#Helium #VacuumBalloon #AtmosphericPressure #Lift #Physics
🎈 Have you ever wondered about the science behind balloons and why helium balloons float? Well, my 9-year-old recently asked me a thought-provoking question: “If helium is lighter than air, would a balloon with a vacuum in it also float?” Let’s dive into the fascinating world of physics and find the answer to this intriguing question!
Understanding Helium and its Properties
To grasp the concept of why helium balloons float, it’s essential to understand the properties of helium and how they differ from those of regular air. Here are some key points to consider:
Helium is lighter than air: Helium is an inert gas that is lighter than the surrounding air, which is predominantly composed of nitrogen and oxygen.
Less dense than air: When we say helium is lighter than air, we are also implying that it is less dense. This lower density allows helium-filled balloons to defy gravity and float upwards.
Atmospheric pressure and lift: The concept of atmospheric pressure comes into play when discussing the floatation of balloons. The difference in pressure between the helium inside the balloon and the surrounding air creates buoyancy, resulting in the balloon floating.
Exploring the Hypothetical Vacuum Balloon
Now, let’s address the intriguing scenario of a balloon with a vacuum inside and whether it would float. Taking into account the hypothetical (rigid?) nature of the balloon, let’s delve deeper into the factors at play:
Surface area and volume: The atmospheric pressure acts upon the balloon with regards to its surface area and volume. When comparing a helium-filled balloon to a vacuum balloon of the same weight, the difference in pressure and density becomes a critical factor.
The role of air pressure: In the case of a vacuum balloon, the absence of helium or any gas inside the balloon changes the dynamics of atmospheric pressure. This absence of pressure differential may impact the balloon’s ability to float, as it lacks the buoyant force provided by helium.
Understanding Aerodynamics and Lift
To further comprehend the concept of lift and how it relates to the floating of balloons, let’s draw parallels to the principles of aerodynamics, particularly with respect to higher and lower air pressure:
Aeroplanes as an example: The way aeroplanes generate lift through their wings provides valuable insight into the role of air pressure. Higher pressure below the wing and lower pressure above the wing create lift, allowing the plane to defy gravity and take flight.
Applying the concept to balloons: While the mechanisms differ between aeroplanes and balloons, the fundamental principles of pressure differentials and buoyancy apply to both. The interplay of atmospheric pressure and the balloon’s density determines its ability to float.
In Conclusion
In conclusion, while a helium-filled balloon floats due to the lighter nature and lower density of helium compared to air, a balloon with a vacuum inside may not exhibit the same buoyant properties. The absence of a lighter gas or substance inside the balloon alters the pressure differentials, potentially impacting its ability to float.
The hypothetical scenario of a vacuum balloon presents a thought-provoking concept that underscores the intricate relationship between atmospheric pressure, density, and buoyancy. By understanding these fundamental principles, we gain valuable insights into the physics behind balloon floatation and the role of gases in defying gravity.
So, the next time you observe a helium balloon gracefully floating upwards, you can appreciate the scientific principles at play and the fascinating world of physics behind this simple yet captivating phenomenon! 🌍🎈🚀
Yes! If you could build a structure that stayed rigid under a vacuum, but that was still light, it would float. This concept is called a [vacuum airship](https://en.wikipedia.org/wiki/Vacuum_airship). They work, in theory, but in practice not so well.
All [lifting gases](https://en.wikipedia.org/wiki/Lifting_gas) work because they displace more mass of air than the mass of the object (this is really no different than how a boat floats- it is displacing more mass of water than the mass of the boat). In general, whether this is in air or water, we call this [bouyancy](https://en.wikipedia.org/wiki/Buoyancy).
So, a rigid sphere full of a vacuum could also displace more mass of air than it does, so it would also provide lift. However, this is impractical for several reasons. The first, in order to build something that can hold a vacuum, it would need to be a rigid structure, which in general is heavy. A balloon, on the other hand, the helium (or hydrogen, or other lifting gas) is under pressure, so provides the structure to the balloon. So, a very light piece of rubber is able to contain a bunch of helium, and thus the material itself is also light.
The other consideration is, a vacuum doesn’t provide much benefit over just using Helium or Hydrogen. I think a lot of people intuitively think that amount of lift you get is related to the ratio of the weights of the lifting gases (aka- since helium is twice as massive as hydrogen, then you might think hydrogen provides two times the lifting power as helium), but this isn’t the case. The lifting power is related to the difference in density between the air and the lifting gas. Because of this, hydrogen only provides 9% more lifting power than helium (that is, if you have two balloons and blow them up to the same size, but one with hydrogen and one with helium, the hydrogen balloon can only lift 9% more than the helium balloon can), and a vacuum balloon (assuming the container is only as massive as the balloon… in reality it’s much more), only provides 16% more lifting power than Helium. So that means, that if the structure you have to build to hold a vacuum weighs just 16% more than the balloon that holds the helium, then the advantage of using a vacuum is gone. But perhaps in the future, with carbon nano-tubes or some similar technology, we might be able to build a light enough structure to make it work.
in theory, yes.
in practice, we do not know how to create a container that can sustain the pressure differences of a vacuum that is light enough, for the effect to become reality.
But if we could hypothetically create, for example, a carbon nano-tube sphere that was stable enough to withstand the atmospheric pressure, it would likely float.
On a side-note, congratulations to raising a child with an inquisitive mind. Good job.
To float in a fluid (whether gas or liquid), the buoyant force is just proportional to the displaced fluid that would occupy the volume of that object.
If you fill a rigid balloon with nothing, then the buoyant force acting on it would equal the weight of the volume of air that would occupy its space.
Yep, however you’d need some kind of structure that prevents the balloon from not inflating, otherwise you’re just stuck with a flat balloon and making a structure that is both light enough and strong enough would be a bit difficult.
If the balloon was able to keep it’s structure, then yes, it would float. Density is the key metric here. A collapsed balloon has a lot of mass in a small volume (it’s dense). When it’s inflated, that mass is spread out in a larger volume (less dense). If it has a vacuum inside but can still occupy a larger volume, it’s even less dense and will float.
The term ‘lighter than air’ is a slight misnomer. It’s true that it’s lighter than air, but it’s that way because it’s less dense.
The kid is right. The problem, of course, is creating a rigid balloon that’s as light as a regular one yet capable of holding off a vacuum, ie negative one atmosphere or -15 pounds per square inch. It would need to be very strong indeed! In practical terms we cannot currently make such a lightweight thing sufficiently strong.
The helium or hydrogen or whatever, is serving as a placeholder to fill the space. That way you don’t need to hold negative pressure.
Yes but no
Vacuum is lighter than anything else you could fill it with. But you haven’t filled it with anything so the pressure difference is huge.
This usually causes the structure to collapse… And as the volume has decreased it will no longer float.
This works much better in water, as a Buoy.
The ONLY factor is density. That is all. More dense sinks, less dense floats. Everything finds its level. Oil less dense than water, floats on it. Helium less dense than ‘air’, floats.
Metal tank full of helium? Helium less dense than air, but compressing it to get more in there increases the density. The metal, however? Not less dense than air. Will not float.
Rubber balloon with only a little helium in it? Helium less dense than air, but rubber much more dense, aggregate exceeds air, sinks.
Rubber balloon with more helium in it? Helium less dense than air, enough to compensate for rubber’s density. Rubber also stretched thin, lowering its density overall. Floats.
Huge zeppelin sized tank full of helium? If overall it is less dense than air, it indeed will float.
Your question. Huge zeppelin sized tank full of…nothing? Well the air will try to collapse it. 100 miles of air is sitting on top of that tank, and it has places to go…if the vacuum isn’t using that space, the air wants to. So it has to be a rigid enough tank to not get squashed by the conveniently measured 1 Atmosphere of Pressure.
