a football,we have to exert a push i.e.,kick on the football.
(ii) To stop football or a body moving with same velocity,we have to apply push in a direction opposite to the direction of the body.
(iii) A man is trying to move a wall but fails to displace it.
(iv) To change the direction of motion of moving body along a straight line we have to apply a sideways push or pull on it.
Thus,the push or pull which changes or tends to change the state of rest or uniform motion of a body along a straight line is called force.
Force is vector quantity.
Units of force
(i) S.I.System:S.I.unit of force is newton or kg ms-2.
(ii) C.G.S.System: C.G.S unit of force is dyne or g cm s-2.
(iii) Gravitational unit: Gravitational unit of force is kgf.
1N = 105 dyne
1kg F =9.81 N = 981dyne
Composition and resolution of forces :
(1) Composition of forces: The determination of a force whose effect is the same as that of two or more forces acting simultaneously at the same point is called composition of forces,and this single force which produces the same effect as number of individual forces together produce is called resultant force.
or
The process of determination of resultant when a number of forces are acting simultaneously on a body is called composition of forces.
Resultant force
If a number of forces are acting simultaneously on a body,then a single force which can produce the some effect in the body as is done by all the forces together is called resultant force.It is represented by R.
We know that force is vector quantity and vectors cannot be added by using laws of algebra, therefore for the addition of two or more forces acting.Simultaneously on a body we follow some laws,a few of them are given below:
(1) Triangle law
(2) parallelogram law
(3) Method of components
(4) Polygon law.
Dimensions:
A distance may be measured any units i.e.,miles,metres,centimetres,it is a distance.We say that it has dimension in length.Similarly a physical quantity which can be measured in units of mass is said to have dimensions in mass.
Definition of dimensions: The dimensions of a derived physical quantity may be defined as the powers to which fundamental units must be raised to represent it completely.
(i) Velocity = distance/time = length/time = [L]/[T] = [MoL1T-1]
Therefore velocity has dimensions zero in mass,1 in length and - 1 in time.
(ii) Acceleration = velocity/time = length/(time)2=[L]/[T2] = [MoL1T-2]
Therefore Acceleration has dimensions zero in mass,1 in length and -2 in time .
(iii) Force = mass*acceleration =[M]*[L]/[T2]=[M1L1T-2]
Therefore force has dimensions 1 in mass,1in length and-2 in time.
(i) To move a football,we have to exert a push i.e.,kick on the football.
(ii) To stop football or a body moving with same velocity,we have to apply push in a direction opposite to the direction of the body.
(iii) A man is trying to move a wall but fails to displace it.
(iv) To change the direction of motion of moving body along a straight line we have to apply a sideways push or pull on it.
Thus,the push or pull which changes or tends to change the state of rest or uniform motion of a body along a straight line is called force.
Force is vector quantity.
Units of force
(i) S.I.System:S.I.unit of force is newton or kg ms-2.
(ii) C.G.S.System: C.G.S unit of force is dyne or g cm s-2.
(iii) Gravitational unit: Gravitational unit of force is kgf.
1N = 105 dyne
1kg F =9.81 N = 981dyne
Composition and resolution of forces :
(1) Composition of forces: The determination of a force whose effect is the same as that of two or more forces acting simultaneously at the same point is called composition of forces,and this single force which produces the same effect as number of individual forces together produce is called resultant force.
or
The process of determination of resultant when a number of forces are acting simultaneously on a body is called composition of forces.
Resultant force
If a number of forces are acting simultaneously on a body,then a single force which can produce the some effect in the body as is done by all the forces together is called resultant force.It is represented by R.
We know that force is vector quantity and vectors cannot be added by using laws of algebra, therefore for the addition of two or more forces acting.Simultaneously on a body we follow some laws,a few of them are given below:
(1) Triangle law
(2) parallelogram law
(3) Method of components
(4) Polygon law.
Dimensions:
A distance may be measured any units i.e.,miles,metres,centimetres,it is a distance.We say that it has dimension in length.Similarly a physical quantity which can be measured in units of mass is said to have dimensions in mass.
Definition of dimensions: The dimensions of a derived physical quantity may be defined as the powers to which fundamental units must be raised to represent it completely.
(i) Velocity = distance/time = length/time = [L]/[T] = [MoL1T-1]
Therefore velocity has dimensions zero in mass,1 in length and - 1 in time.
(ii) Acceleration = velocity/time = length/(time)2=[L]/[T2] = [MoL1T-2]
Therefore Acceleration has dimensions zero in mass,1 in length and -2 in time .
(iii) Force = mass*acceleration =[M]*[L]/[T2]=[M1L1T-2]
Therefore force has dimensions 1 in mass,1in length and-2 in time.