You are enjoying your breakfast after having put some salt on your scrambled eggs when your nerdy brother presents you with an ice cube floating in a glass of water and a short length of string. He challenges you to remove the ice cube from the glass using the string without tying any knots. What strategy do you use to remove the ice cube from the water glass?

Originally posted by haynewp
You are enjoying your breakfast after having put some salt on your scrambled eggs when your nerdy brother presents you with an ice cube floating in a glass of water and a short length of string. He challenges you to remove the ice cube from the glass using the string without tying any knots. What strategy do you use to remove the ice cube from the water glass?

use the salt. put some salt on the ice cube so that it melts a little, and touch the string to it, and get it to freeze on there.

Yes

How does it refreeze with the salt still mixed with the water on the cube?

Originally posted by haynewp
How does it refreeze with the salt still mixed with the water on the cube?

i wasn t too sure about this part. maybe i can put it in the freezer for a spell?

Here is the given answer:


Take the string and soak it in the water. Let the string rest across the ice cube. Reach across the table and get the salt that you used on your eggs; pour the salt over the string and the ice cube. The salt causes the ice to melt. However, when you stop pouring the salt, the water that formed on the top of the cube will refreeze with the string embedded in it. Now you can lift the ice cube with the string.


According to it, it will freeze when you stop pouring the salt, somehow.

What about this situation. U have an ice cube and a piece of string. U want to move the ice cube from one table to another (without it hitting the floor) using only the string. How do u do it?!

ps u are not allowed tie any knots!

Yeah, I'm confused bout the refreezing. Existence of salt (in this case, even when it's now dissolved in the water), IMO, will drop the freezing point, won't it?

Maybe the ice affects the immediate vicinity where you pour it, but, after some time, it diffuses into the rest of the glass, and the freezing point raises again at the desired site.

But it says 'the water that formed on the top of the cube will refreeze' as if it is the same water that contains the salt.

Originally posted by John Connellan
What about this situation. U have an ice cube and a piece of string. U want to move the ice cube from one table to another (without it hitting the floor) using only the string. How do u do it?!

ps u are not allowed tie any knots!

Can anyone answer this at all?!!! There IS an answer u know!

Press the string to the ice and let it be kept INSIDE the ice, then move it. Wrong? Someone says no...

Originally posted by curioucity
Press the string to the ice and let it be kept INSIDE the ice, then move it. Wrong? Sure.

Very good. I was going to say that the ambient temperature of the room was -5 Celsius but u have already explained how to get the string inside the ice! By pressing it. The pressure will actually melt the ice even if the temperature is below zero! The ice will then freeze over the top again when the pressure is released.

Isn't salt water denser than fresh water? So doesn't a layer of salt-free water cling to the string due to surface tension and freeze being that it is close to the ice, while the salt water defuses around the string? I'm just throwing out something.

Originally posted by John Connellan
What about this situation. U have an ice cube and a piece of string. U want to move the ice cube from one table to another (without it hitting the floor) using only the string. How do u do it?!

ps u are not allowed tie any knots!

Take the string, wrap it around your nerdy brother's finger, pull very hard and tell him you will not let go until he moves the ice cube to the other table.

Now that was easy, eh? I mean, obviously you cannot solve this problem with only string... something needs to move it :p

Originally posted by 4DHyperCubix
Now that was easy, eh? I mean, obviously you cannot solve this problem with only string... something needs to move it :p

LOL, with only the string being allowed touch the ice. Is that better?!

Nice try 4DHC :):D
And John, I forgot the term to explain the phenomenon, could you remind me? I think it's something like recrystalization or re- whatever......

Originally posted by curioucity
Nice try 4DHC :):D
And John, I forgot the term to explain the phenomenon, could you remind me? I think it's something like recrystalization or re- whatever......

I dont think theres a name for the phenomenon. It just happens coz water is funny. When u apply pressure to water (and thereby try to increase its density) the solid bonds break and it melts. As soon as u remove the pressure the water expands and freezes.

It is the basis behind being able to skate on an ice rink!

Umm, I'm not sure if it only happens to water....... excess pressure will cause solid material to slowly transform into liquid, and with the right temperature, the phenomenon may happen too..... Perhaps it also applies to even metals......

Originally posted by curioucity
Umm, I'm not sure if it only happens to water....... excess pressure will cause solid material to slowly transform into liquid, and with the right temperature, the phenomenon may happen too..... Perhaps it also applies to even metals......

I could be wrong but I always thought that applying pressure to a phase will (eventually) result in a phase change in the GAS -> SOLID Direction for most materials. Water being different though changes phase in the opposite direction in this case.

Originally posted by John Connellan
I dont think theres a name for the phenomenon. It just happens coz water is funny. When u apply pressure to water (and thereby try to increase its density) the solid bonds break and it melts. As soon as u remove the pressure the water expands and freezes.

It is the basis behind being able to skate on an ice rink! This is one of those scientific urban myths that keep popping up over and over, right up there with glass flowing in old windows and airplanes flying because of the Bernoulli principle.

Here's a simple demonstration to prove that pressure isn't what causes the ice to melt: get a large block of ice. Place two wires over it with different amounts of weight attached to the ends. You will find that the wires melt their way into the ice at the same rate regardless of how much weight they are supporting.

It's true that pressure causes an increase in temperature, but the effect is negligible in the case of an ice-skater or a string resting on an ice cube.

No its not that the wire melts through the ice which is the phenomenon!!! Its the fact that the ice freezes after the wire has passed through! The only variable is pressure.

Originally posted by Nasor
This is one of those scientific urban myths that keep popping up over and over, right up there with glass flowing in old windows and airplanes flying because of the Bernoulli principle.

Can I ask what's wrong with the explanation that aeroplanes flying due to the Bernoulli principle? Is it because the air moving over the top of the wing gets compressed, offsetting the decrease in pressure due to it moving faster? In that case, why do aeroplanes fly (and isn't it a bit stupid that they teach this in schools)?

Originally posted by Harsh
Can I ask what's wrong with the explanation that aeroplanes flying due to the Bernoulli principle? Is it because the air moving over the top of the wing gets compressed, offsetting the decrease in pressure due to it moving faster? In that case, why do aeroplanes fly (and isn't it a bit stupid that they teach this in schools)? Although air moving more quickly over the top of the wing does produce some lift from the Bernoulli effect, it exerts a trivial amount of force on the wing and would never produce enough lift to actually cause a plane to fly. The velocity difference of the air is far too low and air is too easily compressed for the Bernoulli effect to do much good. If you think about it, it's also unable to explain things like military jets that can fly upside down or aircraft that can fly with perfectly symmetric wings.

The vast majority of lift is generated via Newton's third law of motion; the shape of the wing and the angle at which it passes through the air causes the wing to deflect air downward, which in turn exerts an upward force on the wing. There are lots of other things that contribute to wing lift, but Newton's third law is the main one.

I don't know why to Bernoulli explanation is so popular with high school science text books when the actual explanation is much simpler and easier to understand.