PHYS 120 Assignment 2 average score 6.9

The following is a quote from Chapter 8, A Ride on a Lion, in the book Sylvie and Bruno by Lewis Carroll the author of Alice in Wonderland. The quote was sent to me by my daughter who took this course several years. Between Emily typing the quote and my twiddling with it to “correct” what I perceived of as typos or omissions, the quote may be a tad different than the original but the spirit of the quote has remained intact.

After reading through the quote carefully, discuss whether or not you think Lewis Carroll got the “physics” correct. In particular what do you think about the underlined passages?

"How convenient it would be," Lady Muriel laughingly remarked, a propos of my having insisted on saving her the trouble of carrying a cup of tea across the room to the Earl, "if cups of tea had no weight at all! Then perhaps ladies would sometimes be permitted to carry them for short distances!"

"One can easily imagine a situation," said Arthur, "where things would necessarily have no weight, relatively to each other, though each would have its usual weight, looked at by itself."

"Some desperate paradox!" said the Earl. "Tell us how it could be. We shall never guess it."

"Well, suppose this house, just as it is, is placed a few billion miles above a planet, and with nothing else near enough to disturb it: of course it falls to the planet."

The Earl nodded. "Of course though it might take some centuries to do it."

"And is five-o'clock-tea to be going on all the while?" said Lady Muriel.

"That, and other things," said Arthur. "The inhabitants would live their lives, grow up and die, and still the house would be falling, falling, falling! But now as to the relative weight of things. Nothing can be heavy, you know, except by trying to fall, and being prevented from doing so. You all grant that?"

We all granted that.

"Well, now, if I take this book, and hold it out at arm's length, of course I feel its weight. It is trying to fall, and I prevent it. And, if I let go, it falls to the floor. But, if we were all falling together, it couldn't be trying to fall any quicker, you know: for, if I let go, what more could it

do than fall? And, as my hand would be falling too--at the same rate--it would never leave it, for that would require it to get ahead of it in the race. And it could never overtake the failing floor!"

"I see it clearly," said Lady Muriel. "But it makes one dizzy to think of such things! How can you make us do it?"

"There is a more curious idea yet," I ventured to say. "Suppose a cord was fastened to the house, from below, and pulled down by someone on the planet. Then of course the house goes faster than its natural rate of falling: but the furniture--with our noble selves--would go on failing at their old pace, and would therefore be left behind."

"Practically, we should rise to the ceiling," said the Earl. "The inevitable result of which would be concussion of the brain."

"To avoid that,” said Arthur, "let us have the furniture fixed to the floor, and ourselves tied down to the furniture. Then the five-o'clock-tea could go on in peace."

"With one little drawback!”, Lady Muriel gaily interrupted. "We should take the cups down with us: but what about the tea?"

"I had forgotten the tea," Arthur confessed. "That, no doubt, would rise to the ceiling unless you chose to drink it on the way!"

"Which, I think, this is quite nonsense enough for one while!" said the Earl.

Answers

, and with nothing else near enough to disturb it: of course it falls to the planet."

This describes and imaginary universe with a planet and a house and nothing else near enough to disturb either. Given that, the house will feel a gravitational pull towards the planet and fall. This is correct physics.

Nothing can be heavy, you know, except by trying to fall, and being prevented from doing so. You all grant that?"

This is also perfectly good physics. In fact, very insightful physics. When you stand on a scale and read your weight, the scale works because it is keeping you from falling? If you glued the scale to your shoes and stepped off the edge of a building, the scale would read zero because you and it would fall at the same rate.

it would never leave it, for that would require it to get ahead of it in the race. And it could never overtake the failing floor!"

You and book are falling toward the planet at the same rate so from your perspective, the book remains stationary. Again, the physics is correct.

"Practically, we should rise to the ceiling,"

The force of the rope pulling on the house would be in addition to the gravitational force of the planet leading the house to fall at a larger rate than it did before the force of the rope was added to gravity. Consequently, the contents of the house would fall at a slower rate and “float” toward the ceiling. Lewis Carroll got it right again.

We should take the cups down with us: but what about the tea?"

The tea would float out of cups and probably form a blob of tea held together by the forces between water molecules.