Solids and fluids
Let us now see how we can distinguish solids from fluids.
Def. 1:"Solids have a fixed shape and fixed volume but liquids have a fixed volume but no fixed shape, while gases have neither fixed shape nor fixed volume."
This is a definition that I remember from my schooldays. Perhaps it is in your textbook also. But let us look at it more closely. In Fig. 2, I have shown two pictures of a ball ( made of say rubber, half colored red, half green): Clearly, the ball gets a little squashed when you put it on the table and if you flip it, it is again squashed, but the shape is changed!. So, is it a solid or not a solid? In fact, all materials have finite compressibility, and will deform somewhat under force.