We can see each other in the classroom right now because we 

The planets never travel in a straight line as they orbit the Sun. According to Newton’s second law of motion, this must mean that

What does temperature measure?

How would you classify the following material? milk

Sodium, Na, atomic number 11, has only one valence electron. Upon losing this electron, what other atom in the periodic table does the sodium thus resemble?

Considering Einstein’s famous equation, E = mc 2, which of the following statements is true? 

On a cosmic calendar, in which the history of the universe is compressed into 1 year, when did the dinosaurs become extinct? 

A skater can spin faster by pulling her arms closer to her body or spin slower by spreading her arms out from her body. This is due to 

Grass is green because it absorbs green light, reflecting all other colors. 

The fact that the Voyager spacecraft continue to speed out of the solar system, even though its rockets have no fuel, is an example of