Question

Gas exerts pressure on the walls of container because the molecules-
(A) Are losing the kinetic energy
(B) Are getting stuck to the walls
(C) Are transferring their momentum to the walls
(D) Are accelerated toward walls

Answer 1

The substances that have the ability to flow are called fluids; gas is fluid as it has no fixed shape and has very low density. The pressure at a point is the force acting per unit area of the surface around that point. The molecules of a fluid collide with the walls due to their random motion and thus suffer a change in momentum. So by eliminating the wrong options, one can find out the correct answer.

Complete step by step answer:
Amount of pressure acting at a point, $P = \dfrac{F}{A}$
where $P =$ pressure, $F =$ force at that point and $A =$ area of surface around that point.
All the molecules of fluid are always in a state of random motion. During their motion, they collide with the walls of the container or any other surface which comes in their way. They suffer a change of momentum on collision.
Now, according to newton’s second law of motion, force is defined as the rate of change of
momentum. That’s why these molecules experience a force and in turn exert equal and opposite force on the walls of the container.
So pressure can also be defined as the rate of change of momentum per unit area of the surface.
Thus, gas exerts pressure on the walls of the container because the molecules are transferring their momentum to the walls.

Hence, option (C) is the correct answer.

Note: The gap between the molecules in a gas is high, the molecules in a gas are in continuous motion and move randomly in the container in which the gas is stored and thus exert pressure at the walls.
The force exerted on the walls of the container is called thrust. Fluids exert the thrust normally on the surface in contact.
S.I. the unit of pressure is $N/{m^2}$ or Pascal. The pressure is a scalar quantity.