BUT! If it can achieve this? Remain rigid, and contain a vacuum, such that its overall density is lower than Air? It will absolutely float. That will be more buoyant than an equally sized tank of Helium, which still has mass and adds to the density. Vacuum adds NOTHING. The only problem is making it rigid. Helium achieves this with having a similar Pressure to the outside, therefore pushing back against the walls, but having less Mass than the air outside. (Pressure does not care about mass so much)
Nothing considered. If you had a vacuum and an indestructible ballon in it, filled with anything you like, it would stay in place. That is, until you consider a force acting on whatever is in your ballon. Buoyancy doesn’t exist without gravity, and while it might seem like a picky detail, some 9 year olds go on to study gravity.
When we say it’s lighter than air, it’s because the total enclosed volume is lighter than a similarly enclosed volume of air.
So, yes, a balloon full of vacuum would float, assuming you could stop it from collapsing.
> But it also relates to the atmospheric pressure upon the balloon with regards to its surface area and volume, right?
It’s Archimedes’ Principle. Go get a kitchen scale, some jars, and some weights, and test it in the bathtub!
*Any object immersed in a fluid is buoyed up by a force equal to the weight of the fluid displaced by the object.*
A full helium balloon displaces some volume of N2 and O2. That air weighs about 1.2 grams per cubic liter. Assume the balloon displaces 10 liters of air, that’s 12 grams of fluid that is displaced, about the weight of two quarters. If the ballon weighs 0.5g, and contains 10L of He2 which weighs 4 grams per 22.4L mole (PV=nRT) or about 2g, it can lift about 9.5 grams.
Go grab a 5 gallon bucket. An “empty” one. That bucket contains about 23 grams of air, about the same as four quarters. That 23 grams is the mass of the fluid your bucket would be displacing if you had a vacuum-filled bucket! Imagine how much air is contained in the volume of space that you move through when running. That’s the weight that you need to push aside when riding your bike fast, which is the source of all that air resistance!
Testing this with weights or vegetable oil (density ~0.9 times that of water) in the bathtub is a close approximation of what happens with gasses – it’s just a lot easier to contain and to measure.
If 2 rigid containers are the same volume, but one has helium and the other is pure vacuum, the helium one will weigh more. There’s literally just more molecules in it. As light as helium is, it doesn’t have negative weight. It has mass, which will be pulled by gravity.
This gets confusing in the real world, because helium is less dense that our sea level atmosphere, which means helium acts like it’s negative weight due to buoyancy. And “filling” a container with vacuum really means sucking out all of the air, which isn’t easy. I run a big vacuum chamber at work, it takes well over an hour to get down to an acceptable pressure. The lower you get the pressure the harder you have to work to get more air out. We just don’t see things under vacuum in our day to day lives very often, so people often have misconceptions about how things react to vacuums.
Yes.
That is also why steel boats float. Als long as the total object displaces more of the gas or liquid it is in, it floats.
The thing with balloons and light gas is that is is a simple way to make something float. Making a balloon that retains it’s shape while actually empty is super hard to do.
Yes, it would be even lighter than an helium-filled balloon (if you consider a balloon of the same volume, but rigid, “magically” keeping the form of a helium-filled balloon).
As the only thing that matters for buoyancy is for the displaced fluid (or gas) to be **heavier** than the volume displacing it, if you consider a bubble of void (thus, weighting NOTHING – or very next to nothing, if you consider that the “void” isn’t entirely empty), versus the same volume of air, it’s obviously lighter.
And thus, it will go UP.
Yes, but it’s not as big of an improvement as one may think. Helium is already very light compared to air.
– The density of air is 1.21 kg/m³
– The density of helium is 0.17 kg/m³
– The density of vacuum is zero, of course.
Every cubic meter of helium can lift 1.04 kilograms (since 1.21 – 0.17 = 1.04)
Every cubic meter of vacuum can lift 1.21 kilograms. That’s only 16% better than helium.
And this benefit would be completely dwarfed by the need of a heavy structure that can hold the pressure of the vacuum, while a helium balloon is easy and light.
Yes, but the issue is that it would be extremely hard to keep the balloon round, as it would be under pressure from all sides from the ambient air and would have no internal pressure to balance it. Basically it would deflate in an instant. The great advantage of using helium is that it counterbalances the surrounding pressure and keeps the balloon inflated.