What is a FORCE?
Force is that can change the state of an object. Like, A rested body into the motion & a motion body into the rest body.
Moment of Force
Rotational & Translational Motion
A force when acted on a rigid body, will show two kinds of motion:-
(i) Rotational Motion
(ii) Translational Motion
(i) Rotational motion:- When a body is pivoted at a point and we apply force the body will rotate about its axis through the pivoted point is known as Rotational Motion. (e.g. A wheel is pivoted at its center and when the force will apply, it will rotate about its axis.)
(ii) Translational motion:- When we apply force on a body that is free to move, it will start moving in the direction where the force is applied, which is known as Translational Motion or Linear Motion. (e.g. A football, free to move everywhere we apply the force, which direction we want to send we will kick it and, it will go there.)
What is a Torque?
Factors affecting torque:-
(i) Magnitude of force applied, &
(ii) The perpendicular distance from the pivoted point.
Units of Torque:-
(i) { Unit of moment of force = Unit of force x unit of distance }
(ii) S.I unit of force is { newton x meter }(iii) CGS unit is { gf x cm }
Here, you can see the figure of TORQUE. In this figure point (O) is a pivoted point, point (A) is that point where the force is applied & point (P) is the perpendicular distance from the point(O) & point(A). When we apply the force from point(A), it will make the maximum turning effect on the body and this effect is known as Torque (moment of force).
Example:- A ball is placed on a table it is in rest. When we will apply the force on the ball it will start moving in the direction of the force applied. Then, the ball is said to be in motion.Similarly, if we throw a ball forward, then that ball will stop after going some distance due to the force of friction.
CLOCKWISE & ANTICLOCKWISE MOMENT
Clockwise moment:- The effect on the body to rotate clockwise, the moment of force is called clockwise moment and it is taken negatively.
Ex:- A steering wheel is pivoted at a point and when we apply force on the left side of the wheel in an upward direction & from the right side of the wheel in the downward direction, it will move in the right direction which is known as clockwise moment and it will be negative.
Anticlockwise moment: - The effect on the body to rotate anticlockwise, the moment of force is called anticlockwise moment and it is taken positively.
Ex:- Like the clockwise moment but it will be opposite of clockwise moment, A steering wheel is pivoted at a point and when we apply force on the left side of the wheel in downward direction & from the right side of the wheel in the upward direction, it will move in the left direction which is known as anticlockwise moment and it will be positive.
COUPLE
Single force cannot cause rotation, Rotation is always produced by two equal & opposite forces. In the coupling force the force of reaction at a pivoted point will be equal in magnitude but in the direction to the opposite applied force. The reaction of the pivoted point will be zero.
Ex:- A water tap you cannot rotate a water tap by a single force you have to use the coupling force. Likewise, From one finger you will be unable to rotate the tap, you have to use your second finger to open the tap.
Moment of a couple
(e.g. BY ANTICLOCKWISE BAR) If a bar PQ and the pivoted point of that bar is point (O). Then the moment of force will be:-
=moment of force (F) at the end (P)
= F * OP
=moment of force F at end B
= F * OQ
Total moment of couple (i.e., moment of both the forces) = F * OP + F * OQ
= F * (OA + OB) = F * AB
= F * d
Thus, Moment of couple = Either * Perpendicular distance between the two forces (or couple arm).
Equilibrium of Force
When many forces cannot affect the state of a body and produce no change in its motion or rest body is said to be in the equilibrium of force.
Kinds of Equilibrium
Static Equilibrium:- When a body remains in a state of rest after applying the several types of forces is known as Static Equilibrium
Ex:- Two cars named {A & B} is cars with the same power and capacity pulling each other, no work will be done. Because the force of both cars is equal, then it is said to be Static Equilibrium.
Dynamic Equilibrium:- When a body remains in the state of motion under applying many forces on the body, is known as Dynamic Equilibrium.
Ex:- Like an airplane is flying at a constant height when upward lift on it balance its weight downwards, after applying several forces it is in linear motion is known as Dynamic Equilibrium.
Conditions of Equilibrium of Force
1. The resultant of all forces acting on the body should be zero.
2. The sum of the anticlockwise moments about the axis of rotation must be equal to the sum of the clockwise moments about the same axis.
Principal of Equilibrium
According to the principle of moments in equilibrium:
Sum of the anticlockwise moments = Sum of the clockwise moments
Ex:- Hang a 10cm scale by a string from the middle part of the scale named point (O) and place the equal weight on both sides (A & B) of the scale, and put 5kg of weight on the point (A) on the point (B) place 5kg of weight. The position of the scale will be straight because the weight (A) is equal to the weight (B). This is known as the principle of equilibrium.
Centre of Gravity
The Centre of Gravity is that point where the algebraic sum of the moments of the weight of all the particle's body is zero. The entire body weight becomes zero and considers an act to at this point of the body, anyhow the body is placed. This is known Centre of Gravity.
Ex:- Take a rectangular shape scale {length of the scale is 1 meter} put it on the knife-edge and where ever the scale become stable that point will center of gravity of the scale.
Note able point
1. The position of the center of gravity of the given mass depends on the shape of the body. (e.g. take a straight rod at the time the center of gravity is on the middle of the rod & when you will bend the rod the center of gravity will be on the other point.)
2. The center of the gravity of round shaped body which is hollow from inside is present in the hollow body where there is no material. (e.g. like a circular ring that is hollow from inside the center of gravity will be present on the middle part of the ring where there is no material.)
3. We can be taken as a point particle of weight W at its center of gravity.
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