Floating hourglass

[Genady]

Why does the hourglass not start rising right away?

 

[exchemist]

1 hour ago, Genady said:

Why does the hourglass not start rising right away?

 

Spoiler

When top heavy it tilts  against the side of the cylinder, which acts as a brake. As the weight is transferred to the lower compartment this effect diminishes, allowing it to rise.

 

Edited September 10, 2023 by exchemist

[Genady]

@exchemist, your answer is correct. +1.

Edited September 10, 2023 by Genady

[TheVat]

1 hour ago, Genady said:

Why does the hourglass not start rising right away?

It is sleepy.  

[Genady]

4 minutes ago, TheVat said:

It is sleepy.  

It is heavy headed.

[swansont]

Spoiler

The falling sand is exerting a force on the bottom of the hourglass. This decreases as the sand build up, as the falling sand has less momentum when it hits

 

[Genady]

48 minutes ago, swansont said:

  Reveal hidden contents

The falling sand is exerting a force on the bottom of the hourglass. This decreases as the sand build up, as the falling sand has less momentum when it hits

 

Spoiler

If it were so, the effect would depend on a size of the passage in the hourglass and would even disappear if the flux of the sand is small enough. In fact, it does not.

 

[md65536]

3 hours ago, swansont said:

  Hide contents

The falling sand is exerting a force on the bottom of the hourglass. This decreases as the sand build up, as the falling sand has less momentum when it hits

 

However, the sand's momentum is gained while in free-fall, not contributing to the weight of the hourglass. As the sand builds up, the falling sand has less momentum, but there's also less sand falling.

When the hourglass is started, there is sand falling weightlessly, and no sand hitting the bottom, and the hourglass briefly weighs less. At the end, there is sand hitting the bottom but no more of it falling, and it is briefly heavier. The start and end are similar to standing on a scale holding some mass, letting go of it, and then catching it lower down. https://demoweb.physics.ucla.edu/content/110-weight-hourglass

But I see other links claiming experimental verification of different results.

[Genady]

4 minutes ago, md65536 said:

However, the sand's momentum is gained while in free-fall, not contributing to the weight of the hourglass. As the sand builds up, the falling sand has less momentum, but there's also less sand falling.

When the hourglass is started, there is sand falling weightlessly, and no sand hitting the bottom, and the hourglass briefly weighs less. At the end, there is sand hitting the bottom but no more of it falling, and it is briefly heavier. The start and end are similar to standing on a scale holding some mass, letting go of it, and then catching it lower down. https://demoweb.physics.ucla.edu/content/110-weight-hourglass

But I see other links claiming experimental verification of different results.

Spoiler

The fact is that if before the hourglass starts rising the sand flow stopped, e.g., the passage got clogged, the hourglass would stay on the bottom.

 

[swansont]

@Genady, you are making claims that are not in evidence. Can you share it?

[Genady]

I just add information as if you make an experiment and get the result. My only evidence is a detailed explanation of what is happening, but that would ruin the puzzle.

[swansont]

46 minutes ago, md65536 said:

However, the sand's momentum is gained while in free-fall, not contributing to the weight of the hourglass. As the sand builds up, the falling sand has less momentum, but there's also less sand falling.

I’ve read that the flow rate is pretty much constant in an hourglass, except at the very end. There is less sand falling because the distance it falls decreases. It’s not like a liquid, where the flow rate depends on the column height. It’s part of why hourglasses are useful.

Only a small fraction of sand is in freefall.

 

9 minutes ago, Genady said:

I just add information as if you make an experiment and get the result. My only evidence is a detailed explanation of what is happening, but that would ruin the puzzle.

But all we have to go by is this video. What is the source of the additional information? How does one disprove an explanation? There are studies that show the extra apparent weight of an hourglass.

[Genady]

4 minutes ago, swansont said:

But all we have to go by is this video. What is the source of the additional information? 

A full video. Several of them.

I can stop interfere and just tell you, that this answer is wrong and think of another one. Or I can suggest a mental experiment, like this:

Spoiler

What do you think would happen if the hourglass was placed instead of the bottom of the tube, on the bottom of an aquarium or a pool? How the process would be different?

It could suggest the answer without more videos perhaps.

[swansont]

If you drop something on a scale, it will initially register more than the weight of the object. How does one disprove this as the effect?

[Genady]

1 minute ago, swansont said:

If you drop something on a scale, it will initially register more than the weight of the object. How does one disprove this as the effect?

Spoiler

if before the hourglass starts rising the sand flow stopped, e.g., the passage got clogged, the hourglass would stay on the bottom of the tube

 

[TheVat]

My post, though joking, was a hint.  So was Genadys reply.

Watch the video very closely.