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A plastic cup containing air (literally empty) when immersed in water upside down it will tend to come up, likewise the piece of wood or bee wax will come up if totally or partially immersed in water

In both cases objects rise up due to upthrust force which is greater than the weight (mg) of objects. If the weight would be greater than the upthrust then the object would sink but would be much lighter if measured when immersed in water.

Upthrust force is also known as buoyant force

Buoyant force is an upward force exerted by a fluid to a body which is partially or totally immersed in it and it is equal in magnitude to the weight of fluid displaced by a body.

ARCHIMEDES' PRINCIPLE (LAW OF BUOYANCY)

States that, when a body is partially or totally immersed in fluid, it experiences an upthrust force which is equal to the weight of fluid displaced.

Experiment to show upthrust is equal to the weight of the fluid displaced

A is a real weight (weight of an object in air) 4.5 N

B is apparent weight (weight of an object in fluid) 3.0 N

C is apparent loss of weight (weight of fluid displaced) 1.5 N

Measuring the weight of displaced fluid is equal to apparent loss of weight; this apparent loss is the buoyancy force on an object which is upthrust.

Apparent loss of weight is equal to the weight of displaced fluid.

Real weight = apparent weight + apparent loss

Since apparent loss is equal to upthrust

Real weight = apparent weight + upthrust

Upthrust =real weight - apparent weight.

A body weighs 5.5 N when measured in air and 3 N when completely immersed in kerosene, what is upthrust experienced by a body.

Weight of body in air (Real weight) =5.5 N

Apparent weight of a body when immersed in kerosene = 3 N.

But upthrust = real weight - apparent weight loss

A body weighs 3 N when totally immersed in water contained in an overflow can, if weight of displaced water was 2.6 N, what is the real weight of an object.

Upthrust = 2.6 N (according to Archimedes' principle)

Upthrust = real weight - apparent weight

2.6 N = Real weight - 3 N.

Real weight = 2.6 N + 3 N

If mass is multiplied by gravitational acceleration 'g' becomes weight (times 10 above and below which does not change magnitude but changes the physical quantity from mass to weight)

Weight of a given volume of substance: - is the weight of substance in air.

Weight of an equal volume of water: - is the weight of water displaced (liquid has to be water because the density of solid object is compared to the density of water, meaning of relative density)

A metal block weighs 108 g in air and 68 g in water, find the relative density of metal. What possibly this metal can be? (Use the table of densities).

A body weighs 135 g in air displaced 54 g of water when completely immersed, find the relative density and volume of a body.

Volume of a body is equal to the volume of displaced water.

Therefore 1 g/cm ³= 54 g/volume

DETERMINATION OF RELATIVE DENSITY OF OBJECT THAT FLOATS BY ARCHIMEDES' PRINCIPLE

AIM: To determine the relative density of an object that floats by Archimedes' principle.

REQUIREMENTS: floating object, sinker (piece of metal or stone), spring balance, string, and water in a beaker

In an Experiment to find the relative density of floating object the followings were observed,

If an object of given volume is totally immersed in different liquids it will always displace volume of given liquid equals to its own volume but the masses of these equal volumes of liquids displaced will differ owing to their densities(concentration of particles)

We can simply know mass of liquid displaced by noticing the apparent loss of mass of an object when totally immersed in liquid; this is according to Archimedes' principle.

Remember, when mass is multiplied by 'g' (gravitational acceleration) it becomes weight also:-

AIM: TO FIND RELATIVE DENSITY OF 'X'

REQUIREMENTS: Liquid x in a beaker, water in a beaker, object that can sink, and spring balance.

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A plastic cup containing air (literally empty) when immersed in water upside down it will tend to come up, likewise the piece of wood or bee wax will come up if totally or partially immersed in water In both cases objects rise up due to upthrust force which is greater than the weight (mg) of objects.

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point where total upthrust due to fluid displaced by the immersed part of the body

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Suppose an object ABCD of base area A. Whose side AB is at depth h ₁ and side CD is at
depth h ₂. If density of water is 'd' and gravitaitonal acceleration 'g', then
pressure on surface AB is P ₁ = h ₁ d g.
Force on surface AB is F ₁= A P ₁ = A h ₁ d g
Pressure on surface CD is P ₂ = h ₂ d g.
Force on surface CD is F ₂=A P ₂ = A h ₂ d g
Resultant force on object is F = F ₂ - F ₁

or Upthrust = A h ₂ d g - A h ₁ d g

= A d g ( h ₂ - h ₁)

= V d g

= mg

∴ Upthrust = weight of object

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Points to be noted

1. → Density of iceberg is less than the water so iceberg floats in water.

2. → Density of dead body is less than water but head is more denser so a dead body floats with its head immersing in water.

3. → Egg density is more than water so it sink in pure water but Egg has less density than salty water so it floats on salty water.

4. → Having higher density salty water give more upthrust than pure river water so it is easire for a man to swim in sea water than in river water.

5. → Water give upthrust on stone when put in it so it is easier to lift a heavy stone inside the water.

6. → Density of iron nail has high than water but have low density than mercury so iron nail sink in water and floats in mercury

7. → Iron has high density than water. Iron nail couldn't displace water at least equal to its weight but ship of wider base can displace water equal to its weight so nail sinks and ship floats.

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1. All liquids exert an upthrust on an object immersed in them.

2. Upthrust increased with increase in volume of the object.

3. Uothrust increases with density of fluid.

4. There is a loss of weight when immersed in a liquid.

5. Even air exerts an upthrust

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The upward force experienced by a body when partly or wholly immersed in a fluid is called upthrust or buoyant force. Phenomenon responsible for the same is called buoyancy.

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Q Why is water at 4 degree celsius used for comparison

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Q Why is water at 4 degree celsius used for comparison

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Ans Water attains maximum density at 4 degree celsius

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Determination of Relative Density of Solid

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A video explaining the determination of relative density of solid for 8th class (grade) CBSE science students in India. For many more such videos and complete customized solutions to schools and students on a wide range of devices, please contact sales@edewcate.com EzyLearn Digiclass is the most advanced digital curriculum software in the country that enables teachers and students to communicate and derive maximum benefit out of the vast digital resources made avaialable to them at the lowest price in the market.

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ExploreLearning : Get hands-on, minds-on in math and science

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Archimedes' Principle Gizmo : ExploreLearning

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Place weights into a boat and see how far the boat sinks into a tank of liquid. The depth of the boat can be measured, as well as the amount of liquid displaced. The dimensions of the boat and the density of the liquid can be adjusted.

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BUOYANCY | ARCHIMEDES PRINCIPLE - Interactive flash animation to understand how the water acts upon immersed objects. Interactive Physics Simulations | Interactive Physics Animations | Physics and Chemistry by a Clear Learning in High School, Middle School, Upper School, Secondary School and Academy. PCCL | jean pierre fournat

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BUOYANCY | ARCHIMEDES PRINCIPLE - Interactive free flash animation to understand how the water acts upon immersed objects. Interactive Physics Simulations | Interactive Physics Animations | Physics and Chemistry by a Clear Learning in High School, Middle School, Upper School, Secondary School and Academy. PCCL | jean pierre fournat

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In this TedEd, the Archimedes principle will be explored using a pre-existing video found on YouTube to guide our learning.

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Buoyancy - Can you drown in the dead sea? | #aumsum #kids #science #education #children

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When will objects float and when will they sink? Learn how buoyancy works with blocks. Arrows show the applied forces, and you can modify the properties of the blocks and the fluid.