Test: Force and Pressure -1 (UPSC Level) - UPSC MCQ

A push or pull on an object is defined as a contact force. Contact forces are interactions that occur when two objects are in direct physical contact with each other. These forces can either be attractive or repulsive and are essential in understanding how objects interact with each other in the physical world. For example, when you push a door to open it or pull a chair out from under a table, you are applying contact forces to those objects.

Let's analyze each statement:

1. A force can change the direction of a moving body.
This statement is correct. A force applied to a moving body can alter its direction. For example, when a bat hits a moving ball, the direction of the ball changes due to the force exerted by the bat.

2. Muscular force is a type of force that depends on gravitational pull.
This statement is incorrect. Muscular force is generated by the action of muscles and is not dependent on gravitational pull. It is an internal force produced by the contraction of muscles, used in various activities like lifting, pushing, or pulling.

3. The net force applied in opposite directions is given by the sum of the two forces.
This statement is incorrect. When forces are applied in opposite directions, the net force is actually the difference between the two forces, not the sum. If two forces are equal and opposite, they cancel each other out, resulting in a net force of zero.

Thus, only statement 1 is correct. Therefore, the correct answer is Option A: 1 Only.

1. Pushing a door to open it - This action involves a push force, not a pull force. Therefore, this pair is incorrectly matched.

2. Pulling a rope during a tug-of-war - This is correctly matched as it involves a pull force, where the object (rope) is moving towards the applier of the force.

3. Kicking a football - This involves muscular force as it is the muscle action that kicks the ball. Gravitational force refers to the force acting due to gravity, which is not primarily responsible for the action of kicking. Therefore, this pair is incorrectly matched.

4. Lifting weights during exercise - This is correctly matched as it involves muscular force, where muscles exert force to lift the weights.

Based on the analysis, two pairs are correctly matched: pair 2 and pair 4.

Both Statement-I and Statement-II are correct. Statement-I defines force as a push or pull on an object, which aligns with the definition of force. Statement-II further explains that force can change or tend to change the state of rest or uniform motion, the direction of motion, or the shape or size of a body, which clarifies the various effects of force. Thus, Statement-II logically explains Statement-I, making Option A the correct choice.

The correct answer is Option A: Frictional force. Frictional force is always opposite to the direction of motion between two objects in contact moving with respect to each other. It depends on the nature of the surface in contact and acts as an opposing force that hinders the motion of objects across each other. This force is essential in various everyday scenarios, such as walking, driving, or sliding objects on a surface.

1. Frictional Force: The given description is correct. Frictional force acts between surfaces in contact and always opposes motion. This pair is correctly matched.

2. Magnetic Force: The description provided is incorrect. Magnetic force acts between magnets or a magnet and a magnetic material, and it can be both attractive and repulsive. However, the description here incorrectly refers to it as a force between electric charges, which is characteristic of electrostatic force. This pair is incorrectly matched.

3. Electrostatic Force: The description is correct. Electrostatic force is due to electric charges and can be both attractive and repulsive, as seen when a charged balloon attracts small pieces of paper. This pair is correctly matched.

4. Gravitational Force: The description is correct. Gravitational force is a force that acts between objects due to their mass and is always attractive, as seen in the gravitational attraction exerted by the Earth. This pair is correctly matched.

Pairs 1, 3, and 4 are correctly matched, while pair 2 is incorrectly matched. Thus, the correct answer is Option C: Only three pairs.

Statement-I is correct because frictional force indeed acts between two moving objects in contact, which is a fundamental characteristic of friction. However, Statement-II is incorrect because the frictional force does not solely depend on the nature of the surface in contact; it also depends on factors such as the normal force between the surfaces, roughness, and other environmental conditions. Friction is a result of the interaction between the surfaces in contact rather than just the nature of the surfaces themselves. Hence, while Statement-I is accurate, Statement-II oversimplifies the factors influencing frictional force.

Drinking from a straw works because the atmospheric pressure outside the straw decreases, creating a pressure difference as compared to the higher atmospheric pressure inside the straw. This pressure difference allows the atmospheric pressure to push the liquid into your mouth once you create lower pressure by sucking.

Magnetic force is: 
Non-contact force: Magnetic force can act at a distance without direct physical contact between objects. For instance, magnets can attract or repel each other through space.
Therefore, the correct answer is: B: non-contact force
This is because magnetic forces operate through fields, allowing them to exert influence without needing physical contact.

Statement-I is correct because it correctly defines the pressure due to a liquid column. The formula p = hrg is a fundamental concept in fluid mechanics.
Statement-II is incorrect because while it is true that water and gas exert pressure on the walls of their container, this statement does not directly relate to the formula provided in Statement-I which discusses pressure due to the height of a liquid column.