Why are fuel cells used on space shuttles instead of batteries?

If a simple machine reduces the strength of a force, what must be increased?

The combining of light nuclei is called blank. blank as in not actually blank. you know what im tryin to say.

Which statement is true if the refractive index of medium a is greater than that of medium b? a. total internal reflection is possible when light travels from air to medium b to medium a. b. total internal reflection is possible when light travels from medium a to medium b. c. total internal reflection is possible when light travels from medium b to medium a. d. total internal reflection is possible when light travels from air to medium a. e. total internal reflection is possible when light travels from air to medium b.