Wednesday, October 16, 2013


1. Pressure : The thrust (force) acting normally on unit area of a surface is called pressure.
2. SI unit of pressure is newton/(metre)2 or N/m2. It is commonly called pascal (Pa).
3. Definition of Pascal : When a force of 1 newton acts normally on an area of cross-section
1m2, then the pressure experienced by the surface is said to one pascal.
4. Buoyancy : The phenomenon due to which a body on being immersed in a fluid experiences
an upward force is called buoyancy.
5. Buoyant force or upthrust : The upward force experienced by a body on being immersed
in a fluid is called buoyant force or upthrust.
6. Buoyant force or upthrust acting on a body is always equal to the weight of the fluid displaced
by the immersed part of the body in the fluid.
7. Archimedes’ Principle : When a body is partially or wholly immersed in a fluid, it
experiences an upthrust (or apparently loses its weight) which is equal to the weight of the
fluid displaced by the immersed part of the body.
8. Density : Mass per unit volume of a substance is called density. Its unit in CGS system is
g/cm3 and in SI system is kg/m3.
9. Relative density : The ratio between the density of a substance and the density of water at
4°C called relative density.
The relative density is a pure number and has no units.

  1. Give reason why, a block of plastic when released under water comes up to the surface of Water
  2.  Why does a mug full of water feel lighter inside water?
  3.  State Archimedes’ principle
  4. When we stand on loose sand, our feet go deep into the sand. But when we lie down on the sand our body does not go that deep in the sand. Why?
  5.  A cork floats in water, while the iron nail sinks. Give reason
  6. State Archimedes’ Principle. Based on this principle, write its two applications
  7.  If two equal weights of unequal volumes are balanced in air, what will happen when these are completely dipped in water?
  8. The volume of 40 g of a solid is 15 cm3. If the density of water is 1 g/cm3 , will the solid float or sink? Why?
  9. (a)  Explain why a truck or a motor bus has much wider tyres?(b)  Why do we feel lighter when we swim?
  10. What happens when :
  11. (a)  Buoyant force exerted by the fluid is less than the weight of the body?(b)  Buoyant force exerted by the fluid is equal to the weight of the body?
  12. Cutting tools have sharp edges?
  13. A sheet of paper falls slower than one that is crumpled into a ball?

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