To know fully how a spinning top works there is a lot of physics involved, and some very nasty looking formulas to understand, like this for the derivative of angular momentum
However, this explaination is a very simplistic view of how a spinning top works, and there are whole PhD thesis’ on the true mechanics, but essentially it comes down to three things:
- How uniform the top is
- Friction it experiences (from the ground and air)
- The momentum it has
In Layman’s terms, a spinning top is staying upright because of the changes which happen as it spins. If you try to stand a top upright without spinning, it is possible, but very difficult. That is because it is incredibly hard to balance the top perfectly on such a small contact point. This means that any tiny differences in the weight of the top, or the way you hold it can knock it over. Imagine if the base of the top were a couple of centimetres wide, then you would have no problems balancing it right? That’s because the centre of gravity sits comfortably above the base, which is what is needed for something to stay balanced.
But on a spinning top we have a really small contact point on the ground; the margin for error on balancing is equally as tiny. This is where spinning comes in. what spinning does is it allows the imperfections of the balancing act to be spread out. Imagining the top in slow motion, and tilting to the right because one side is heavier than the other. Then, as the top spins that heavy bit is moving around and around the centre of gravity. So, when the heavier bit is on the left hand side, it all but balances out the tilt it caused on the right hand side.
The faster the top is spinning, the more dispersed the imperfections are, and therefore, the better the spin.
Generally a spinning top will have as small a point of contact with the ground as possible. This is due to the friction caused by its contact with the ground. If the contact point were large, then every rotation would cause a lot of friction, and slow the top down faster. And as we mentioned before, the top needs that speed to even out the imbalances it experiences.
The other factor that will keep a spinning top on its feet for longer is the momentum it has. The more momentum it has, the more energy it has and therefore the harder it is to stop. The two main stopping factors on a top are friction at the base, and the far more troublesome air resistance as it spins. The more momentum the top has, the more work the air needs to do to slow it down. To increase the momentum of a top the easiest method is to make the top heavier. As momentum is mass times velocity, the heavier the top, the more energy it carries. The problem then becomes keeping the velocity the same.
In a spinning top, all of the velocity comes from the hands of the spinner, so if the user is not able to put enough velocity into the spin, then it is not going to spin for very long. Similarly If the weight is too low, then it won’t spin for very long. This means the maker of the top needs to strike a balance between the amount of speed the user can put into the top, and how much it weighs.