Centre of Mass
Contents
Key Stage 4
It was essential to find the centre of mass of old steam trains to make sure it was low enough that it wouldn't tip over on the tracks at a turn. To do so they hung the entire engine from the ceiling from different points and drew chalk lines directly down from those points. There are two points of intersection where the centre of mass was found. One when the boiler was empty and one when it was full.
Meaning
The centre of mass is the average position all the matter in an object.
About Centre of Mass
- The centre of mass is also sometimes called the centre of gravity which is the point in an object where weight seems to act from.
- When calculating forces and drawing free body diagrams objects can be modelled as if they were a sphere at the centre of mass.
- The centre of mass of a lamina object can be found by hanging it from a point. The centre of mass will be directly below the point from which it is hung. Hanging it from a second point the centre of mass will also be below this new point. Those lines will cross over at the centre of mass.
Method to find the Centre of Mass of a Lamina
- Hang the lamina from a point.
- Hang a plumb line from that point.
- Draw a line down the lamina following the string of the plumb line.
- Hang the lamina from a second point.
- Repeat steps 2 and 3.
The point where the lines cross will be the centre of mass.
A third line can be drawn to confirm this location.
Extra Information
References
AQA
- Centre of mass, pages 157, 169, GCSE Physics; Student Book, Collins, AQA
- Centre of mass, page 120, GCSE Physics, Hodder, AQA
- Centre of mass, page 129, GCSE Combined Science Trilogy; Physics, CGP, AQA
- Centre of mass, page 149, GCSE Physics; The Complete 9-1 Course for AQA, CGP, AQA
- Centre of mass, page 204, GCSE Combined Science; The Revision Guide, CGP, AQA
- Centre of mass, page 52, GCSE Physics; The Revision Guide, CGP, AQA
- Centre of mass, pages 124-125, GCSE Physics; Third Edition, Oxford University Press, AQA
- Centre of mass, pages 210, GCSE Combined Science Trilogy 2, Hodder, AQA
Key Stage 5
Meaning
The centre of mass of a body is the point through which a single force on the body has no turning effect.
About the Centre of Mass
- The centre of mass is the average position of all the mass in an object.
- For a symmetrical object with uniform density, the centre of mass is at its geometric centre.
- The location of the centre of mass affects the stability of an object.
- In irregularly shaped objects, the centre of mass may not coincide with the geometric centre.
- The centre of mass can be outside the physical body in certain configurations.
- The centre of mass plays a critical role in the analysis of motion and dynamics.
- The centre of mass is important in sports and biomechanics for optimizing performance and balance.
Method to find the Centre of Mass of a Lamina
- Hang the lamina from a point.
- Hang a plumb line from that point.
- Draw a line down the lamina following the string of the plumb line.
- Hang the lamina from a second point.
- Repeat steps 2 and 3.
The point where the lines cross will be the centre of mass.
A third line can be drawn to confirm this location.
Examples
- The centre of mass of a uniform rod is at its midpoint.
- Athletes adjust their centre of mass to improve performance in activities like high jumping and gymnastics.