How to Calculate How Many Helium Balloons David Blaine Needed

Pretty much everyone loves balloons—especially younger children. Kids are slowly building up ideas about the way the universe works (through their observations), and they already know that when you let go of something, it falls. Oh, but the helium-filled balloon is a rule breaker. It goes UP. It just seems magical.

Older people still have a hidden fascination with these balloons. Each of us at some point has considered the question: How many of these would I need to lift me off the ground? Well, that’s exactly what David Blaine did for his latest stunt, which he called Ascension. He used a bunch of large balloons to lift him up to an altitude of 24,000 feet. At that point, he detached himself from the balloons and used a parachute to get back down.

I think the best part of the stunt was the initial launch. The team set up the balloons so that there was a near perfect balance between the buoyancy force from the balloons and the gravitational force pulling Blaine down, such that he mostly just floated there right above the ground. (He did have some people holding on to him to make sure he didn’t drift up and away prematurely.) Then, so he could begin his journey upward, his daughter added one more balloon, and he handed her a weight he’d been holding. It’s a pretty cool way to ascend.

But now for the questions and answers.

Why do helium balloons float?

Balloons don’t float with magic. Instead, it’s a result of gravity and the atmosphere. Yes, it’s true. A balloon wouldn’t float without gravity.

Let’s imagine the atmosphere as a bunch of balls—except these balls are actually molecules of mostly nitrogen along with some oxygen. Each of these balls are moving around with some average velocity, and they are being pulled down by the gravitational interaction with the earth. So, you could think of these gas balls just like a tennis ball tossed across the room, except that they are super tiny. Oh, and there’s a bunch of these balls. That means that they interact with other gas balls. You can think of these interactions as though they were collisions. It’s all of these ball-ball collisions that keeps them from just ending up on the ground. Also it would be terribly awkward if all the air pooled down on the lowest level, because then you couldn’t breathe.

blue moving balls
Illustration: Rhett Allain