|MadSci Network: Chemistry|
You need to first look at quite a few things:
- What is the density of air that is being filled in?
- How are you considering the sky (atmosphere)?
To understand an answer to this question, it is sufficient if you answer the questions above.
Density is a property of matter, that is the mass (or weight) of an object in an unit volume (unit volume=> 1 m^3 or 1 ft^3, etc.)
So if the gas that you filled it in with is lighter than air (like Helium, Hydrogen, etc.), then the tendency of that air is to move upwards. ( To understand this you'll need to get to the last part of the explanation.) If the weight of the balloon is nulled out by the effect of density, then the balloon will start to rise.
If the weighing is done on earth, then the object will tend to have a lower mass and weight. But this is just apparent weight. In reality all substances have mass, and when you add something to something else, you'll definitely end up with more. (Again, to understand this, please read the next paragraph, and get back and read this paragraph once again.)
You need to understand how the atmosphere functions. To understand it, think of the atmosphere as a big pool. If you get to the pool, and put something like styrofoam, it is going to float back up, the reason is that styrofoam is lighter than the same amount of water (density is lesser), but not massless. If you weigh it on land, it does weigh something, even though it is quite light, right. Now toss a penny into the pool, it is going to get to the bottom of the pool. The reason is that the penny is heavier than the same amount of water (density is greater.) In the same way all things stay down on the surface of the earth, because it is heavier than an equal amount of air. Air and Water are both fluids, and they behave in the same manner, This is one of the principles in fluids, that a lighter object than itself will tend to go up untill its density is equal to the density around it.
Thanks and Regard,
Abhilash J Markkassery,
Student, University of Texas at Arlington.
Try the links in the MadSci Library for more information on Chemistry.