Does Balloon Lift Force Increase or Decrease with Altitude?

In summary, as a helium balloon ascends, the density of the air inside and surrounding it decreases due to the equation p=p0*exp(-z/z0) where z0 is the scale height of the atmosphere. This results in a decrease in lift force acting on the balloon. However, this effect can be counteracted by the balloon reaching colder upper layers and the helium contracting, causing the balloon to descend. It is possible for balloons to cross long distances before all the helium leaks away, assuming the atmosphere goes on forever and the balloon is made of infinitely stretchable material.
  • #1
the keck
22
0
As a helium balloon increases in altitude, the density of the air inside decreases. However, the density of the air surrounding it (The atmosphere) also decreases
with altitude p=p0*exp(-z/z0), where z0 is the scale height of the atmosphere. So does this mean the lift force acting on the balloon decrease?p=p0#exp(-z/z0)
P=P0#exp(-z/z0) (Pressure decreases with altitude)
PV=nRT

The puzzling thing I find with this problem is this, if both the density of the helium inside the balloon and the air surrounding it decreases with increasing altitude, would this mean that the balloon could rise forever, since these effects cancel each other out i.e. the life force will stay the same as the initial lift force when it left the Earth's surface? (Assuming the atmosphere goes on forever, and the balloon is made of material that is infinitely stretchable i.e. can expand forever and not break)Thanks...I hope the problem is clear enough for you all to understand

Regards,
The Keck
 
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  • #2
In theory yes, actually as the balloon ascends it reaches colder upper layers the helium contract and the balloon descends.
It is possible for balloons to cross intercontnaental distance before all the helium leaks away.
 
  • #3
Observatory Science Team

I would like to clarify that the lift force on a balloon does not stay the same as it rises in altitude. While it is true that the density of the air both inside and surrounding the balloon decreases with altitude, the decrease in density of the surrounding air has a greater effect on the lift force than the decrease in density of the helium inside the balloon.

This is because the lift force on a balloon is a result of the difference in density between the surrounding air and the helium inside the balloon. As the balloon rises and the surrounding air becomes less dense, the difference in density decreases, resulting in a decrease in lift force.

Therefore, as the balloon continues to rise, the lift force will eventually decrease to the point where it is equal to the weight of the balloon and it will reach a state of equilibrium, where it will no longer rise. This is due to the fact that as the balloon rises, the density of the surrounding air decreases faster than the density of the helium inside the balloon, leading to a decrease in lift force.

In summary, the lift force on a balloon will decrease as it rises in altitude due to the decrease in density of the surrounding air having a greater effect on the lift force than the decrease in density of the helium inside the balloon. This is a well-known phenomenon in the field of aerodynamics and is taken into account when designing and launching balloons.
 

1. What is the principle behind the change in balloon lift force with altitude?

The change in balloon lift force with altitude is due to the variation in air density. As altitude increases, the air density decreases, which means there are fewer air molecules per unit volume. This results in a decrease in the buoyant force acting on the balloon, causing it to lose lift force.

2. Is the change in balloon lift force consistent at all altitudes?

No, the change in balloon lift force is not consistent at all altitudes. Initially, as the balloon rises, the air density decreases rapidly, causing a significant decrease in lift force. However, as the balloon continues to rise, the decrease in air density becomes less significant, resulting in a slower decrease in lift force.

3. How does the temperature affect the change in balloon lift force with altitude?

Temperature plays a significant role in the change in balloon lift force with altitude. As the temperature decreases with increasing altitude, the air density also decreases, causing a decrease in lift force. However, if the temperature remains constant, the change in lift force will be more consistent.

4. Does the shape or size of the balloon affect the change in lift force with altitude?

Yes, the shape and size of the balloon can affect the change in lift force with altitude. A larger balloon will displace more air molecules, resulting in a greater buoyant force. Additionally, the shape of the balloon can also impact the amount of air it displaces and, therefore, the lift force it experiences.

5. How does the weight of the balloon affect the change in lift force with altitude?

The weight of the balloon does not directly affect the change in lift force with altitude. However, a heavier balloon will require more lift force to overcome its weight, making it more difficult for the balloon to rise. As a result, the balloon may not reach higher altitudes, where the air density is lower, and the lift force is decreased.

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