What is an element? 1. A substance made of more than one type of atom.
2. A substance that is made of water.
3. A substance that is made of no atoms.
4. A substance made of only one type of atom.

22. the top of a cliff is located a distance h above the ground. at a distance h/2 there is a branch that juts out from the side of the cliff, and on this branch a bird's nest is located. two children throw stones at the nest with the same initial speed, one stone straight downward from the top of the cliff and the other stone straight upward from the ground. in the absence of air resistance, which stone hits the nest in the least amount of time?