Two friends push with great force against a rock. The forces are equally strong but in opposite directions. A heavy box rests on top of the rock. Answer these questions about the motion of the rock. Assume that the rock is light enough for either friend to carry. What happens to the box when the friend steps away?

Nebulae are enormous clouds in outer space. they are made mostly of hydrogen gas, helium gas, and dust. some nebulae glow brightly, while others do not. the stars that people see are huge, bright balls of glowing gas. they are made mostly of hydrogen and helium. which statement correctly describes other ways in which nebulae and stars are different? a. stars can form inside a nebula but a nebula can never be produced by any star. b. a star always has a higher density than a nebula. c. stars can never form inside a nebula but a nebula can be produced by any star. d. a nebula always has a higher density than a star.