Short Question Answers
1. Why do clouds seem to be floating in the sky?
Since clouds are tiny particles of water, the upthrust force acting on the clouds and viscous force on it balances its weight. So, the cloud particles gain terminal velocity and move with a constant speed in the sky. Therefore, they seem to be floating in the sky.
2. Why is the bottom of the ship made heavy?
When the bottom of a ship is made heavy, the center of gravity of the ship lies below the center of buoyancy and hence, the meta-center of the displaced liquid and the floating ship comes in stable condition even its equilibrium position is disturbed. So, this makes the stability of the ship.
3. If a cork is released from the bottom of a jar filled in water, what will happen and why?
The cork comes up when it is released from the bottom of a jar filled with water because of upthrust acting on it is greater than its weight and it floats in water.
4. When cork is floating in water, what is its apparent weight?
A body can float in water if the weight of body is equal to upthrust acting on it. The center of gravity of the body and the center of buoyancy of displaced water lie in the same line. Thus, cork becomes weightless.
5. Differentiate between density and specific gravity
The differences between density and specific gravity are:
|
Density |
Specific Gravity |
|
The quantity of matter per unit volume is called density of a substance. |
The ratio of density of any substance to the density of water at 4 degree Celsius is called specific gravity |
|
It is absolute value |
It is relative density |
|
Its unit is kg/m3 and gm/cm3 |
It is unitless quantity |
6. Why is it easier to lift a body in a liquid than in air?
The density of a liquid is greater than that of air. Since the upthrust depends on the density, the upthrust acting on the body is greater in water than in air and hence it is easier to lift the body in water.
7. In still air, a helium-filled balloon rises up to a certain height and then stops rising. Why?
The atmospheric pressure is greater near the surface and gradually decreases to the height. Since the density of helium gas is lower than that of air near the ground. The weight of the balloon will be smaller than the upthrust acting on it and the balloon rises to a certain height when upthrust is equal to its weight where the density of air and helium is same. After this height, the balloon stops to rise because the weight of the balloon becomes more than upthrust.
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