Detailed Instructions: Given a scientific passage and an answer, generate a question for the given answer.
Q: Passage: Even if Laura didn't try to stop the skateboard, it would stop sooner or later. That's because there's also friction between the wheels and the pavement. Friction is a force that counters all kinds of motion. It occurs whenever two surfaces come into contact. Answer: friction
A:
What force occurs whenever two surfaces come into contact?