Upthrust and Floating
Upthrust is the upward force a fluid exerts on an object in it, equal to the weight of the fluid displaced.
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Upthrust is the upward force a fluid exerts on an object in it, equal to the weight of the fluid displaced.
- An object floats when upthrust equals its weight
- Ships float by displacing a lot of water
- Denser fluids give more upthrust
🧠 Quick quiz
Three questions. Score 2 or more to complete the topic.
What is Upthrust and Floating?
Within Physics, which covers forces, energy, waves, electricity, magnetism, light and space explained through motion and experiments, this topic explains Upthrust and Floating. Physics topics explain how things move, push, heat up and carry energy, so each one here pairs a definition with a live model you can change.
Check that you can explain Upthrust and Floating in your own words and give one example from everyday life. If you can do that, you have understood the core idea.
Understanding Upthrust and Floating explains how the physical world behaves, from sport and transport to electricity and medicine.
Upthrust and Floating in detail
Upthrust is the upward force exerted by a fluid on an object that is partly or wholly submerged. It occurs because pressure increases with depth, so the push on the bottom is greater than the push on the top. By Archimedes' principle, the upthrust equals the weight of fluid displaced.
An object floats when its weight equals the upthrust, which happens when its average density is less than the fluid's. Ships float because their hollow shape displaces a large volume of water, and submarines control buoyancy by changing the amount of water in their tanks. Hot-air balloons use the same ideas in air.
How the interactive helps you understand Upthrust and Floating
Watch the force arrows in the interactive. Use any sliders or buttons it offers to change the values and see how the force arrows responds.
Before you change anything, predict the result. Then change one value at a time and check whether your prediction was right. This is a quick way to build a correct mental model of Upthrust and Floating.
Real-life uses and examples
- Use Upthrust and Floating to make sense of a practical and its results.
- Answer “explain” questions by linking Upthrust and Floating to a clear cause and effect.
- Predict what a ball, car or circuit will do with Upthrust and Floating before you do the calculation.
Common mistakes to avoid
- Mixing up Upthrust and Floating with a related quantity that has different units.
- Forgetting that some quantities, such as force or velocity, also have a direction.
- Learning the definition without testing it. Use the quiz and the interactive to check that you can apply the idea.
Frequently asked questions about Upthrust and Floating
What is Upthrust and Floating?
Upthrust is the upward force a fluid exerts on an object in it, equal to the weight of the fluid displaced.
What are the most important points about Upthrust and Floating?
The main points are: An object floats when upthrust equals its weight; Ships float by displacing a lot of water; Denser fluids give more upthrust.
Why is Upthrust and Floating useful?
Understanding Upthrust and Floating explains how the physical world behaves, from sport and transport to electricity and medicine.
How can I practise Upthrust and Floating?
Open the interactive at the top of this page and change the controls one at a time. Predict the result before each change, then take the three-question quiz. A score of two or more marks the topic as complete on this device.
Which topics are related to Upthrust and Floating?
Related topics in Physics include Gravitational Potential Energy, Power, Momentum.