

The S.I. unit of buoyant force is
Newton.
This upward force that acts on an object
when immersed in a fluid is called buoyant force.
Two main factors on which the buoyant
force depends are: (i) Density of the fluid. (ii) Value of acceleration
due to gravity at that place.
When an iron nail is placed on the
surface of water it sinks whereas ship made up of iron floats. This is because
size or volume of the ship is more.
If the density of the liquid is
more than the density of the material of the body then the body floats due to
the buoyant force exerted by it and viceversa.
Density of a substance is the mass of
the substance contained in a unit volume of that substance.
Density of an object is given as
Mass/Volume
Buoyant force experienced by a body when
submerged in a liquid depends on the volume of the body and the density of the
liquid.
The density of a substance is one of its
characteristic properties and used to determine the purity of any substance.
Floating and Sinking depends
on density of water and the density of an object
If the density of an object is less than
the density of water it floats. This means that the up thrust of water on an
object is greater than the weight of the object.
If the density of an object is more than
the density of water it sinks. This means that the up thrust of water on an
object is less than the weight of the object.
Therefore objects of density less than
that of a liquid float on the liquid. The objects of density greater than that
of a liquid sink in the liquid.
Two forces act on an object immersed in
water. One is the gravitational force, which pulls the object downwards, and
the other is the buoyant force, which pushes the object upwards.
If the upward buoyant force is greater
than the downward gravitational force, then the object comes up to the surface
of the water
The density of the substance is more
than the density of water ( 1 g/ cm3) than it will sink in water.
Relative density of a substance is the
ratio of density of substance to the density of water. It is also called
specific gravity.
Relative density = Density of
substance/density of water
Relative density of a substance help us
determine the purity of a substance by measuring its relative density
Examples: We use lactometer to differentiate between pure and
impure(measure the impurity) milk. We can measure the impurity of water using
hydrometer.
What is meant by the statement relative
density of gold is 19.3?
It means that gold is 19.3 times denser
than an equal volume of water. Those objects whose relative density is less
than one will float in water and those greater than one will sink.
5 kg of cotton occupies more space than
5 kg of iron. The particles of iron are closely packed while that of cotton are
loosely packed. The amount of iron packed in a unit volume is more. This
explains as to why iron is heavier than the same volume of cotton.
In Physics, word density help us
to describe the lightness or heaviness of different substances
Why is it difficult to hold a school bag
having a strap made of a thin and strong string?
It is difficult to hold a school bag having a strap made of a thin and strong string because it apply the large pressure on the shoulders due to very small contact surface area . we know that the pressure is inversely proportional to the surface area on which the force acts
Why is it difficult to hold a school bag
having a strap made of a thin and strong string?
It is difficult to hold a school bag
having a strap made of a thin and strong string because it
apply the large pressure on the shoulders due to very small contact
surface area . we know that the pressure is inversely proportional to the
surface area on which the force acts
What do you mean by buoyancy?
The tendency of a liquid to exert an
upward force on an object placed in it is called buoyancy.
When a body is completely or partially immersed in a fluid, then the upward thrust acting on the body is called force of buoyancy or buoyant force.
When a body is completely or partially immersed in a fluid, then the upward thrust acting on the body is called force of buoyancy or buoyant force.
It increases as we push the object
deeper into water. The magnitude of this buoyant force depends on the density of
the fluid.
Why does an object float or sink when placed on the surface of
water?
An object floats or sinks when placed on the surface of
water because of the buoyant force acting on the object.
If the density of
an object is less than the density of water it floats. This means that the up thrust of
water on an object is greater than the weight of the object.
If the density of
an object is more than the density of water it sinks. This means that the up thrust of
water on an object is less than the weight of the object.
Therefore objects
of density less than that of a liquid float on the liquid. The objects of
density greater than that of a liquid sink in the liquid.
Why the cutting edge of a knife should be as sharp as
possible?
The cutting edge of a knife should as sharp to create greater
pressure even for a very small applied force for quick action.
When we
weight our body, a downward ward gravitational force acts on it. Hence our actual mass is less than 42 kg
You have a bag of cotton and an iron bar, each indicating a mass of 100 kg when measured on a weighing machine. In reality, one is heavier than other. Can you say which one is heavier and why?
You have a bag of cotton and an iron bar, each indicating a mass of 100 kg when measured on a weighing machine. In reality, one is heavier than other. Can you say which one is heavier and why?
In reality, a bag of an iron bar is
heavier than a bag of cotton.Each indicating a mass of 100 kg when measured on
a weighing machine as more gravitational force act on a bag of cotton due to
its larger the surface area.
In what direction does the buoyant force on an object immersed in a
liquid act?
Ans: The buoyant
force acts on an object in the vertically upward direction through the center
of gravity of the displaced liquid.
Why does a block of plastic released under water come up to the
surface of water?
A block of plastic released under
water come up to the surface of water because the up thrust or the buoyant
force exerted by the water is greater than the downward gravitational
force.
The volume of 50 gm of a substance is 20 cm^{3}. If the
density of water is 1 g/cm^{3}, will the substance float or sink?
Given the mass of
the substance = 50 g Volume of the substance = 20 cm^{3}
Density of
substance = Mass /Volume = (50 /20) g/cm^{3} = 2.5 g/cm^{3}
Since the density
of the substance 2.5 g/cm^{3 }is greater than the density of water (1 g/cm^{3}), so the substance will sink in the water.
The volume of a 50 gm sealed packet is 350 cm^{3}. Will the
packet float or sink in water if the density of water is 1 g/cm^{3} ?
What will be the mass of the water displaced by this packet ?
Mass of packet =
500
g
Volume of packet = 350 cm^{3}
Density of packet =
Mass ÷ Volume = (500 / 350) g/cm^{3} = 1.43 g/cm^{3}
The sealed packet
will sink in the water as its density 1.43 g/cm^{3 }is more than that of water.
The volume of water
that will be displaced by the packet = 350 cm^{3}
And mass of this displaced water = Volume x Density = 350
x 1 = 350 gm.
State Archimedes’ principle. Give any two applications of Archimedes principle?
State Archimedes’ principle. Give any two applications of Archimedes principle?
Archimedes’ principle states that when a body is immersed
partially or fully in a fluid, it experiences an upward force that is equal to
the weight of the fluid displaced by it.
The two applications of Archimedes principle are given
below:
(i) Floating of ships and submarines (ii) The lactometers to test purity of milk
(i) Floating of ships and submarines (ii) The lactometers to test purity of milk
How do a submarine sink and float on water?
A submarine can both sink and float
on water because of the ballast tank .
To make a submarine sink into the water, these tanks are
filled with water. This increases the weight of the submarine and it
sinks.
To make a submarine float on the water surface, these tanks are emptied by pumping out water from them. This decreases the weight of the submarine and it floats
To make a submarine float on the water surface, these tanks are emptied by pumping out water from them. This decreases the weight of the submarine and it floats