# Is there a terminal velocity for expansion in a vacuum?

• DWT
In summary, the expansion velocity of an object in a vacuum is reliant on the energy contained within the object and the vacuum itself does not have a pulling force. The expansion velocity will also be limited by the object's temperature as it cannot drop below absolute zero.
DWT
For this question imagine an balloon that will never pop and contains infinite mass. This balloon materializes inside a perfect vacuum with no boundary.

Is there a terminal velocity of the expansion of the balloon?

If so, does the balloon gradually accelerate to this velocity or does it hit it immediately?

If there is no terminal velocity then would the balloon accelerate to light speed and potentially beyond?

Assuming infinite mass is not reality. But if there is enough mass, it won't expand at all. It will collapse into a black hole.

If there is not enough mass for that, but if the skin of the balloon is elastic, expansion will stop when gas pressure balances elastic forces from the balloon.

If there is no balloon skin and not enough mass for a black hole, expanding gasses will stop accelerating when the molecules get too far away from each other to interact, so yes there would be a terminal velocity.

anorlunda said:

Assuming infinite mass is not reality. But if there is enough mass, it won't expand at all. It will collapse into a black hole.

If there is not enough mass for that, but if the skin of the balloon is elastic, expansion will stop when gas pressure balances elastic forces from the balloon.

If there is no balloon skin and not enough mass for a black hole, expanding gasses will stop accelerating when the molecules get too far away from each other to interact, so yes there would be a terminal velocity.

Infinite was an incorrect description sorry, I meant constant mass to volume. As the balloon expands mass materializes to keep a constant volume to mass ratio. As for the skin on the balloon let's say there is no elastic force or it also materializes as the balloon grows.

DWT said:
Infinite was an incorrect description sorry, I meant constant mass to volume. As the balloon expands mass materializes to keep a constant volume to mass ratio. As for the skin on the balloon let's say there is no elastic force or it also materializes as the balloon grows.

Physics deals with reality, you can't just wave your hands to ignore reality So no answer for that question as posed.

But you may have a real physics question. Can you ask it in a simple way to phrase it without the impossible balloon analogy?

DWT said:
As the balloon expands mass materializes to keep a constant volume to mass ratio.

Do you mean something like a multi-charge gun? What is the velocity of the additional mass? Is it already co-moving with the balloon or does it start at rest?

@DWT , are you trying to construct a scenario where the gas experiences constant accelerating force?

Your reference to light speed makes me think your question is about relativity, not expanding gas.

In other words, tell us better what your question is about.

anorlunda said:
@DWT , are you trying to construct a scenario where the gas experiences constant accelerating force?

Your reference to light speed makes me think your question is about relativity, not expanding gas.

In other words, tell us better what your question is about.

I guess my question may be as follows;

Is the expansion velocity of an object in a vacuum reliant on the energy contained within the expanding object (i will call this the pushing force) or does the vacuum have a "pulling force" on the object.

DWT said:
I guess my question may be as follows;

Is the expansion velocity of an object in a vacuum reliant on the energy contained within the expanding object (i will call this the pushing force) or does the vacuum have a "pulling force" on the object.
The vacuum has no pulling force.

In our day to day experience it feels as if it does - put your hand over the end of a vacuum hose, and it will certainly feel like the vacuum is trying to pull your hand in - but in fact it's the air pressure on the other side trying to push your hand in. In your expanding gas cloud, the pressure falls as the cloud expands, and when the expansion stops when the pressure becomes small enough that it can no longer force the gas farther out.

Also yes, the velocity is reliant on the energy contained within the expanding object. In the case of a gas such as in your original question, the temperature will drop as it expands, and the velocity of the expansion will be limited by that temperature since it can't drop below absolute zero.

## 1. What is terminal velocity for expansion in a vacuum?

Terminal velocity for expansion in a vacuum refers to the maximum speed at which an object can expand in a vacuum. It is typically measured in meters per second and is affected by factors such as the object's mass, surface area, and the density of the vacuum.

## 2. Is there a set terminal velocity for expansion in a vacuum?

No, there is not a set terminal velocity for expansion in a vacuum. It can vary depending on the object's properties and the conditions of the vacuum.

## 3. How is terminal velocity for expansion in a vacuum calculated?

Terminal velocity for expansion in a vacuum can be calculated using the formula v = √(2mg/ρAC), where v is the terminal velocity, m is the mass of the object, g is the acceleration due to gravity, ρ is the density of the vacuum, A is the object's surface area, and C is the drag coefficient.

## 4. Can terminal velocity for expansion in a vacuum be exceeded?

No, terminal velocity for expansion in a vacuum cannot be exceeded. Once an object reaches its terminal velocity, the forces of gravity and air resistance are balanced, and the object will continue to expand at a constant speed.

## 5. How does terminal velocity for expansion in a vacuum differ from terminal velocity in other environments?

Terminal velocity for expansion in a vacuum differs from terminal velocity in other environments because there is no air resistance present in a vacuum. In other environments, air resistance plays a significant role in determining an object's terminal velocity, while in a vacuum, only the object's mass and surface area are considered.

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