$F=ma$

Forces are used in our daily life actions like pushing, pulling, lifting, twisting etc. So, a force is a pull or push acting on an object which tends to change the state of rest/ motion of an object. An interaction of one object with another object results in a force between the two objects.

For example, Weightlifter uses muscular force to lift the weights.

Hence, At least 2 object must interact for a force to come into play. 

we know that 

Effort is defined as a force exerted by a machine or in a process.

By repeatedly pushing, pulling or dragging a body, we can increase the amount of force applied on that body. Hence option D is correct.

According to Newton's first law, force is the rate of change of momentum.
Therefore, a force is not a physical object that can be seen. However, the effect of a force on an object can be seen (i.e its changing momentum)

Pulling of a cart, stretching of a coiled spring and kicking of a ball take place due to contact forces but weight of the body (gravitational force) is a non-contact force.

The weight of mass of 1 gram of body is

When similar poles of magnets are brought near each other, they tend to repel i.e they push each other away.

To move a loaded cart we have to pull it . Hence action involved is as pulling.

All the above examples can be grouped as push. As force is applied to move object away from the body.

The action involved in moving a book placed on a table can be pulling, pushing or lifting for which force is required.

For moving a loaded cart  and drawing a bucket of water from a well, the action involved is pulling hence can be grouped as Pull.

When one object interacts with another object they exert force on each other, either towards or away from each other.

To open or to shut a door the action of pulling and pushing can be applied.

When a magnet is placed near to the pieces iron, it pulls the pieces of iron towards itself due to it magnetic field action involved is pulling.

Force is required to move a stationary object, to stop a moving object, etc. The phenomenon required to push or to pull on object is force.

For pushing a car, a force is required in the direction of motion of the car. 

When a force can be applied by an object on another only if it is in contact with each other, it is called as a contact force. 

There are two types of force 
1) Interactive force: Its effect comes when two objects will come in contact.
2) Non- Interactive force: Its effect will come when an object comes in their respective field strength.

Force is involved in all kinds of push and pull.

Force always comes into action when there will be interaction between the objects, Here both the teams are exerting force on each other through the rope.

A force when applied on a non rigid object, changes the inter spacing between its constituent particles and therefore causes change in its dimension and can also produce motion in it.

A force when applied on a rigid object does not change the inter spacing between its constituent particles and therefore it does not change the dimension of the object.,but cause only motion in it.

We are to remember that force does not always make an object to move. For example,we may push a large piece of rock without displacing it from its position.We may even push a wall without any success. And, on the other had, we may apply force on a dough by our fingers to change its shape and size. So, a force does not always make an object to move, it may be used to change the shape and size of an object as well.

Force is a vector quantity because it has both magnitude and direction.

Force can change the shape and size of an object-when a force is applied on a soft object, it changes the shape and size of the object.

When a spring is pulled, it's shape and size changes. When a force is applied on a soft object,it changes the shape and size of the object.

Force cannot be seen.we can 'see' or 'feel' the force through its effects.when an inflated balloon is pressed between the two hands,its shape and size changes.

Force acting on a body is a push,pull or a squeeze.

A force is a push or pull on an object. This push or pull comes from the objects interacting with one another and only from such interactions. Once the interaction stops, there is no longer any force.

Force acting on a body can change its state of rest or of motion.

A force can make a stationary object move-when you kick a stationary football,it moves.

A force can stop a moving object-when a force is applied on a moving object in the direction of motion,its speed increases.

$Answer:-$ B

We can infer that at least two objects must interact for a force to come into play.Thus,an interaction of one object with another object results in a force between the two objects.

At least two objects must interact for a force to come into action.

An interaction of one object with another object ,results in a force between the two objects.

The contact forces represent the result of physical contact between two objects,one by which force is exerted and the other on which force is exerted.

Forces are due to an interaction.So the car will only move on application of force.

F = ma

$M=0.4 gm$ $=0.4 kg$

When swimmer apply force on the water , then reaction force act on the man due to water. This force on the man drive man forward in the water.

We know that 

Interatomic  force  constant
$= Y \times inter\ atomic \ distance$
$ = 2\times 10^{11} \times 2.8\times 10^{-10}$
$ = 2\times2.8\times 10$
$ = 56 N/m$

The SI unit of force is the newton, symbol N. The base units relevant to force are: the metre, unit of length, symbol m, the kilogram, unit of mass, symbol kg, the second, unit of time, symbol s.

Since neither force nor couple on body is zero, thus it is non-degenerate wrench.

Newton (N) is a SI unit of Force while dyne is a CGS unit of force.   

Newton's first law of motion represents the qualitative measure of force.It states that:

First law of motion: