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Name: Annie
Status: student
Grade: K-3
Location: Outside U.S.
Country: USA
Date: Winter 2009-2010

Question:
Can a helium balloon go up in space? If not, why?



Replies:
Hi Annie,

Good question, it shows that you are thinking.

The reason that a helium balloon goes up in the air is that it is being lifted by the air around it. The reason the air can lift up a helium balloon is that it so happens that the helium balloon is lighter than the air around it. It's like the way a stone will sink in water, but a piece of wood will not. The stone is heavier than the same amount of water, but wood is lighter than that same amount of water.

Now as we go higher into the air, there is less and less air - this, for example is why it is harder to breath as you get higher on a mountain. Because the air gets less, it also becomes lighter. So as the balloon rises, it will find less and less air - until the air around the balloon is just as heavy or as light as the helium balloon. At this point, the balloon can no longer go any higher because the lighter air can no longer lift it.

So in answer to your question, no, the helium balloon will never go into space because, the balloon can only be lifted by air, and that stops happening when the air gets thinner or lighter as the balloon goes higher.

Greg (Roberto Gregorius)
Canisius College


A helium balloon floats because it is lighter than air. As you go higher, towards space, the air becomes lighter the higher you go. Somewhere up there, the balloon is heavier than the air and cannot go any higher. This happens long before the balloon reaches space so a helium balloon can not get into space (unless an astronaut carries it with them and lets it go.).

R. W. "Bob" Avakian
Instructor
B.S. Earth Sciences; M.S. Geophysics
Oklahoma State Univ. Inst. of Technology


No. The reason a helium balloon floats in air is that it is surrounded by air, which is heavier than the balloon. In space, there is nothing heavier than the balloon to surround it. So, if a helium balloon were somewhere that has no air, such as on the Moon, it would sink. (Provided, that is, that the balloon were strong enough to keep from popping!)

Richard Barrans, Ph.D., M.Ed.
Department of Physics and Astronomy
University of Wyoming


A helium balloon rises because its "weight" is less than the "weight" of air that it replaces. There are two opposing forces, the buoyancy of the balloon pushing it up, and the force of gravity, pulling it back to the Earth. When the two forces, up and down, balance the balloon will neither rise nor fall.

This explanation assumes a set of conditions that may or may not be present: a still atmosphere (no wind), a constant temperature, and that the balloon is small enough that the change in barometric pressure is constant.

These conditions, especially the force due to gravity, will determine how high the balloon will rise.

Vince Calder


Hi Annie,

Thanks for a great question. The answer is that a helium balloon will not go up to space.

The reason a helium balloon floats is the same reason as a ball floats in water. The ball is less dense than the water, so it floats. And, the helium is a unique gas that is less dense than air, so it actually floats in air.

But, as it rises, as you get higher in the atmosphere, the air gets thinner, which means the air's density decreases. Eventually the balloon will get to a point where its the air's density has dropped to be equal with the balloon's density. At that point the balloon no longer 'floats' and can climb no higher.

(note to parent/teacher - density is often hard for kids to understand because they confuse weight and density. one good way to teach the difference is to get two objects of similar size, but different weight. a good example might be a 40mm steel ball and a 40mm ping pong ball. then get two objects that weight the same but have different volume such as a pillow and the same steel ball.)

Another question might be why the balloons do not stay up in the air forever. The first reason is that the helium slowly leaks out of the balloon. Over time, it loses enough helium to make it fall back to earth. Another reason why the balloon will not get to space is that it is very cold up in the atmosphere, and a normal rubber balloon would crack or rip, again losing its helium and coming back to earth.

(note to readers/parent/teacher - the balloon expands to equilibrate pressure, which also can cause it to tear; air pressure also plays a role in the size of the balloon, but I would guess that concept is too advanced for K-3)

Hope this helps,

Burr Zimmerman


Hi Annie -

In space a helium balloon will be a nice plump pillow, but it will not have any floating power, no "buoyancy".

A balloon can go up to the edge of space, if you are careful to make it out of a big limp bag that is 90% empty when you launch it from the ground. Sometimes you see pictures of balloons like that. As the balloon rises from the ground, the air gets thinner, and the air pressure around the balloon gets lower, and the helium inside that balloon expands a lot. Most balloons pop themselves when the gas expands too much. The too-big limp bag allows lots of expansion before popping happens, so it goes up above 90% of the air, and looks completely full when it gets there. Up there, there is not much air left in the sky above the balloon, so the sky above the balloon is dark blue or black instead of light blue or white. That is about as high as helium balloons can go.

Even if it could expand forever, a helium balloon floats because its helium molecules inside are lighter than the air molecules outside. Far out in space, the few molecules you find are hydrogen molecules, not air, and helium molecules are heavier than hydrogen molecules, not lighter. So even a forever-expanding balloon would sink back down to the top of the air and float there, like a bubble on top of an invisible ocean.

Jim Swenson


Annie

A helium balloon will not go up into space.

It will only go as high to the point where the density of gas inside the balloon is the same as the density of the air on the outside. That is, the balloon rises because it weighs less than the air around it, and it will stop rising when it reaches the height in the atmosphere where the weight of the air outside the balloon equals the weight of helium inside the balloon (per unit volume).

As you go higher and higher in the atmosphere, the air weighs less and less because there is less air on top of it weighing it down.

Sincere regards,
Mike Stewart



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