Contact forces and non-contact forces - class-VIII

Between two conducting plates, there is the uniform electric field and therefore the same charge is applicable on both proton and neutron. Since Proton mass is more than that of the electron, it will have less acceleration and hence less speed achieved by it. Therefore electron will reach plate with larger velocity.

Electrostatic repulsion = $F _e=\dfrac{1}{4 \pi \epsilon } \dfrac{q^2}{r^2 }=\dfrac{1}{4 \pi \epsilon } \dfrac{4e^2}{r^2 } $

gravitational attraction = $ F _g = G\dfrac{m^2}{r^2} $

$\dfrac{F _e}{F _g} = \dfrac{1}{4 \pi \epsilon } \dfrac{4 e^2}{G m^2} = 3.1 \times 10^{35} $

In electrostatic force, the force of medium depend on charges while the force of medium due to gravity does not depend on masses. There is no concept of induced mass.

The electric force between two electrons is $F _e=\dfrac{ke^2}{r^2}$

Due to electrostatic force clothes tends to stick to our body. 

When object is rubbed with some materials it acquires charges. This object is called as charged object and develops electrostatic force.

Gravitational force is an attractive force as it tends to move all objects towards itself.

Objects tend to move downwards to the earth because of gravity of the earth. This force, exerted on the object is known as force of gravity. 

Gravity is not a property of the earth alone. Every object in the universe exerts a force on every other object. This is called gravitational force. Naturally, moon also has its own gravity.

Answer is B.

Gravity is a very, very weak force. In a hydrogen molecule it pulls the two protons together with a force about 36 powers of ten weaker than the electric force between them.
Therefore, on small scales (within an atom/molecule), the other forces are much stronger, but on larger scales, it seems that gravity is a far stronger force; e.g. planets are held to the sun by gravity. 
Hence, among the given options, gravitational force is the weakest.

A non-contact force is a force applied to an object by another body that is not in direct contact with it. The most familiar example of a non-contact force is weight.

In screws the direction of force applied is perpendicular to the wall and due to its cuts present their is a force applied tangential to the wall which helps in easy movement of the screw.

Coulomb electrostatic force of attraction acts between the two bodies which are separated by a finite distance, hence it is non contact force since the two bodies need not to be in contact with each other whereas the rest of the forces are contact forces.

$r=1fermimeter$ which is same for all.
$F _e=\frac{k _eq _1q _2}{r^2}  ;F _g=\frac{Gm _1m _2}{r^2}$ ; 
$F _N=\frac{\alpha}{r^2}$
where$k _e=8.988\times10^9 N^2m^2c^{2} $;
$q _1=-1.6\times10^{-19}c$; 
$q _2=1.6\times10^{19}$;
$G=6.67\times10^{-11}m^3kg^{-1}s^2$;
$m _1=9.1\times10^{-31}kg$; 
$m _2=1.67\times10^{-27}kg$;
$\alpha=2.3103\times10^{-28}$
$F _e=2.307\times10^{-28}$  ; ${F _g}=1.868 \times10^{-64}$ ;
$F _N=2.3103 \times10^{-28}$
hence,$F _N>F _e>F _g$

Answer is C.

The force of gravity is the force with which the earth, moon, or other massively large object attracts another object towards itself. Gravitational force exists between all the bodies having mass in the universe.

Gravitational force acts at a distance. Therefore it is a non-contact force.

A force applied on an object without any contact it is non-contact force, Examples are magnetic force, electrostatic force etc.

Magnetic force and electrostatic forces are non-contact force as the force applied on an object without any contact with it, similarly, with gravitational force this is force applied without being aware of it and all time.

Unlike poles of the two magnets attracts each other. the force applied by it is non-contact forces and magnetic force.

Like poles of two magnets repel each other, The force between them is non contact force and magnetic force

Being hit by a bat, muscular force acts on the  ball. And, all the bodies on the earth are acted upon by  the gravitational force. So, the ball is acted upon by both muscular and gravitational force.

Gravity is not a property of the earth alone. Every object in the universe exerts a force on every other object. This force is known as the gravitational force.

The attraction or repulsion can also be referred as pull or push force between two objects.

Electrostatic force is a exerted by a charged body on another changed or uncharged body.

Gravitational force is a non-contact force. For action of gravitational force, contact with an object is not required. The force of gravity acts on all object at all the time even while not in contact with the earth.

The attraction and repulsion between charged objects happen due to the action of electrostatic forces. Electrostatic force act between bodies not in contact. So, attraction and repulsion between charged objects are examples of non-contact force.

To ride a cycle, you are to apply muscular force on the pedals of the cycle. The tyres of  the moving cycle are acted upon by the force of friction from the road. And, all objects on the earth are acted upon by the gravitational force.

Objects tend to fall downward towards the earth as the earth pulls the objects due to its gravity. The pull is known as gravitational force.

In electrostatic force, force is exerted by an object on another object not in contact.

Tension force, normal force and air resistance force act on the objects which are in physical contact (touch) with each other and thus all these forces are often called as contact forces.

Magnetic force, electric force and gravitational forces are non contact forces because for these forces to apply, the bodies need not be in contact (physically touch) with each other.

It is not necessary for the two objects to be in contact (touch) with each other to exert gravitation force, magnetic force and electric force. These three forces can be exerted even if the two objects are separated by a finite distance. Thus these forces are non-contact forces.

Earth and Fruits.
Here Force of gravity acts between the fruits and earth.
And due to this the fruit detached from the tree falls to the ground due to Force of gravity.

When boy throws a ball down only gravitational force will act, as electrostatic force act between two charge particle , so there is only gravitational force that is acting on ball. 

Friction is a surface phenomenon. When two surfaces have irregularities that come in contact do they get interlocked  preventing them against sliding against each other. So, frictional force is a contact force dependent on surface.
Here, option (B) is correct. 
Gravitational force, electrostatic force and magnetic force does not depend on the surface.