Viva Voce: Archimedes’ Principle | Extra Documents & Tests for Class 9 PDF Download

Q.1. Why do you feel light while swimming?

While swimming, water (fluid), exerts an upward force on the body this is called upthrust or buoyant force, because of this buoyant force we feel light

Q.2. Why does the plastic bottle float on water?

When the upward force acting on the bottle is more than the downward force acting on the bottle then it will float.

Q.3. A cork and iron nail have same weight. When immersed in water nail sinks but cork floats. Why?

This is because the density of cork is less than iron nail, it is also less than water density. Hence the upward force exerted by water on cork is much greater than the density of the cork, so it floats on water.

Q.4. State Archimedes’ principle.

When a body is immersed fully or partially in a fluid, it experiences an upward force that is equal to the weight of the fluid displaced by it.

Q.5. Name the device used to determine the density/purity of a sample of milk.

Lactometer

Q.6. What is the unit of relative density?

It has no unit, as it is a ratio of similar quantities.

Q.7. What is relative density?

The relative density of a substance is the ratio of its density to that of water.

Relative density = Density of a substance / Density of water

Q.8. Name the device used to determine the density of liquids.

The density of liquids can be determined by hydrometer, it is based on Archimedes’ principle.

Q.9. A boy swims in river water and in sea water. In which case he finds swimming easier?

It is easy to swim in sea water as it is denser and exerts more upthrust/buoyant force and makes floating easier.

Q.10. What is the downward force acting on the bottle immersed in water?

The downward force is due to the gravitational attraction of the earth.

Q.11. On what factor does the magnitude of the upward force depend?

The magnitude of the buoyant force depends on the density of the fluid.

Q.12. What are fluids?

Anything that flows is called a fluid. All liquids and gases are fluids.

Q.13. In what direction does the buoyant force on an object immersed in a liquid act?

The buoyant force acts in an upward direction.

Q.14. Why can’t we call solids as fluids?

Solids cannot flow, so they are not fluids.

Q.15. Can fluids exert pressure?

Yes, fluids exert pressure in all directions.