Pitter-patter in Newton’s footsteps
One of the fastest ways to find out how little you know is repeatedly to ask the question, “Why?” This practice has become a quality-management fad. Nevertheless, asking why-why-why is actually fun to do in real life, it’s good mental exercise, and it’ll help you achieve that smaller hat size you’ve been meaning to get into.
I thought I’d see what my 4½-year-old son had to say when I saw him playing with a helium balloon last night. First, we established that there was gas both inside and outside the balloon. Then we talked about what a gas is and how it relates to liquids and solids. (There was a short digression when he said that steam is what rises from a fire.) Then we got into the matter of how lighter stuff floats up and heavier stuff sinks down.
The next “Why?” brought us—already?—to where the sidewalk ends for me: the weakest of the four fundamental forces of nature. But I asked him the question anyway. “When you jump into the air, why do you always come back down again instead of shooting off into space?”
The reply: “Because I don’t have wings!”
Don’t let the terminology of gravitons and GUTs fool you: this is as good an answer as any physicist can give you. 
