Question: if i got a pvc pipe 5cm wide and place negative magnets in it (almost a pipe in a pipe) and put a negative magnet at one side that is closed so nothing can get through would the magnet shoot out fast or slow

Electrical charges are referred to as negative and positive, but magnetic poles are usually referred to as ‘North’ and ‘South’.

So your idea is that if you put two of the same pole together the magnets will repel and if they repel fast enough you could make a cannon to launch magnets! A very cool idea, but unfortunately the magnets would come out rather slowly.

The speed that the magnet shoots out depends upon the strength of the magnets. With the types of magnets you can get easily, the magnet inside your pipe will shoot out quite slow. The stronger the magnets the faster the one in the pipe will shoot out.

Strong magnets are usually electromagnets, which means that instead of having a piece of magnet you have a coil of wire and you put large amount of electricity (electrical current) through it. The more current you use the stronger the electromagnet. In your case using an electromagnet also means you can switch it on and off, which gives you a trigger for your cannon. The problem is that the more electrical current you use the hotter the coil gets and eventually it melts.

Lots of people (and militaries) have tried to use magnets to launch projectiles and the main problems are that you need very very strong magnets, which usually have to be very heavy and expensive. You also need very large electrical currents to drive the magnets which again is very expensive and requires special metals to make the wire for the coils.

Even after all that, things shot by magnet are slower than things shot by explosives, which are cheap. So people stick to explosives.