frictional forces slowing down a rolling soccer ball the magnetic force pulling paper clips to a powerful electromagnet the magnetic force pushing two magnets apart the force of gravity acting on raindrops that fall to Earth
I gave my students this multiple choice question: Which type of force requires contact between two objects for one to push or pull the other?

Only one answer is correct among these 4 choices:
- frictional forces slowing down a rolling soccer ball
- the magnetic force pulling paper clips to a powerful electromagnet
- the magnetic force pushing two magnets apart
- the force of gravity acting on raindrops that fall to Earth

Could you tell me which one is correct?

frictional forces slowing down a rolling soccer ball