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Technology / Re: How does shifting the COG affect torque needed to rotate about a fixed fulcrum?
« on: 24/12/2015 10:43:36 »
We are off to a good start here because you clearly understand the concept of torque and leverage, that the effective force depends on the distance from the fulcrum.
OK, let's think about a flywheel. Start with a bicycle wheel, I think you will agree that if you have 1kg of lead and place it close to the hub it will be easier to spin the wheel compared to if you place the same weight out at the rim. The wheel will also spin longer. The principle here is inertia.
When we push a weight in a straight line we recognise it has inertia, F=ma, greater the force, greater the acceleration, greater the mass the less easy to accelerate.
When pushing a weight in a circle the force has to be replaced by torque to take into account the leverage. But the mass also has to be effectively increased to take account of this leverage effect. In a rotating system the 'torque equivalent' of mass is the moment of inertia I, which is the actual mass x radius squared I=mr2.
So the distance we place the mass from the fulcrum has a much greater effect than the effect of placing the force at the same distance. This is why when designing a flywheel we try to put the mass as far away from the pivot point as possible to get greater Inertia.
Hope that helps.
OK, let's think about a flywheel. Start with a bicycle wheel, I think you will agree that if you have 1kg of lead and place it close to the hub it will be easier to spin the wheel compared to if you place the same weight out at the rim. The wheel will also spin longer. The principle here is inertia.
When we push a weight in a straight line we recognise it has inertia, F=ma, greater the force, greater the acceleration, greater the mass the less easy to accelerate.
When pushing a weight in a circle the force has to be replaced by torque to take into account the leverage. But the mass also has to be effectively increased to take account of this leverage effect. In a rotating system the 'torque equivalent' of mass is the moment of inertia I, which is the actual mass x radius squared I=mr2.
So the distance we place the mass from the fulcrum has a much greater effect than the effect of placing the force at the same distance. This is why when designing a flywheel we try to put the mass as far away from the pivot point as possible to get greater Inertia.
Hope that helps.
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