Question

Which of the following is NOT a non-contact force?
${\text{A}}{\text{.}}$ Magnetic force
${\text{B}}{\text{.}}$ Electrostatic force
${\text{C}}{\text{.}}$ Gravitational force
${\text{D}}{\text{.}}$ Muscular force

Answer 1

Hint: Here, we will proceed by mentioning the major difference between contact forces and non-contact forces. Then, we will mention some of the examples which fell in each of these categories (especially including those mentioned in the options).

Complete step-by-step answer:

A force is any action that can change an object's motion while unopposed. In other words, a force will cause an object with mass to change its velocity, i.e., to accelerate. Force can be rationally described as a push or a pull, too. A force has both direction and magnitude.

The force that acts upon an entity without physically coming into contact with it is called non-contact force. Weight is a very common example of a non-contact force. A contact force, by contrast, is a force applied by another body to a body that is in contact with it.

Contact forces- The forces acting on bodies when they are in physical contact are known as contact forces.

Contact Forces Examples:

1. Frictional force- As a body slides (or rolls) over a rough surface, a force tends to act on it, along with the surface in contact, in a direction opposite to its motion. This force is known as Frictional force.

2. Normal reaction force- The body exerts a force equal to its weight on the surface when it is put on a surface, but the body does not move or fall because the surface exerts an equal and opposite force on the body that is normal to the surface. That force is known as the normal reaction force.

3. Tension force- If a body is suspended by a string, the body pulls the string vertically down due to its weight W, and the string in its stretched state pulls the body upwards by a force which balances the body's weight. This force is known as the tension force in the string (T).

Non-Contact forces- At a distance the forces experienced by bodies even without being physically affected are called the Non-Contact forces.

Non-Contact Forces Examples:

1. Gravitational Forces- The force of Gravity is called the force on a body due to the gravitational pull of the Earth. All the particles in the universe attract each other because of its mass.

2. Electrostatic force- These are the forces which are responsible for the repulsion between two like charges (i.e., two positive charges or two negative charges) and the attraction between two unlike (or opposite) charges (i.e., one positive charge and another negative charge).

3. Magnetic Force- The force between the magnetic poles is called the Magnetic Force. The two like magnetic poles (i.e., both north poles or both south poles) repel each other and two unlike magnetic poles (i.e., one north pole and another south pole) attract each other.

Therefore, clearly from the above discussion we can see that magnetic force, electrostatic force and gravitational force are all three non-contact forces. The only left force is muscular force. This means that muscular force is not a non-contact force.

Hence, option D is correct.

Note- Spring force is also an example of contact force. If one end of a spring is fixed and the other end of the spring is being displaced. Due to this a force acts on the spring which is directly proportional to its displacement and is exerted in a direction opposite the displacement direction. This force is known as the spring force or restoring force.