1. Weighing machines gives weight not the mass.
2. As far as weight is concerned, cotton is heavier than iron
3. Because, Density of cotton is less than that of iron, so cotton will occupy more space than iron, and hence it displaces more volume of air
4. And since, upthrust is directly proportional to the volume of fluid displaced, cotton will experience more upthrust than iron bar.

Laws of flotation are:
1. The weight of a floating body in a fluid is equal to the weight of the fluid displaced by the body.
2. The centre of gravity of the floating body and the centre of buoyancy are in the same vertical line.
The point through which the force of buoyancy is supposed to act is known as centre of buoyancy.

1. An object will sink or float in a liquid is determined by the density of the object compared to the density of the liquid .
2. If the density of a substance is less than the density of the liquid it will float. For example, a piece of wood which is less dense than water will float on it.
3. Any substance having more density than water for example a stone, will sink into water.

1. Take a nail. It has two ends. One end is sharp and other end is bulged head.
2. We usually keep the pointed end on the wall or wood and hammer on the bulged head
3. So very small area creates a large pressure.
4. Thus the nail penetrates into the wall or wood.

The fish maintains buoyancy. Fishes have the ability to make themselves lighter to float up or heavier to sink down by using its swim bladder. The swim bladder is filled with air it will float.