Unwanted gear shifting?
I'm a teen and know basically nothing about bike mechanics and repair, so I wanted to throw this question out.
My problem is... Just recently, the pedals on my new (used) bike have started shifting forward (as if I were changing a gear) when I don't touch the gear control at all. I don't actually end up in a new gear, but it's pretty annoying. Right now it's only when I'm in my top (or hardest gear), but I don't know- it might spread. I was using my dad's bike before this and the problem was even worse.
Is there some simple solution to this?
Or do I just ruin every bike I seem to ride?
p.s. when responding, remember i might not know the exact name of any parts you might refer to...