Neil deGrasse Tyson Explains 'What Goes Up, Must Come Down'

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What goes up, must come down…right? Neil deGrasse Tyson says not so fast. You’ve heard the phrase before but Neil and comic co-host Chuck Nice are here to provide an update to this classic phrase in the latest StarTalk explainer video.

To start, we take a look at the science behind the phrase. You’ll learn about the forces of gravity working all around us. Then, Neil and Chuck discuss why it’s time to retire the phrase, or, make it a little more scientific.

We explore escape velocity. Discover more about traveling to the Moon and Mars and why we don’t pack fuel to get to the final destination, we just pack fuel to get to a certain point along the way. All that, plus, Neil and Chuck provide an updated version of “what goes up, must come down.”

About the prints that flank Neil in this video:

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About StarTalk:
Science meets pop culture on StarTalk! Astrophysicist & Hayden Planetarium director Neil deGrasse Tyson, his comic co-hosts, guest celebrities & scientists discuss astronomy, physics, and everything else about life in the universe. Keep Looking Up!

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"What doesn't reach escape velocity, Must come down"

ChrisSandtSmith

Chuck makes Neil’s information sound less like a lecture and more like a friendly conversation between friends! I happen to like the conversation! Thank you guys!

komranbehbehani

I would like a T-shirt that says, “what goes up at 6.9 miles per second must come down”

MrJim

This refers to my confidence when I see Neil it goes up and when I see an astrophysics problem it goes down😂😂

jagdishgohel

“What goes up, must come down”

Musk’s Falcon 9 rocket:
Hold my fuel.

mpatek

"That's pretty brilliant that people figured this out." "Yeah, it's called science." Lol! Great video

gyozakeynsianism

Through 8 months of covid19-quarantines, i have kept my self sane by watching the STATTALK channel on youtube, and i'm glad that i did, i learned alot, thank you guys for keeping all the space geeks updated.

obadaodeh

I love you Chuck but nothing makes me happier than when Neil asks you to do Math & you look like you just seen a ghost.

whackbag

Regarding air resistance - this a very important factor in rocket launches. If you watch any orbital rocket launch, you'll hear the announcer call out "Max Q" - Q is the letter assigned to air resistance. Rockets are designed for a certain maximum load of air resistance, so they have to take this in to account.

The faster something goes in a fixed air density, the more resistance it has.

But the higher something is, the thinner the air, so the less air resistance.

Max Q is the point that these two balance - while the rocket is continuing to accelerate, it has gone high enough that the combination of air thickness+speed produces the highest air resistance. Once it passes Max Q, the air is getting thinner faster than the rocket is accelerating.

Note that the Space Shuttle was capable of accelerating too fast! It had to throttle DOWN before reaching Max Q to slow its acceleration. Then once it passed Max Q, it would "go for throttle up".

Another common misconception is that space is "high up". It isn't. A large portion of the Earth's population lives closer to space than to an ocean. Live in Portland, Seattle, Chicago, Dallas? You're closer to space than to an ocean. The air thins out *REALLY* fast - conventional airliners fly at an altitude that has air pressure about one quarter that at Sea Level. Concorde flew at an altitude where air pressure was about 10% sea level. The SR-71 Blackbird spy plane experienced only about 5%. (Which is why Blackbird pilots wore what were basically space suits - they were being shot at, so if the plane lost cabin pressure, they would die quickly without a space suit.)

It is possible to achieve orbit at only 100 km (62 miles, 328, 000 ft) altitude - you're above enough of the atmosphere at that point that atmospheric drag won't produce heating from going orbital velocity. You are also still experiencing roughly 97% of the gravity at Sea Level, though! So if you just went straight up to 100 km, you would feel nearly the same pull down as on the surface. To stay in orbit, you have to be moving sideways fast enough that you're "falling back down" at the same rate as the curvature of the Earth is going away from you. That's all orbit is - going sideways fast enough to continually NOT hit the Earth.

Yes, there is some atmospheric drag at 100 km - enough that if you were put in to orbit there, the atmosphere would slow you down sufficiently to cause re-entry within a day or two. But not enough to be a serious heating concern.

(The lowest "commonly used" orbital altitude is 250 km - that's high enough for a spacecraft to remain stable for at least multiple months.)

AnonymousFreakYT

More accurate rephrasing can go like:
What goes up might come down
Or not

ramkoushik_vlogs

I already knew this, but still, getting such an entertaining refreshing of it is always nice. And i love to improve my english as a side effect.

madrooky

If YouTube and this guy were around when I was in highschool, I think I would have enjoyed science more.

I bet he had some great teachers.

trippplefive

Chuck catching an error on Neil's reasoning! Priceless!!

Fastball is about 140 feet per second, so close enough

pozzowon

I implore you great gentlemen to talk more about lightning

mjj

You guys have an awesome dynamic. Plus, I love how Chuck was like "uh uh uh..." and then called you out on not knowing baseball (even though Neil just had a baseball episode)

RPIdemon