This document discusses upthrust, Archimedes' principle, and floatation. It defines upthrust as the upward force exerted on a body submerged in a fluid. According to Archimedes' principle, the upthrust on a body is equal to the weight of the fluid it displaces. The principle of floatation states that an object floats when the upthrust equals its weight, and sinks when the upthrust is less than its weight. Applications of these principles include why ships and nails float or sink, and the purpose of the Plimsoll line marked on ship hulls.

1. Upthrust in fluids,
Archimedes principle
and Floatation.
By: Alfiya Pathan

2. • https://www.youtube.com/watch?v=3PGNTZ4RbuM

3. • Buoyancy and Upthrust:
• The upward force exerted on a body by the fluid in which it is
submerged, is called as Upthrust or buoyant force.
• Upthrust being a force is measured in N or Kgf.

6. Pushing a cork into water.

7. • NOTE
• Like liquids, gases also have property of buoyancy. i.e. a body
immersed into gas also experience Upthrust.
• It is negligibly small as compared to our body weight.
• A balloon filled with hydrogen gas rises up because of buoyancy on
balloon due to surrounding air.

8. • Condition of a body to float or sink in
a fluid:
i. Buoyant force is greater than mass =
float completely
ii. Buoyant force equal to mass = float
partly
iii. Buoyant force less than mass = sink

9. • Characteristic properties of
Upthrust:
• Larger the volume of body submerged in a fluid, greater is the
Upthrust.

10. • For same volume inside the fluid more the density of fluid, greater is
the Upthrust.
• The Upthrust acts on the body in upward direction at the center of
buoyancy.

11. • Reason for Upthrust:
• If an object is immersed in the
liquid, liquid applies pressure on
that object in all directions..
• The pressure increases with the
depth.
• force = pressure x area
• Thus, difference in pressure due
to liquid on the two faces of
then block causes a net upward
force.

12. • Upthrust is equal to the weight of
displaced liquid:
• When a body is immersed in a liquid,
Upthrust on it due to liquid is equal to
the weight of the liquid displaced by the
submerged part of the body.

13. • Archimedes principle:
• When a body is partially or completely immersed in a liquid, it
experiences an Upthrust, which is equal to the weight of the liquid
displaced by it.
• Solid bodies with densities greater than density of liquid sink, while
solid bodies with density less than density of liquid floats.

14. •FLOATATION:

15. • Principle of floatation:
• When a body is submerged in the liquid the following two forces acts
on it.
• 1. The weight of the body acting vertically downwards.
• 2. The Upthrust of the liquid acting vertically upwards.
• In magnitude,
• W = volume of body x density of body x g
• F = Volume of submerged part of the body x density of liquid x g

18. • Weight of the body = Weight of the liquid displaced by the submerged
part of the body.
• W = F (buoyant force)
• Therefore, apparent weight of a floating body = 0
• This is called as principle of floatation.
• The weight of a floating body is equal to the weight of the liquid
displaced by the submerged part.

19. • Relation between volume of
submerged part of the body, the
densities of liquid and the body.

20. • Applications of the principle of
floatation:
• An iron nail sinks in water while a ship floats.
• A loaded ship submerged more while an unloaded ship is less
submerged.
• A ship begins to submerge more as it sails from sea water to river
water.
• An unloaded ship is filled with sand at its bottom.
• It is easier for a man to swim in sea water than in fresh water.

21. • Plimsoll line:
• The Plimsoll line is a reference mark
located on a ship’s hull that indicates
the maximum depth to which the
vessel may be safely immersed when
loaded with cargo. This depth varies
with a ship’s dimensions, type of
cargo, time of year, and the water
densities encountered in port and at
sea. Once these factors have been
accounted for, a ship’s captain can
determine the appropriate Plimsoll
line needed for the voyage