Unit 7 facts about forces The Moment of Force

Now what I thought I might do today… What we are going to talk of is the extension of a force. We’re going to talk about the moment of a force.

If I apply a force to something, then I find that that force will turn or at least it will try to turn a particular object. It will turn, revolve. So that turning tendency is called a moment, the turning moment of the force. And if I want to measure that turning moment, the turning moment will depend on the size of the force itself. The bigger the force is the bigger the turning effect. But equally the further away the force is from the pivot. … If you can think of a spanner … If you have a short spanner and you try to loosen a bolt or a nut, it might be extremely difficult but if you got a longer spanner you would get what we would call leverage and you would get a bigger leverage. You would get a bigger turning moment.

So the turning moment, the moment depends on the force itself … and the distance … and the distance. It is the force multiplied by the distance. But what you have to remember is that it is the perpendicular distance that we’re going to measure. In fact – I’m not going to ask you take it down – we would say that the moment of the force is the product of the force and the perpendicular distance between the line of action of the force and the fulcrum, the turning point.

Moment is equal to force times distance. This, incidentally, you have in your notes. Something simple to illustrate. If we take the drawing of a spanner … The drawing of a spanner there. We apply a force at the end there, your pivot or the turning point, or as we call the fulcrum, is in the center there. Now the moment of that force is that force (F1) multiplied by the perpendicular distance (D1).

Unit 8 gravity, friction and magnetism

A lot of things in the universe can be measured, but people want to know why they are that size. We know the mass of a quark and the charge on an electron. These are constants. It turns out that these numbers have to be exactly what they are, because if they were different we would not be here. You, me and the physicists, we’re part of the universe. We have to be here to make physics, so physics has to describe a universe where there can be people. Gravity is another problem for physics - because it is everywhere and acts on everything, including space itself. It’s different from other forces like electricity or radiation, because you can’t stop it or turn it off.

Modern physicists still look mostly at things we can’t see. (They think gravity might happen because of something no-one has ever detected called the Higg’s boson.) Either very small things in quantum physics or very big things like galaxies. Putting them together is the main problem of modern physics. The universe and space and time described by Einstein and the fuzzy fast-moving little sub-atomic particles and small things that might make them up. If you want to know how the universe began - with a tiny size but very big mass, then you need a theory that fits both together. At the moment, the theory suggests that the things we can see – stars and planets etc. make up only 5% of the universe. The rest is 25% “dark matter” and 70% “dark energy”.