# Question about Elastic force and Buoyancy force

• MatinSAR
In summary,A wooden cube with a side of 10 cm is connected to the bottom of a water container by a spring. If the density of wood is 0.6g/cm^3 and the density of water is 1g/cm^3 , the elastic force of the spring is 4N.
MatinSAR
Homework Statement
Elastic force and Buoyancy force
Relevant Equations
Archimedes' principle
Suppose a wooden cube with a side of 10 cm is connected to the bottom of a water container by a spring. If the density of wood is 0.6g/cm^3 and the density of water is 1g/cm^3 , what is the elastic force of the spring? Is it 4N or 6N ?

I think the answer is 4N … But the book says it is 6N , Could you please guide me which one is correct ?!

My answer : Spring force = Buoyancy force - Weight of the cube = 10N - 6N = 4N

MatinSAR said:
My answer : Spring force = Buoyancy force - Weight of the cube = 10N - 6N = 4N
Your thinking looks good to me. (Did the book provide a solution or just the answer?)

MatinSAR
Doc Al said:
Your thinking looks good to me. (Did the book provide a solution or just the answer?)
It said the Spring force is equal to the Buoyancy force that acts on wooden cube and this Buoyancy force is equal to the weight of the cube due to complete submersion in water …

MatinSAR said:
... this Buoyancy force is equal to the weight of the cube due to complete submersion in water …
The weight of what cube?

MatinSAR
Lnewqban said:
The weight of what cube?
We have only one wooden cube in the question and the weight of the cube is 6N.

MatinSAR said:
It said the Spring force is equal to the Buoyancy force that acts on wooden cube
That's not right. (It ignores the weight of the cube.)
MatinSAR said:
and this Buoyancy force is equal to the weight of the cube due to complete submersion in water
That's also not quite right (as @Lnewqban points out).

What book are you using?

Lnewqban
MatinSAR said:
We have only one wooden cube in the question and the weight of the cube is 6N.
There was a heavier cube originally ocupying the volume of our unique and now submerged wooden cube.

Last edited:
MatinSAR
Doc Al said:
That's not right. (It ignores the weight of the cube.)
Thank you …
Doc Al said:
What book are you using?
It's not a reference book like Fundamentals of Physics or …
It was a kind of school book for being ready for the tests and exams …
Lnewqban said:
There was a cube originally ocupying the volume of our unique and now submerged wooden cube.
I'm sorry but I don't understand … Do you mean 6N is false ?!

MatinSAR said:
... I'm sorry but I don't understand … Do you mean 6N is false ?!
https://en.m.wikipedia.org/wiki/Buoyancy

The buoyancy effect is generated by the weight of the fluid that has been displaced by the volume of the fully submerged wooden cube.
The fluid surrounding the solid is puting pressure on it, trying to regain that volume.

Think of the cube as a piston of wood pushing down and a piston of water pushing up, only that harder, in the same ratio in which the densities of water and wood differ.

Last edited:
MatinSAR
Lnewqban said:
Thank you.

Lnewqban

## 1. What is elastic force?

Elastic force is the force that is exerted by a spring or other elastic material when it is stretched or compressed. It is a restorative force that tries to return the material to its original shape and size.

## 2. How is elastic force related to buoyancy force?

Elastic force is not directly related to buoyancy force. However, in some cases, elastic materials may be used to create buoyancy by displacing water or other fluids.

## 3. What is buoyancy force?

Buoyancy force is the upward force exerted by a fluid on an object that is partially or fully submerged in the fluid. It is equal to the weight of the fluid that is displaced by the object.

## 4. What factors affect the buoyancy force?

The buoyancy force is affected by the density of the fluid, the volume of the object, and the gravitational force acting on the object. It also depends on the shape and position of the object in the fluid.

## 5. How can we calculate the buoyancy force?

The buoyancy force can be calculated by multiplying the density of the fluid by the volume of the displaced fluid and the acceleration due to gravity. This can be represented by the formula Fb = ρVg, where Fb is the buoyancy force, ρ is the density of the fluid, V is the volume of the displaced fluid, and g is the acceleration due to gravity.

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