Upthrust
Contents
Key Stage 3
Meaning
Upthrust is a force that acts upwards in a fluid due to the fluid being displaced.
About Upthrust
- Upthrust is a force so it is measured in Newtons.
- The force of upthrust is equal to the weight of fluid that has been displaced by an object.
- An object in the water experiences more upthrust than an object in air because water is more dense than air.
- Upthrust is weak in the air because the air is not very dense. For most objects in air upthrust can be ignored because it is so small.
- Upthrust is caused by the pressure in a fluid. Pressure increases with depth so the bottom of an object will experience more pressure than the top. This difference in pressure results in a difference between the force on the bottom and the top, known as upthrust.
Examples
 |
 |
| A boat floats on the water because the weight is balanced by the upthrust. | A submarine can change the amount of upthrust in order to rise or sink in the water. |
Key Stage 4
Meaning
Upthrust is a force that acts upwards in a fluid due to the weight of the fluid being displaced.
About Upthrust
- Upthrust is a force so it is measured in Newtons.
- The force of upthrust is equal to the weight of fluid that has been displaced by an object.
- An object in the water experiences more upthrust than an object in air because water is more dense than air.
- Upthrust is weak in the air because the air is not very dense. For most objects in air upthrust can be ignored because it is so small.
- Upthrust is caused by the pressure in a fluid. Pressure increases with depth so the bottom of an object will experience more pressure than the top. This difference in pressure results in a difference between the force on the bottom and the top, known as upthrust.
- Upthrust = [(Pressure at base) - (Pressure at the top)] x (Area of top and bottom surface)
Examples
| |
|
| A boat floats on the water because the weight is balanced by the upthrust. | A submarine can change the amount of upthrust in order to rise or sink in the water. |
References
AQA
- Upthrust, page 137, GCSE Physics, Hodder, AQA
- Upthrust, page 173, GCSE Physics; Student Book, Collins, AQA
- Upthrust, page 59, GCSE Physics; The Revision Guide, CGP, AQA
- Upthrust, pages 168-169, GCSE Physics; Third Edition, Oxford University Press, AQA
- Upthrust, pages 172, 173, GCSE Physics; The Complete 9-1 Course for AQA, CGP, AQA
Edexcel
- Upthrust, page 102, GCSE Physics; The Revision Guide, CGP, Edexcel
- Upthrust, pages 204-205, GCSE Physics, Pearson Edexcel
- Upthrust, pages 321, 322, GCSE Physics, CGP, Edexcel