What force causes a balloon to float?

In summary, when a CO2 balloon is blown, the rubber+CO2 is heavier than air and falls under the influence of gravity. When helium is used in a balloon, the rubber+helium is lighter than air and does not fall under the influence of gravity.
  • #1
timothychoi
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When I blow a balloon with CO2, it falls as it is heavier than air. Then it is gravity that causes the balloon to fall.
When I buy a balloon filled with helium gas from a store, it floats as it is lighter than air. But what force is causing the balloon to float?
 
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  • #2
timothychoi said:
When I blow a balloon with CO2, it falls as it is heavier than air. Then it is gravity that causes the balloon to fall.
When I buy a balloon filled with helium gas from a store, it floats as it is lighter than air. But what force is causing the balloon to float?
https://en.wikipedia.org/wiki/Buoyancy

:smile:
 
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  • #4
timothychoi said:
I see. It is like an airplane.
No, more like a Blimp...
 
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  • #5
berkeman said:
No, more like a Blimp...
Oh. I noticed that an airplane floats by "lift". Thanks.
 
  • #6
timothychoi said:
Oh. I noticed that an airplane floats by "lift". Thanks.

an aeroplane doesn't float by lift it flies, air must move across the wings ( above and below) to cause lift
If it doesn't keep moving, it will stall and fall from the sky
 
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  • #7
timothychoi said:
When I blow a balloon with CO2, it falls as it is heavier than air. Then it is gravity that causes the balloon to fall.
When I buy a balloon filled with helium gas from a store, it floats as it is lighter than air. But what force is causing the balloon to float?

The force causing the balloon to rise is also gravity! It is not like an airplane. It is more like a bubble under water. Gravity is pushing the water down. As the bubble goes up, that amount of water goes down. So the bubble going up is effectively water falling. Of course gravity is pulling down on the air in the bubble too, but with less force because it is lighter than an equal volume of water. So in net the bubble rising is equivalent to something (the difference in weight between the water and the air) falling.

With your CO2 balloon the rubber+CO2 is heavier than an equal volume of air and that difference in weight falls under gravity. With helium the rubber+helium is lighter than an equal volume of air, and, again, that difference in weight falls under gravity.

That is an energy argument. The way this works in detail is that the weight of the water causes a pressure gradient. The water on top has no weight pressing down on it. Below the surface the water is being pushed down by the weight of all the water above that depth. The deeper you go the greater the weight above and the higher the pressure. That means that the bubble experiences a higher pressure on the bottom of the bubble than on the top. There is a net force upward. It can be shown that the net force upward is equal to the weight of the missing water. This is called buoyancy. If the contents of the bubble weigh less than the missing water, the net force of buoyancy + gravity is upward, and vice versa.
 
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FAQ: What force causes a balloon to float?

1. What is the force that causes a balloon to float?

The force that causes a balloon to float is called buoyancy. This force is a result of the upward pressure exerted by a fluid, such as air, on an object immersed in it.

2. How does buoyancy work to make a balloon float?

Buoyancy works by exerting an upward force on an object that is partially or fully submerged in a fluid. This force is equal to the weight of the fluid displaced by the object, and it acts in the opposite direction of gravity, causing the object to float.

3. Why do some balloons float while others do not?

The ability of a balloon to float depends on its density compared to the density of the surrounding air. If the balloon is filled with a gas that is less dense than air, such as helium, it will float. However, if the balloon is filled with a gas that is more dense than air, it will sink.

4. How does the shape of a balloon affect its ability to float?

The shape of a balloon can affect its ability to float in several ways. A larger balloon with a larger surface area will displace more air and therefore experience a greater upward force, making it more likely to float. Additionally, a more streamlined shape can reduce air resistance and help the balloon to rise more easily.

5. Can the temperature of the air affect a balloon's ability to float?

Yes, the temperature of the air can affect a balloon's ability to float. Warmer air is less dense than colder air, so a balloon will experience a greater upward force in warmer air. This is why hot air balloons use heated air to rise and stay aloft.

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