Why is it difficult to hold a school bag having a strap made of a thin and strong string?
It is difficult to hold a school bag having a thin strap because the pressure on the shoulders is quite large. This is because the pressure is inversely proportional to the surface area on which the force acts. The smaller is the surface area; the larger will be the pressure on the surface. In the case of a thin strap, the contact surface area is very small. Hence, the pressure exerted on the shoulder is very large.
What do you mean by buoyancy?
In what direction does the buoyant force on an object immersed in a liquid act?
What is the importance of universal law of gravitation?
You have a bag of cotton and an iron bar, each indicating a mass of $100\, kg$ when measured on a weighing machine. In reality, one is heavier than other. Can you say which one is heavier and why?
Why does an object float or sink when placed on the surface of water?