For most kids, the period right after lunchtime was spent fighting off sleep and boredom. But that was never a problem for Peter and Mary because that was when their favorite class (science) was taught by their favorite teacher (Mr. Medes). So they would eagerly finish their lunch and head into the classroom early, just to see what Mr. Medes had planned for the day’s lesson. Today was no exception; actually, Peter found it easier than usual to finish lunch early given what Mary was eating.
“Ugh! How can you stand eating that?” he asked.
“What’s the matter with peanut butter and bologna sandwiches?” Mary replied. “I don’t make fun of your tofu crunch. Anyhow, we astronauts need to be able to eat almost anything.”
“No, you need to be able to keep it down once you are in space,” Peter retorted. “I wonder what that feels like?”
“Dunno. But let’s go ask Mr. Medes; he can probably tell us.” The two gathered up the debris from their lunches, sorted out the recyclables before depositing them in the appropriate bins, and headed to class.
“Welcome, welcome!” aid Mr. Medes. “You are just in time! I need someone to help me water the hydroponics lab.”
Peter and Mary grabbed a couple of watering cans and filled them with water. As they wandered around the room filling the various containers filled with plants, water, and the occasional fish, Peter asked the question that was on both their minds. “Mr. Medes, what is zero gravity? What does it feel like?”
“That’s an interesting question. Would you believe me if I told you that you’ve already felt it?”
“No way!” Mary said. “We don’t have a zero gravity room!”
“Neither does NASA; we cannot control gravity, no matter what TV shows and movies say,” was Mr. Medes calm reply. “Instead, NASA simulates zero gravity, or ‘zero G’ for short. But we need to see what zero G looks like before you can understand how the simulations work.”
“How will we do that?” Peter asked.
“Simple. Let me grab a paper cup and I’ll show you.” Mr. Medes rummaged through his supply cabinet for a moment before coming up with a paper cup and a pencil. “For the first part of the experiment, let’s pour some water into a paper cup. What will happen?”
“That’s easy,” Mary replied scornfully. “The water will stay in the cup.”
“Right. But why?”
“Because gravity holds it in!” Peter said.
“Right again. Now let’s poke a hole in the bottom of the paper cup using the pencil. What will happen next?”
“Gravity will pull the water out of the cup through the hole,” Mary answered.
“Let’s see,” said Mr. Medes. Holding the paper cup over the sink, he punched a hole in the bottom. As soon as he removed the pencil, water started to gush out the bottom. “You are right. Gravity pulls down on the water and the cup. But, because the cup is stationary, only the water can move. Now let’s see what happens in zero gravity.”
Putting his finger over the hole in the bottom of the cup, Mr. Medes refilled it with water. “I’m going to take my finger away from the hole and let go of the cup. What will happen?”
“The cup will fall,” Peter said.
“And the water will run out,” Mary added.
“Let’s see if you are right,” Mr. Medes replied. “On the count of three. One, two…”
What do you think will happen? Do the experiment!
“Three!” Mr. Medes removed his finger from the bottom of the cup and let go. Both Mary and Peter watched in astonishment as the cup fell and the water stayed inside all the way down.
“Hey! What happened?” Peter demanded.
“That was zero G in action,” Mr. Medes replied. “Gravity pulled down on the water and the cup together at the same rate. Because the water and the cup were moving together, the water stayed inside the cup.”
“But what does that tell us about zero G?” Mary asked.
“Do you remember the other name for zero G?” Mr. Medes asked.
“Free fall!” the two chorused as they began to understand.
“Right! Most scientists prefer to call it free fall because gravity is still there; you are just freely falling.”
“So free fall feels like,” Peter began.
“Falling freely!” Mary finished. “So if we jump, we are in free fall!”
“Right again,” Mr. Medes said. “But NASA doesn’t like to make its astronauts jump up and down. In the first place, it looks silly. And, more importantly, you don’t get a very long period to practice in.”
“So what do they use?” Mary asked.
“Well, for big things, they use a swimming pool. By adding the right amount of weights, they can make the astronauts and their tools ‘neutrally buoyant’; that is, they neither rise to the top of the pool nor sink to the bottom. They call the place the Neutral Buoyancy Laboratory.”
“That must be a big pool!” Peter said.
“The largest in the world!” Mr. Medes replied. “But that doesn’t tell astronauts what real zero gravity feels like. Only freely falling can do that. So they take the astronauts up in a modified airplane and fly a path like a roller coaster. As the plane falls toward the ground on a long parabolic arc, everything inside it is falling at the same rate and so they are in free fall. But then they have to pull up to avoid hitting the ground and everything feels a couple of Gs of acceleration.”
“Wow! Is that the plane that they call ‘The Vomit Comet’?” Mary asked.
“Yes, it is. And can you think of something here at school that takes you on a long smooth arc?”
Mary puzzled over it for a moment before saying “swing sets!”
“Right again!” Mr. Medes smiled down at them. “As you swing back and forth, you go over a path much like the one flown by the Vomit Comet. At the bottom, you are changing your direction of movement from down to up. You feel that as a little extra tugging on you. And at either end, you are in free fall for just a moment.”
Glancing at the clock, he added “And you have just enough time before class starts to go try it out if you want to.”
Not needing a second hint, the two ran out of the room to practice being astronauts.