Upthrust
Every liquid has a tendency to push the object towards its surface called upthrust. When a stone is immersed in water, water tries to push the stone to its surface. During this process the stone will lose some of its weight because water is trying to push it upward. Similarly water also pushes your body upward when you throw yourself into swimming pool. So it is easier for you to swim. So the upthrust of water will be
Upthrust = weight in air  weight in water.
Density and relative density:
Density is a physical property of a matter. It can be defined as a ratio of mass per unit volume. The qualitative definition can be the measure of the relative heaviness of an object with constant volume. For example, rock is denser than a piece of paper though they occupy the same volume (differ in the quantity of mass occupied in the same volume).
Formula for measuring density is density= \(\frac{mass}{volume}\). Unit of density is kg/m^{3}
Relative density is the ratio of the density of the substance to the density of water at 4 degree Celsius. Relative density does not have aunit. According to the density of the liquid, upthrust differs. If the liquid has higher density then upthrust exerted by it increases. That is why an egg does not float on pure water but floats on salt water. With the addition of salt,we increase the density of water. Due to higher density,the egg floats.
 Every liquid has a tendency to push the object towards its surface called upthrust.
 Formula for measuring density is : density= \(\frac{mass}{volume}\). The unit of density is kg/m^{3} .
 The ratio of the density of the substance to the density of water at 4 degree Celsius with the same volume is called relative density.
Solution,
Weight of body in liquid= 10N
Weight of displaced liquid= 2N
Weight of body in air=?
Using formula,
Weight of body in air= weight of body in liquid+ weight of displaced liquid
= 10+2
=12N
Upthrust= Weight of displaced liquid
= 2N
For mass of body,
Weight of body in air(W)=12N
Acceleration due to gravity= 10m/s^{2}
Mass of the body (m)=?
Using formula,
\begin{align*}m &=\frac{W}{g}\\ &= \frac{12}{10}\\&=1.2 \: kg. \end{align*}
Here,
Weight of stone in water= 9N
Weight of displaced water= 2N
Weight of stone in air=?
We know,
The weight of stone in air= Wt. of stone in water+ Wt. of displaced water
=9N +2N
=11N
Solution,
Upthrust of water=Weight of displaced water
=10N
Now,
Weight of stone in water=40N
Weight of displaced water =10N
Weight of stone in air=Wt. of stone in air+ Wt. of displaced water
=40N + 10N
= 50N
Here,
The weight of iron in air= 20N
The weight of iron in water= 12N
The weight of water displace by iron= ?
we know,
The weight of water displaced by iron=wt of iron in air wt of iron in water
=20N12N
=8N
The upthrust on the iron= weight of displaced water = 8N
Upthrust = Wt. of displaced water
∴8N=8N
Here,
Wt. of stone in water= 3N
Wt. of displaced water= 5N
we know that,
The wt. of stone in air= Wt. of stone in water+wt. of displaced water
=3N+ 5N
=8N
Again,
Upthrust= Weight in air Weight in water
=8N3N
=5N
Hence, upthrust of water is 5N and the weight of stone in air is 8N.
Here,
Weight of the object in air (W_{a}) =34N
Weight of the object in water (W_{w}) =10N
Upthrust = ?
Weight of the water displaced (W_{2}) =?
We know that,
Upthrust = W_{a}W_{w}
= 3410
= 24N
Again,
We know,
Upthrust (U) = Weight of the liquid displaced(W_{2})
∴ the weight of the liquid displaced =24N
Thus, upthrust on the body is 24N and weight of displaced fluid is 24N.

Liquid pressure depends on ______.
magnetic force
gravitational force
frictional force
acceleration due to gravity

Objects tend to lose weight when immersed in liquid due to ______.
upthrust
mass
gravity
pressure

Which one is true?
Upthrust =weight in water weight in air
all of these
Upthrust = weight in air  weight in water
Upthrust = weight in air + weight in water

The formula for measuring density is density ______.
massvolume
mass x volume
mass/volume
mass+volume

Relative density is the ratio of the density of the substance to the density of water at ______.
4^{0}C
44^{0}C
40^{0}C
5^{0}C

Relative density does not have ______.
mass
unit
volume
gravity

You scored /6
Any Questions on Upthrust ?
Please Wait...
Discussions about this note
Forum  Time  Replies  Report 

shrehow to prove upthrust =vdg 
Jan 16, 2017 
0 Replies View Replies 

SarojHydrolic press is called an instrument for multiplication of forces why 
Jan 06, 2017 
1 Replies View Replies 

please reply me fast 
Jan 02, 2017 
0 Replies View Replies 

iron do no float why???? 
Jan 02, 2017 
1 Replies View Replies 