Given a scientific passage and an answer, generate a question for the given answer.

[Q]: Passage: Figure 6.11 The frictional force supplies the centripetal force and is numerically equal to it. Centripetal force is perpendicular to velocity and causes uniform circular motion. The larger the F c , the smaller the radius of curvature r and the sharper the curve. The second curve has the same v , but a larger. Answer: centripetal force
[A]: What force is perpendicular to velocity and causes uniform circular motion?

[Q]: Passage: What does sunshine have to do with sleep (other than the sun shining in your eyes and waking you up)? For many people, sleeping problems have to do with an amine that the brain makes called melatonin. This compound affects the sleep-wake cycle and is affected by sunlight. During the winter, the daily cycle of melatonin production may be affected by less sunlight hours. If this cycle is changed, the person may have trouble sleeping. Melatonin supplements are available in pharmacies and health food stores and may be of help for those with sleeping problems. Answer: melatonin
[A]: During the winter, production of what amine involved in the sleep-wake cycle may be affected by less sunlight hours?

[Q]: Passage: Most sedimentary rocks form from sediments. The sediments must be packed together to form a rock. Sedimentary rocks also form as minerals precipitate from saline water. Sedimentary rock formation is described in the next concept. Answer: sediments
[A]:
Most sedimentary rocks form from what?