Origin of Upthrust: Displaced Water & Pressure Difference

In summary: So when an object is submerged in a fluid, the pressure increases with depth and this results in a difference in pressure between the top and bottom surfaces. This difference in pressure creates a resultant force that acts upwards, known as the upthrust or buoyant force. The origin of this upthrust is the weight of the displaced fluid, as described by Archimedes' principle. In summary, when an object is submerged in a fluid, the difference in pressure between the top and bottom surfaces creates an upward force known as upthrust, which is caused by the weight of the displaced fluid.
  • #1
Janiceleong26
276
4

Homework Statement


When an object is submerged or floats in a fluid, the..
Pressure on bottom surface > Pressure on top surface
So the resultant force is acting upwards.

Why the difference in pressure? Must both, the top and bottom surfaces, have the same area of contact with the fluid? Since P=F/A ?

A sealed cylindrical steel can is submerged in water. What is the origin of upthrust that acts on the can?
The weight of displaced water acts upwards on the can.
^ This statement does not states the origin of upthrust...Why? It seems right ! Feeling confused
2. Relevant equation
P=F/A
P=hρg
 
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  • #2
Janiceleong26 said:
Why the difference in pressure?
Pressure depends on depth below the surface--the deeper you go, the greater the pressure.

As expressed by this equation (h is the distance below the surface):
Janiceleong26 said:
P=hρg
 
  • #3
Doc Al said:
Pressure depends on depth below the surface--the deeper you go, the greater the pressure.

As expressed by this equation (h is the distance below the surface):
But upthrust is a force, whereas pressure isn't ..
 
  • #4
Janiceleong26 said:
But upthrust is a force, whereas pressure isn't ..
Yes, but a pressure applied over an area results in creation of a force, F = P * A.

What you seem to be missing is information about Pascal's Law, which Doc Al provided in mathematical form in Post #2, and also Archimedes' principle and the concept of buoyancy, which is another name for this upthrust.

05-lecture-outline-26-638.jpg
 
  • #5
Janiceleong26 said:
But upthrust is a force, whereas pressure isn't ..
But you use pressure (and area) to calculate the force, as you stated yourself in your first post.
 
  • #6
Doc Al said:
But you use pressure (and area) to calculate the force, as you stated yourself in your first post.
I see, thanks ! Got it
SteamKing said:
Yes, but a pressure applied over an area results in creation of a force, F = P * A.

What you seem to be missing is information about Pascal's Law, which Doc Al provided in mathematical form in Post #2, and also Archimedes' principle and the concept of buoyancy, which is another name for this upthrust.

05-lecture-outline-26-638.jpg
Thanks! I got it now
 

FAQ: Origin of Upthrust: Displaced Water & Pressure Difference

What is upthrust?

Upthrust is a force that pushes objects upwards in a fluid, such as water. It is also known as buoyancy force.

How is upthrust related to displaced water?

Upthrust is caused by the displacement of water by an object. When an object is immersed in water, it pushes aside water molecules, creating a pressure difference that results in an upward force.

What is the role of pressure difference in upthrust?

Pressure difference is a crucial factor in determining the magnitude of upthrust. The greater the pressure difference between the top and bottom of an object in water, the greater the upthrust force.

How does the shape and size of an object affect upthrust?

The shape and size of an object play a significant role in determining the amount of upthrust it experiences. Objects with a larger surface area will experience more upthrust due to the larger pressure difference created.

Can upthrust be greater than the weight of an object?

Yes, upthrust can be greater than the weight of an object. This is known as positive buoyancy and is what allows objects to float in water. When the upthrust force is greater than the weight of an object, it will rise to the surface of the water.

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