Guns in Space

TL;DR

Guns in space illustrate how gravity, orbital speed, fusion, and cosmic expansion shape a projectile’s path. An object must travel over 17,000 mph, or 8 km per second, to orbit Earth, while a lunar bullet would need about 1,600 m/s. Water would make the Sun brighter rather than extinguish it, and an intergalactic bullet could never catch receding galaxies. Read on for the explanations behind each outcome.

Transcript

Hey, Vsauce. Michael here. And what do you say we get outta here...to space and into an orbit. That way we could just float around and be free from the influence of gravity. Except not really. Astronauts orbiting around the Earth experience pretty much the same gravitational pull that you and I are feeling right now. The major difference is that th... Read More

Key Insights

• 💨 Orbiting is simply falling at a fast enough speed that the curvature of the Earth falls away.
• 😤 The speed needed to orbit Earth is around 17,000 mph or 8 km per second.
• 🛰️ Objects in orbit around the Moon can complete an orbit at a much lower speed than on Earth.
• 💦 Fusion reactions in the Sun are much more powerful than chemical bonds in water, and adding mass to the Sun would cause it to burn brighter and faster.
• 💨 Shooting material into the Sun in a way that spreads it out would prevent fusion reactions from occurring.
• 💆 Adding mass to the Sun would decrease its lifespan, as more mass means a hotter burn and a shorter life.
• 👾 Shooting a bullet in inter-galactic space would result in it being forever alone, as the universe is expanding too quickly for it to reach receding galaxies.

Questions & Answers

Q: What happens if you fire a gun in space?

The outcome depends on where the gun is fired. Near the Moon, a sufficiently fast bullet fired toward the horizon could orbit and eventually hit the shooter, while in intergalactic space a bullet could never catch galaxies receding from it.

Q: Why do astronauts float in orbit if Earth’s gravity still pulls on them?

Astronauts in orbit experience nearly the same gravitational pull as people on Earth. They float because they are constantly falling toward Earth while moving horizontally fast enough for Earth’s surface to curve away beneath them.

Q: How fast must an object travel to orbit Earth?

An object must travel at over 17,000 mph, or about 8 km per second, to fall around Earth without hitting it. Traveling that fast through the atmosphere would likely cause it to incinerate from air friction.

Q: Could a bullet fired on the Moon orbit and hit the shooter?

Yes, a powerful enough gun fired toward the lunar horizon could send a bullet around the Moon. After waiting, the shooter could be struck in the back of the head by that same bullet.

Q: How fast would a bullet need to travel to orbit the Moon?

Henry calculated that the bullet would need to travel about 1,600 m/s. The Paris gun fires at exactly that speed, according to the transcript.

Q: Would shooting water at the Sun put it out?

No, adding water would increase the Sun’s mass, causing it to burn hotter, brighter, and faster. The Sun is powered by hydrogen fusion rather than ordinary fire, and fusion operates on a much more powerful scale than the chemical bonds in water.

Q: How would adding 20 solar masses of water affect the Sun?

Adding 20 solar masses of water would shorten the Sun’s life expectancy. The transcript says it would fall from the current 5 billion years to only a few hundred million more years.

Q: Why would a bullet fired in intergalactic space never reach another galaxy?

A few megaparsecs from the nearest galactic cluster, galaxies would become about 200 km farther away every second on average because the universe is expanding. Since a bullet travels only a few kilometers per second, it could never catch those receding galaxies.

Summary & Key Takeaways

• Astronauts orbiting the Earth experience the same gravitational pull as us but are constantly falling towards Earth while moving horizontally fast enough that they stay in orbit.

• On the Moon, objects can complete an orbit at a much lower speed than on Earth due to its smaller size.

• Adding water to the Sun would not put it out as fusion reactions in the Sun are much more powerful and adding mass would cause it to burn brighter and faster.