1. The force acting perpendicularly on a surface is called thrust. The thrust/force acting on unit area of the surface is called pressure. SIunit of thrust is Newton.(N) SI unit of pressure is Pascal.(Pa) Lets know more about thrust and pressure.

2. If we push hard on a piece of wood with our thumb, the thumb doesnt go into the wood But if we push a drawing pin into the wood with the same force of our thumb, the drawing pin goes into the wood. Our thumb doesnt go into the wood because the force of thumb is falling on a large area of the wood due to which the force/area(pressure)on the wood is small .Whereas in the case of drawing pin the area of pin falling on wood is small therefore the pressure is more and pin goes into the wood. Pressure is the force acting on a unit area of the object. 3. We have just defined pressure in terms of force. Pressure can also be defined in terms of another term called thrust. The force acting on a body perpendicularly to its surface is called thrust. Actually, thrust is the total force acting on the surface of a body. 4. When an obj. is placed in a liquid, the liq. exerts an upward force on it . Ex. when a piece of cork is held below the surface of water by applying the force of our thumb and then released, the cork immediately rises to the surface. It appears as if some upward force is exerted by water on the cork which pushes it to the surface. 5. Whenan object is immersed in a liquid, it experiences an upward force. This upward force is called buoyant force. Thus the upward force acting on an object immersed in a liquid is called buoyant force(upthrust) 6. When a solid object is immersed in a liquid, an upward force (upthrust) is experienced which is equal to the weight of liquid displaced by the object. In other words: Buoyant force(upthrust) Weight of acting on an obj. = liquid displaced by that obj. 7. Some substances appear to be heavy whereas others are light. For ex., iron is heavier than aluminium and water is heavier than alcohol. In physics we describe the lightness or heavyness of different substances by using the word density. The density of substance is defined as mass of the substance per unit volume. Density =mass of the substance volume of the substance 8. I got a wonderful knowledge by making this power point presentation as I get to know more about thrust, pressure, density, archimedes principle, etc. I am very thankful to my IT sir and science mam. Thanks