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upthrust

Primary Information
Secondary Information

Definition

Upthrust, also known as buoyancy, is the force exerted by a fluid that opposes the weight of a partially or fully immersed object. The upthrust is equal to the weight of the fluid displaced by the object.

Upthrust is caused by the difference in pressure between the top and bottom of the object. The pressure on the top of the object is lower than the pressure on the bottom. This is because the weight of the fluid pushes down on the bottom of the object.

The upthrust is calculated by the following formula:

  • Upthrust = Volume of fluid displaced × Density of fluid × Gravitational acceleration
  • The volume of fluid displaced is the volume of the object that is submerged in the fluid. The density of the fluid is the mass of the fluid per unit volume. The gravitational acceleration is the acceleration due to gravity, which is approximately 9.8 m/s² on Earth.
  • Upthrust is what keeps boats afloat. The weight of the water displaced by the boat is equal to the weight of the boat, so the boat does not sink.

Upthrust is also what allows submarines to float or sink. By adjusting the amount of water that is displaced, submarines can change their buoyancy and thus their depth in the water.

How can the word be used?

The upthrust of the ground caused the foundation of the building to crack.

upthrust

Different forms of the word

Noun:

  • upthrust (a force that pushes something upward).
  • uplift (a geological term for an upthrust).
  • heave (a sudden upward movement).

Adjective:

  • upthrust (moving or pushing upward).
  • uplifting (giving hope or encouragement).

Etymology

The word "upthrust" comes from the Old English words "up" and "thrust", which mean "up" and "push" respectively. The word "upthrust" is first attested in English in the 16th century.

Question

What is an upthrust force?

AQA Science Exam Question and Answer

Question:

Explain the concept of upthrust in the context of fluid mechanics. Describe how upthrust, also known as buoyant force, operates and its relationship with an object's weight and volume. Provide an example of a real-world scenario where upthrust plays a significant role.

Answer:

Upthrust, also referred to as buoyant force, is a fundamental principle in fluid mechanics that explains the apparent loss of weight experienced by an object immersed in a fluid, such as a liquid or gas. It is a result of the pressure difference between the upper and lower surfaces of the object when submerged.

When an object is placed in a fluid, the fluid exerts pressure on all its surfaces. The pressure at the lower surface is higher than at the upper surface due to the increasing depth of the fluid. This pressure difference creates an upward force on the object, known as upthrust or buoyant force. This force opposes the object's weight and causes it to feel lighter than it does in air or a vacuum.

The magnitude of upthrust is proportional to the volume of fluid displaced by the object and the density of the fluid. Archimedes' principle states that the upthrust is equal to the weight of the fluid displaced by the object. This relationship between weight, volume, and density governs the behaviour of floating and sinking objects.

A classic example of upthrust in action is when a ship floats on water. The ship's massive structure displaces a volume of water equal to its weight, resulting in an upward buoyant force that supports the ship's weight. This principle enables ships, boats, and other floating vessels to stay afloat despite their considerable mass.