Question

Which of the following statements about friction is wrong?
A) Frictional force can accelerate a body
B) Frictional force can be reduced to zero
C) Kinetic friction is always greater than rolling
D) Frictional force is proportional to the area of contact between the surfaces

Answer 1

Hint: Frictional force is an opposing force produced when there is a contact between the two surfaces and they slide over each other. We can see the properties of friction and check which of the given statements is wrong.

Complete step by step answer:
As friction is an opposing force it resists the motion when two surfaces come in contact with each other. Its properties are:
i) It opposes the direction of motion.
ii) It is independent of the area of surfaces in contact
iii) It depends upon the type and nature of the material in contact (coefficient of friction)
iv) It depends upon the net normal force among the two surfaces
v) It does not initiate motion but respond
vi) It is parallel to those surfaces that are moving with respect to each other.
vii) Order for different types of friction:
static > kinetic > rolling
Checking the options to find which among them is wrong.
A) Frictional force can accelerate a body: Frictional force can cause acceleration but it would be in the opposite direction of the motion.
🡪This statement is true.
B) Frictional force can be reduced to zero: Theoretically, frictional force can be zero for highly polished surfaces, ice, etc. But this isn’t possible in real life.
Thus, this statement is partially true (since not completely wrong).
C) Kinetic friction is always greater than rolling: This statement is true according to the vii) property of friction mentioned.
D) Frictional force is proportional to the area of contact between the surfaces: This statement contradicts the ii) property of friction mentioned here that states its independent of area of surfaces in contact.
🡪This statement is completely wrong.
Therefore, among the given options, option D) stating that frictional force is proportional to the area of contact between the surfaces is wrong.

Note:Friction is caused due to irregularities on both of the surfaces that are in contact.
If one of the two objects lie flat on the other object, then frictional force will be equal to the weight of the object