Centre of Mass | GCSE Physics | Doodle Science

GCSE Science

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Script:
The centre of mass of an object is the point where the entire weight of an object appears to act. Working out the centre of mass of a symmetrical object is easy; it’s simply the point where the lines of symmetry cross.

However it’s very unlikely that you’ll be dealing with such perfect shapes so you work it out by suspending the object freely, along with a plumb line. The centre of mass is always below the point of suspension, so by marking the vertical along the plumb line you know the centre of mass is somewhere along that line. By suspending the object from another point and repeating the process, you get two lines that intersect and the point of intersection is the centre of mass.

The position of the centre of mass is very important when it comes to the stability of an object. For example, a double decker bus is built to have a very low centre of mass and a wide base so that the line of action of its weight stays within the base when it goes around a sharp corner. If something has a high centre of mass combined with a small base then it is very unstable and will topple over with minimal effort.

A plumb line is an example of a simple pendulum. All it consists of is a weight attached to a piece of string that can swing freely. The time taken for it to swing from one side to the other and back again is called the time period. The time period of a pendulum of the same length is always the same no matter what height you release it from, which is what makes them so good at keeping time. The time period and the frequency are related by the formula: T = 1/f. So if a pirate ship at a theme park swung with a frequency of 0.2Hz then the time period would be 5s, which is one scary ride!

References:
1. http://www.bbc.co.uk/education/subjects/zrkw2hv
2. CGP GCSE Physics AQA Revision Guide.

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