Which of these is an indication that a chemical reaction has occurred?

1) melting of a substance

2) boiling of a substance

3) formation of a precipitate

4) freezing of a substance

In a bumper car arena, two cars of equal mass are heading straight toward each other. the orange one is traveling at a speed of 5 meters per second. the green one is traveling at a speed of 2 meters per second. which of the forces most affects the motion of the bumper cars after they collide? a) gravity b) friction c) the other car d) wind resistance

Ais not a compound machine. a. bolt b. shovel c. handcart (dolly) d. see-saw (teeter totter)

Lin yao looks at the back of a spoon. how should she describe her reflection? upside down and smaller upside down and larger right-side up and smaller right-side up and larger