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  Force, Physics tutorial

Definition of Force:

A force is a push or pull on the object resulting from object's interaction with another object. Whenever there is interaction between two objects, there is a force on each of the objects. When interaction stops, two objects no longer experience the force. Forces only exist because of the interaction.

All forces (interactions) between objects can be placed into two broad categories:

i) Contact forces, and

ii) Forces resulting from action-at-a-distance

Contact forces are those kinds of forces which result when two interacting objects are perceived to be physically contacting each other. Examples of contact forces comprise frictional forces, normal forces, tensional forces, air resistance forces, and applied forces.

Action-at-a-distance forces are those kinds of forces which result even when two interacting objects aren't in physical contact with each other, yet are able to apply push or pull despite their physical separation. Examples of action-at-a-distance forces comprise gravitational forces. For instance, sun and planets apply gravitational pull on each other in spite of their large spatial separation.

The Newton:

Force is the quantity which is estimated using standard metric unit called as Newton. The Newton is abbreviated by the 'N'. To say 10.0 N signifies 10.0 Newton of force. One Newton is a amount of force needed to provide a 1-kg mass an acceleration of 1 m/s/s. Therefore, following unit equivalency can be expressed as:

1 Newton = 1 kg • m/s2

Equilibrium:

When all the forces which act on the object are balanced, then object is said to be in state of equilibrium. Forces are considered to be balanced if rightward forces are balanced by leftward forces and upward forces are balanced by downward forces. This though doesn't essentially mean that all forces are equal to each other. The two objects are at equilibrium as forces which act on them are balanced; though, individual forces are not equal to each other. 50 N force is not equal to 30 N force.

If the object is at equilibrium, then forces are balanced. Balanced is the main word which is used to explain equilibrium situations. Therefore, net force is zero and acceleration is 0 m/s/s. Objects at equilibrium should have the acceleration of 0 m/s/s. This extends from Newton's first law of motion. But having the acceleration of 0 m/s/s doesn't mean object is at rest. The object at equilibrium is either:

i) At rest and staying at rest, or

ii) In motion and continuing in motion with same speed and direction.

Stable, Unstable and Neutral Equilibrium:

On displacing the body in equilibrium slightly, magnitudes, directions and lines of action of the forces applying on it may all change.

i) Stable equilibrium

This occurs when forces in displaced position act such that they return the body in the original position.

ii) Unstable equilibrium

If the forces act to increase displacement still further, the equilibrium is unstable.

iii) Neutral equilibrium

If body after being displaced is still in equilibrium, the equilibrium is neutral.

Moments:

The turning effect of the force is called as moment. It is the product of force multiplied by the perpendicular distance from the line of action of the force to pivot or point where the object will turn.

When undoing the nut fastened to the screw by hand one realizes that amount of force needed is a lot greater than when undoing same nut utilizing the spanner. Spanner increases distance between fulcrum and line of action of the force, therefore for the same force a greater moment is attained.

Principle of Moments:

Principle of moments expresses that when in equilibrium the total sum of anti clockwise moment is equal to the total sum of clockwise moment.

When the system is stable or balance it is said to be in equilibrium as all forces acting on system cancel each other out.

 In equilibrium

Total Anticlockwise Moment = Total Clockwise Moment

Parallel Forces:

Parallel forces can be in similar or in opposite directions. Sign of the direction can be selected randomly, meaning, taking one direction as positive makes opposite direction negative. Complete definition of resultant is according to the magnitude, direction, and line of action.

R= ΣF=F1+F2+F3+...

Rd= ΣFx=F1x1+F2x2+F3x3+...

Equilibrium of Parallel Forces

Resultant of the number of forces in equilibrium is zero. It thus follows that algebraic sum of moments of all the forces about any point is zero given forces are in equilibrium. It signifies that total clockwise moment of forces about any point = total anticlockwise moment of remaining force about same point.

Newton's Laws of Motion:

First Law of Motion:

The first law of motion is associated to law of inertia, it says that body will stay in rest or in continue motion, unless some external force is exerted on it. OR

Everybody continues the state of rest or of uniform motion in the straight line, unless forced by some external force to perform otherwise. Inertia: It's the property of body by the virtue of which body remains in rest or in continues motion, unless some external force is exerted OR anybody has tendency to oppose external force applied because of the Inertia. This is also known as as Law of inertia.

Second Law of Motion:

Newton's second law of motion expresses that rate of change of momentum is directly proportional to exerted force and occurs in same direction as applied force.

Momentum, p = mass x velocity

Momentum is the property of the body possessed by virtue of mass and velocity. It is the product of mass of the body and velocity.

Newton's Third Law of Motion:

In football, your feet bring the ball in motion. Therefore, forces arise from interactions between systems. This fact is made clear in Newton's third law of motion.

To every action there is an equal and opposite reaction.

Here terms action and reaction means forces as expressed by first and second laws. If the body A applies the force, FAB on body B, then body B in turn applies force FBA on A, such that

FAB = -FBA

So, we have FAB + FBA = 0

Newton's third law deals with two forces, each applying on the different body.

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