CBSE Class 9 Answered

Pressure is the force per unit area. ie

pressure = force / area

In SI units, pressure is measured in N/m^2 and is called a Pascal, more commonly used as MPa or Mega Pascals (one million pascals).

Force is measured in Newtons (N)

 

Thrust is Force. Though thrust is force, we use this term in the case of fluids only and we do not use this for solid objects.

If a solid object of mass m is at rest on a surface, and the contact surface area is A. The force acting on that area is mg, the weight of the object. Whatever the shape of the object, the force acting on the area of contact will be the same as the weight of the object.

In the case of liquids, it is different, the force that is acting on the contact area is not termed as force, and instead it is called thrust to differentiate the force acted on by a solid. Whatever is the area of contact the thrust (force) is determined not by the weight of the liquid over it, but it is determined only by the vertical water height (and density) of the liquid.

In the case of solids, the force acting per unit area is called stress and in the case of fluids the thrust acting on unit area is called pressure.

The pressure at any point inside a liquid on a horizontal surface will be the same, whereas the stress (pressure) at a point on a horizontal surface of a solid will be different at different points.