Question 1

Which type of friction occurs between two surfaces that are not moving relative to each other?

Accepted Answer

Static friction. Static friction is the force that prevents an object from starting to move on a surface. It is generally the strongest type of friction between two solid surfaces. This force must be overcome for an object to begin its motion.

Question 2

What happens to the frictional force when the roughness of the surfaces in contact increases?

Accepted Answer

It increases. Frictional force increases when the surfaces in contact are rougher due to more interlocking of irregularities. These microscopic peaks and valleys create resistance against relative motion. Smooth surfaces typically experience much lower frictional resistance.

Question 3

Which of the following is used to reduce friction in rotating machine parts?

Accepted Answer

Ball bearings. Ball bearings reduce friction by converting sliding motion into rolling motion. Rolling friction is significantly less than sliding friction for most materials. This technology is widely used in bicycle wheels and fans.

Question 4

Friction is a force that always acts in which direction relative to the motion?

Accepted Answer

Opposite direction. Friction always acts in the opposite direction to the relative motion of an object. It works to resist or slow down the movement of the surfaces. Without this resistance, objects would never stop moving once started.

Question 5

Which of the following substances acts as a lubricant to reduce friction?

Accepted Answer

Oil. Oil acts as a lubricant by creating a thin layer between the moving surfaces. This layer prevents direct contact between the microscopic irregularities of the surfaces. Graphite is another common solid lubricant used in machinery.

Friction — Set 1