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

[Q]: Passage: When you use a machine, you apply force to the machine. This force is called the input force. The machine, in turn, applies force to an object. This force is called the output force. The output force may or may not be the same as the input force. The force you apply to the machine is applied over a given distance, called the input distance. The force applied by the machine to the object is also applied over a distance, called the output distance. The output distance may or may not be the same as the input distance. Answer: output force
[A]: What do you call the force a machine applies to an object?

[Q]: Passage: Equinox comes halfway between the two solstices. At equinoxes, the Sun's rays shine most directly at the Equator ( Figure below ). The daylight and nighttime hours are exactly equal on an equinox. The autumnal, or fall, equinox happens on September 22 or 23. The vernal, or spring, equinox happens March 21 or 22 in the Northern Hemisphere. Answer: equinox
[A]: What event occurs between the two solstices?

[Q]: Passage: A chemical reaction occurs when some substances change chemically to other substances. Chemical reactions are represented by chemical equations. Answer: chemical reaction
[A]:
What occurs when some substances change chemically to other substances?