Q: What is friction?

A: Friction is a force that opposes the relative motion between two surfaces in contact.

Q: What factors does the force of friction depend on?

A: The force of friction depends on the nature of the surfaces in contact.

Q: What is combustion?

A: Combustion is a chemical process in which a substance reacts with oxygen to give off heat and light.

Q: What do you mean by ignition temperature?

A: The lowest temperature at which a substance catches fire is called its ignition temperature.

Q: What causes friction?

A: Friction is caused by the irregularities on the two surfaces in contact.

Q: Does frictional force act even when there is a very smooth surface? How does it happen?

A: Yes, even when the surface is smooth, the frictional force is present due to the presence of a large number of minute irregularities on it.

Q: Describe how the force of friction acts between surfaces.

A: All surfaces have minute irregularities on them. These irregularities on the two surfaces lock into one another, and when we attempt to move anything over a surface, we have to apply a force to overcome these interlockings. Thus, the force of friction acts upon the surfaces.

Q: Is friction the same for all surfaces?

A: No, friction is not the same for all surfaces. Rough surfaces have more friction than smoother ones.

Q: Explain how friction is an essential evil.

A: Friction is essential as it allows us to write with a pen or pencil, prevents objects from moving endlessly, and enables the construction of buildings. However, it is also considered an evil as it causes wear and tear of materials.

Q: Which force of friction acts in the opposite direction of motion?

A: The force of friction acts in the opposite direction of motion.

Q: Which substance is used to reduce friction?

A: Lubricant is used to reduce friction.

Q: Which of the following is not a property of friction?

A: Friction does not depend on how hard the two surfaces are pressed together.

Q: Which type of friction has the least force?

A: Rolling friction has the least force.