Difficulty in starting or stopping motion of a body is due to:

Correct Answer: Inertia

Explanation:

The difficulty in starting or stopping the motion of a body is due to a fundamental property of matter known as inertia.

Key Concepts:

1. Inertia: According to Newton's First Law of Motion, an object will remain at rest or continue to move in a straight line at a constant speed unless acted upon by an external net force. Inertia is the natural resistance of any physical object to any change in its velocity or state of motion.

2. Types of Inertia:
• Inertia of Rest: The resistance of an object to change its state from rest to motion (making it difficult to start moving).
• Inertia of Motion: The resistance of an object to change its state from motion to rest (making it difficult to stop moving).

Why other options are incorrect:

• Momentum: Momentum is the product of mass and velocity. While it measures how hard it is to stop an object already in motion, inertia is the inherent property responsible for resisting any change in motion altogether.

• Gravity: Gravity is an attractive force between two masses, not the internal resistance of a body to changes in motion.

• Friction: Friction is an external opposing force that acts between surfaces in contact, but it is not the intrinsic property of the body itself that resists a change in motion.

Thus, the primary property responsible for the difficulty in starting or stopping motion is Inertia.