It really doesn't depend on the burning, other than the fact that burning away the toothpick is a smoother way of eliminating the mass than most other things you could do. Losing half of the toothpick probably shifts the center of mass toward the tines of the forks by a hundred microns or so, but that's almost certainly less than the width of the rim on the glass, so it won't make a difference in the balance. Each of those forks has a mass of about 35 grams, while the toothpick has a mass of less than one gram. So shouldn't burning half of the toothpick away shift the center of mass? Yes, but by a trivial amount. If you place that bit of the toothpick on the rim of the glass, and eveything is wedged together securely, then you're supporting the forks-and-toothpick object from a point directly under its center of mass, and it should balance there happily. This is the reason why it's possible to balance the two forks on the rim of the glass in the first place. The midpoint of that would be about halfway out the toothpick. In the case of our wedged-together forks, you can estimate the position of the center of mass by saying that it ought to be at about the midpoint of a line connecting the centers of mass of the two individual forks, which is the dotted line shown in the diagram. Notice that nothing in that recipe requires the center of mass of an object to be inside the object- it can perfectly well be a point floating out in space, and in fact it is for any horseshoe-shaped object. Then, you add all those terms together, and divide by the total mass of the object, which will give you a position. The center of mass of an object is found by breaking the mass of the object down into lots of little pieces, and multiplying each piece by its distance from some reference point.

The two forks stick together to form a sort of very broad horseshoe shape, as seen here: Now, when you wedge the two forks together with the toothpick, you can treat the resulting thing as a single extended object, with its own center of mass. The toothpick in that picture is roughly at the position of the center of mass. Using that trick, I located the center of mass for a couple of forks, shown here: The balance point for an extended object will be directly below the center of mass of that object. If you're going to throw it through the air, for example, the center of mass will trace out a nice, simple parabolic path, regardless of what sort of tumbling or flailing motion is going on with the rest of the object.Ī quick-and-dirty way to locate the center of mass of a given object is to try to balance it on your finger. The key concept here is the idea of the 'center of mass' of a system, which is basically the point at which you consider all the mass to be concentrated if you need to treat an extended object as a point particle. It's a nifty demonstration of some physics principles, so I thought I would explain how it works, with a couple of pictures (several of her commenters have the right idea, btw). Burning the toothpick does not change the the centre of gravity, so the cutlery doesn’t fall.Last week, GrrlScientist posted a cool video showing a trick with two forks and a toothpick: The centre of gravity is found over the edge of the glass because of the way the fork and spoon go down and towards the middle. This is because of the centre of gravity, which is the middle point where something can be balanced. Even though the toothpick is just on the edge of the glass, the entire thing remains balanced.

You could knock any remaining burnt pieces into the water. The toothpick will stop burning once it gets to the rim of the glass. You could also light the other end (the one past the fork and spoon) if you wanted to.

Using the matches, light the end of the toothpick that is over the water.

You might have to angle the toothpick towards the spoon, and you will probably need to use a point near the end of the toothpick.

Using the toothpick, balance the cutlery on the edge of the glass.

Place a toothpick in between the middle of the fork’s prongs.Push the fork and spoon together so the spoon goes over the two inside prongs and under the two outside prongs.The glass needs to have some water in it for weight.Perform a magic trick using science! Balance a fork and a spoon on the edge of a toothpick, with the other end of the toothpick just touching the rim of a glass.

Toothpick magic trick