Friction — Set 5

Correct Answer: A. Contact force

Friction is categorized as a contact force because it only exists when two surfaces are physically touching. It arises from the microscopic interactions between the touching surfaces. Gravity and magnetism are examples of non-contact forces.

Correct Answer: B. Surface irregularities

Friction is primarily caused by microscopic irregularities on the surfaces that interlock with each other. Even surfaces that look smooth to the naked eye have peaks and valleys. These irregularities resist the sliding motion between the two objects.

Correct Answer: D. It is opposite to the relative motion

Friction always acts in a direction that opposes the relative motion or the tendency of motion. If you push a box to the right, friction acts to the left. This opposing nature is the defining characteristic of frictional force.

Correct Answer: C. Rolling friction

Rolling friction is usually much smaller than both static and sliding friction. This is why vehicles use wheels to transport heavy loads efficiently. The point of contact in rolling is much smaller and changes constantly.

Correct Answer: B. Contact between surfaces

Friction cannot exist without physical contact between two surfaces or a surface and a fluid. It is the interaction at the interface that generates the resistance. Once the surfaces are separated, the frictional force vanishes immediately.

Correct Answer: A. Lubricants

Lubricants are substances like oil, grease, or graphite used to minimize friction and wear. They form a thin film that keeps the two surfaces from grinding together. Proper lubrication is essential for the longevity of mechanical engines.

Correct Answer: A. Due to air friction

Meteors travel at very high speeds, and the friction with the air (air resistance) generates intense heat. This heat is often enough to vaporize the meteor, creating a 'shooting star'. This is a dramatic example of fluid friction converting kinetic energy into heat.

Correct Answer: D. Production of heat

Friction always results in the production of heat as mechanical energy is dissipated. This can be seen in car tires getting warm after a long drive. If not managed, this heat can cause mechanical failure in high-speed machinery.

Correct Answer: B. It is useful but causes energy loss

Friction is 'necessary' because it allows us to walk and drive, but an 'evil' because it wastes energy and wears out parts. Without friction, we couldn't hold a cup or stop a car. Balancing its benefits and drawbacks is a major task in engineering.

Correct Answer: B. It increases friction

The frictional force is directly proportional to the normal force pressing the surfaces together. Increasing the weight of an object increases the normal force and thus the friction. This is why pushing a heavy couch is much harder than pushing a light chair.