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

[EX 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
[EX A]: What force is perpendicular to velocity and causes uniform circular motion?

[EX Q]: Passage: When heat is positive, the total energy of the system is increasing. Answer: it increases
[EX A]: What happens to the total energy of the system when heat is positive?

[EX Q]: Passage: An experiment is a controlled scientific test that often takes place in a lab. It investigates the effects of an independent variable on a dependent variable. Answer: an experiment
[EX A]:
What is a controlled scientific test that often takes place in a lab?