From the physics of g-force to weightlessness: what it feels like to fly into space

What does it take to go into space?

Besides money, hard work and a lot of moving parts, the answer is: science! This summer, NPR science podcast Short Wave launches Space Camp, a series about all the weird and wonderful things in our universe. We’ll start first with how to get to space.

Rockets and Isaac Newton

It usually goes without saying, but if someone wants to reach space, he or she has to be in some sort of spacecraft attached to a rocket.

That rocket releases exhaust fumes as it leaves the launch pad. That exhaust shoots towards the launch pad. This is where Isaac Newton’s third law of motion comes into play. This law states that “for every action there is an equal and opposite reaction.” So as the exhaust pushes down, it creates an upward force, causing the rocket to shoot up.

A good example on a smaller scale is a common physics demonstration where someone holds a fire extinguisher while sitting on something with wheels. Like in this video, as the extinguisher fires, the person goes in the opposite direction.

The exhaust fumes from a rocket shooting into space do the same thing.

The rocket has to go very fast because it has to overcome the curvature of spacetime itself. The fabric of our universe, called spacetime, can be thought of as a flexible sheet. The mass of the Earth causes the flat fabric of spacetime to curve inward in a funnel-like shape. Going up the funnel – and escaping Earth’s gravity – is more difficult than going down.

G-forces and why floating is falling

When those rockets fire, astronauts experience intense g-forces.

G-forces occur when your body experiences acceleration. If you just sit or walk around on Earth, you probably don’t notice them, even though there is always a regular pull of Earth’s gravity, which is 1 G.

You are more likely to notice them if, for example, you go up quite quickly in an elevator. Then you feel heavier.

But the severity of being in a high-speed elevator is nothing compared to what astronauts experience during a launch. Retired Navy captain and former NASA astronaut Wendy Lawrence recalled the feeling of intense g-forces in a recent interview with NPR.

“On my first flight, I remember thinking, ‘Oh my God, someone just sat on my chest,’” she says. “I was trying to see if I could put my arm out in front of me… and be like, ‘Wow, I can’t hold it up there against the tremendous force and acceleration produced by this amazing space vehicle.'”

That experience changes quite quickly. Once the rockets separate from the spaceship, the force pushing the astronauts into their seats is gone. They start floating under their seat belts.

They feel what is commonly called weightlessness.

But gravity has not disappeared. Even on the International Space Station, astronauts experience microgravity.

You can get a taste of this feeling on Earth. There are amusement park rides that shoot up – making riders feel heavy – and then drop riders. During that fall, the riders feel weightless, even though they are actually falling. In physics this is called free fall. All astronauts on the International Space Station technically fall very slowly, which is why they feel weightless.

Captain Lawrence says it’s a great experience. “You just relax,” she remembers. “You’re hanging there in mid-air and you want to park yourself in front of a window and float in front of it and watch the world go by.”

To revolve around the earth is to fall and miss the earth

It turns out that orbiting Earth, as astronauts do aboard the International Space Station, is falling. In concrete terms, it is heading towards Earth.

Newton had a series of thought experiments to explain this idea.

Scenario 1: Imagine that you are standing on a flat surface. Now imagine shooting a cannonball horizontally from your spot on the ground. In this scenario, the cannonball will travel horizontally for a while before beginning to fall along a curved path. This is projectile motion.

Scenario 2: You shoot the same cannonball horizontally – from the top of a very high mountain. In this case, the ball would have hit the ground even further away because it would have had to fall further and be in the air longer. If you shoot the cannonball at a higher speed, it would travel Furthermore. That curved path is being stretched further and further.

Scenario 3: With a high enough launch speed, you can drop the cannonball on a curved path that matches the curvature of the Earth. Because the curvatures match, the cannonball continues to miss the Earth. This is what it means to have something in orbit. The cannonball falls but never reaches the ground.

Preview of next week’s shortwave space camp: Pluto

Now as we leave Earth’s orbit and reach the end of our solar system, we will pass the beloved planet Pluto. Next week we ask ourselves: Why are there only 8 planets in our solar system? What does it mean that Pluto was downgraded to a dwarf planet all those years ago? We also explain why Pluto’s geology surprised scientists.

Do you have any other space stories you’d like us to discuss? Email us at kortgolf@npr.org.

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This episode was produced by Berly McCoy, edited by Rebecca Ramirez, and fact-checked by Regina Barber, Emily Kwong, and Rebecca. Gilly Moon was the audio engineer.