Ask a physicist anything. (2)

[catzrfluffy]

What's that scene where he drinks a cup of tea, where the teacup is cut in half, but the tea stays in - how do they do that?

 

[pgp_protector]

What's that one where he drinks a cup of tea, where the teacup is cut in half, but the tea stays in - how do they do that?

Where who cut's a teacup in half?

If you're talking about a magician, it's a secret and we're not allowed to tell you.

 

[Wiccan_Child]

What's that scene where he drinks a cup of tea, where the teacup is cut in half, but the tea stays in - how do they do that?

Who?

 

[catzrfluffy]

Willy Wonka, it's a scene in the film. Sorry.

 

[pgp_protector]

Willy Wonka, it's a scene in the film. Sorry.

Ahh
Then in that case

What's that scene where he drinks a cup of tea, where the teacup is cut in half, but the tea stays in - how do they do that?

Computer Graphics.

 

[catzrfluffy]

In 1970 something?

 

[Doveaman]

Does this make any sense:

"The usual demonstration using heavy steel balls on a rubber sheet to represent ‘gravity wells’ relies on gravity as its own explanation!"

 

[catzrfluffy]

What's a gravity well? If I drop a bucket in, how much gravity will I draw up?

Is there a way to soften water at home?

 

[pgp_protector]

In 1970 something?

Sorry I was thinking the more recent version

I'd have to see the old one, but I'd hazard to guess that there was some glass or something for the side of the cup.

 

[Cabal]

What's a gravity well?

Essentially any region in a gravitational field that requires an input of energy to escape from.

This could be something local like trying to kick a ball up out of a pit in the ground (a gravitational potential well) or try to boost a rocket to escape velocity out of Earth's gravitational reach (which is also a well).

If I drop a bucket in, how much gravity will I draw up?

You won't draw up gravity, but the bucket's gravitational potential energy will change (the exact amount depends on your point of reference, potential energy in fields like gravity is a relative thing).

Is there a way to soften water at home?

Depends how persistent the hardness is, but simple solutions are boil the water or use a softener like Epsom salts.

 

[Cabal]

In 1970 something?

Could well be Chroma Key (blue/greenscreen). That's actually pretty old, iirc

 

[Wiccan_Child]

Does this make any sense:

"The usual demonstration using heavy steel balls on a rubber sheet to represent ‘gravity wells’ relies on gravity as its own explanation!"

I noticed that myself actually. The rubber-sheet model only works because a mass is pulled down by gravity, creating the indentation.

Of course, it's an analogy. There isn't really a massive rubber sheet in space. Mass is what warps spacetime, not gravity.

What's a gravity well?

An imaginary 'dip' in space. If you imagine space as a flat sheet, then a massive object will create a dent in that sheet. This dent is the gravity well. It's an important concept because, like real wells (or valleys, etc), you need energy to go 'up' the sides. And conversely, you're compelled to slide down to the bottom.

Earth's gravity well pulls us into the centre (i.e., the middle of the Earth), much as a sledge slides down a snowy hill.

If I drop a bucket in, how much gravity will I draw up?

Three litres.

Is there a way to soften water at home?

Beat it with a rock until it's tenderised.

 

[canehdianhotstuff]

Boiling water will not make is softer. You would have to install a water softener, usually ion exchange. Takes out the calcium for sodium.

 

[Cabal]

Boiling water will not make is softer. You would have to install a water softener, usually ion exchange. Takes out the calcium for sodium.

Hard water - Wikipedia, the free encyclopedia

Temporary hardness is caused by a combination of calcium ions and bicarbonate ions in the water. It can be removed by boiling the water or by the addition of lime (calcium hydroxide). Boiling promotes the formation of carbonate from the bicarbonate and precipitates calcium carbonate out of solution, leaving water that is softer upon cooling.

As I said, it depends on the hardness - and it's not a great solution as you end up with limescale everywhere, but it does soften it up a little.

Water softeners are the best solution though of course

 

[Doveaman]

An imaginary 'dip' in space. If you imagine space as a flat sheet, then a massive object will create a dent in that sheet.

We could only imagine this sheet if we imagined gravity pulling down on the object to create the dent in the sheet.

As far as our imagination can see, it is gravity causing the dent, and not the dent causing the gravity.

This dent is the gravity well. It's an important concept because, like real wells (or valleys, etc), you need energy to go 'up' the sides. And conversely, you're compelled to slide down to the bottom.

That's because gravity is acting upon us independently of the well.

Even apart from the well we still need energy to go 'up' or be compelled to stay down.

Earth's gravity well pulls us into the centre (i.e., the middle of the Earth), much as a sledge slides down a snowy hill.

So the earth is in the gravity well of the universe, and we are in the gravity well of the earth.

If the earth has its own gravity well, then where's the dent?

 

[Dr Doofenshmirtz]

We could only imagine this sheet if we imagined gravity pulling down on the object to create the dent in the sheet.

That's one reason I don't like the allegory (get it? allegory) of the rubber sheet. Simply because those who don't understand that it's an allegory don't get it
Therefore the rubber sheet explanation fails (although I understand it, and get it)

Your thinking is one-dimensional
You are only thinking of "down" (possibly due to to the simplistic picture of the rubber sheet allegory, therefore possibly thinking that gravity is pulling the planet "down") regarding the rubber sheet allegory, and in so thinking, you are not thinking correctly.

Think "up" and "sideways" gravity wells at the same time as the "down" well, and you might just start to get it (just as an introduction. I could go on....but just for now, try to grasp that concept, it's not that hard)

 

[Cabal]

Is the better way of visualising it to think of say water flowing round a marble? There'll be a little shell of disturbance around a spherical object.

(Btw, apologies for getting gravity well and potential well mixed up earlier)

 

[Doveaman]

That's one reason I don't like the allegory (get it? allegory) of the rubber sheet. Simply because those who don't understand that it's an allegory don't get it
Therefore the rubber sheet explanation fails (although I understand it, and get it)

Your thinking is one-dimensional
You are only thinking of "down" (possibly due to to the simplistic picture of the rubber sheet allegory, therefore possibly thinking that gravity is pulling the planet "down") regarding the rubber sheet allegory, and in so thinking, you are not thinking correctly.

Well, it's not my fault. It's the rubber sheet's fault. I'm just trying to make sense of it.

Isn't science supposed to provide the "best" explanations? If this is the best you've got, I just don't get it.

Think "up" and "sideways" gravity wells at the same time as the "down" well, and you might just start to get it

Is this supposed to be an improvement?

You are asking me to imagine "up" wells and "sideways" wells at the same time as "down" wells?

I'm trying really hard, but all I can come up with are caves and tombs and the craters on the moon, not wells.

(just as an introduction. I could go on....but just for now, try to grasp that concept, it's not that hard)

No thanks. I'm confused enough already.

 

[Doveaman]

Is the better way of visualising it to think of say water flowing round a marble? There'll be a little shell of disturbance around a spherical object.

The marble would also be pushed in the direction of the water flow. Is that the direction we are all going?

Or are you talking about water flowing from all directions onto the marble?

This would require water flowing down onto the top of the marble, and water flowing up onto the bottom of the marble.

In other words, this would require magical water.

 

[Cabal]

The marble would also be pushed in the direction of the water flow. Is that the direction we are all going?

Or are you talking about water flowing from all directions onto the marble?

This would require water flowing down onto the top of the marble, and water flowing up onto the bottom of the marble.

Flowing....around the marble, I guess. I wasn't thinking of it moving necessarily.