Question

Force acting per unit area is
A) Acceleration
B) Pressure
C) Velocity
D) None

Answer 1

Hint: The force on a body can be in any direction with respect to the surface. However, the force that acts normal to the surface is measured as a different physical quantity. It is measured as the ratio of the total force acting normal to a surface to the total surface area. The force normal to the surface is also called thrust.

Formula used:
$P=\dfrac{F}{A}$

Complete step by step answer:
The force that acts normal to a surface is often measured with a different physical quantity by finding out the ratio of the total normal force on the surface to the total surface area. This quantity is known as pressure.
Pressure is the ratio of the normal force or thrust on a surface acting per unit area of the surface.
The pressure $P$ on a surface is related to the normal force $F$ acting on it and the surface area $A$ as
$P=\dfrac{F}{A}$
The SI unit of pressure is Pascal $\left( Pa \right)$ where
$1Pa=1N/{{m}^{2}}$
Therefore, the correct option is B) Pressure.
Additional information:
There are also other units of pressure such as bar, atm and torr.
$1atm=1.01325\times {{10}^{5}}Pa$
$1bar={{10}^{5}}Pa$
$760torr=1atm=1.01325\times {{10}^{5}}Pa$

Note:
Students often think that pressure is a vector quantity since force is a vector quantity. However, this is not true as pressure, even though it has a specified direction (normal to the surface) depends upon the orientation of the surface and does not have an independent direction. For determining the pressure, we take the component of the force normal to the surface in the calculations and hence, if the orientation of the surface changes, the component of the force normal to it will also change and so will the pressure. Therefore, pressure is a scalar quantity.