Physics question for you smarties

[Holden McGroin]

Originally posted by mietla
It's not ice. It is a thin layer of water. The pressure you exert on ice changes the melting point and causes it to melt on contact.

December 2005 issue of Physics Today via the NYTimes

According to the frequently cited — if incorrect — explanation of why ice is slippery under an ice skate, the pressure exerted along the blade lowers the melting temperature of the top layer of ice, the ice melts and the blade glides on a thin layer of water that refreezes to ice as soon as the blade passes.

"People will still say that when you ask them," Dr. Rosenberg said. "Textbooks are full of it."

But the explanation fails, he said, because the pressure-melting effect is small. A 150-pound person standing on ice wearing a pair of ice skates exerts a pressure of only 50 pounds per square inch on the ice. (A typical blade edge, which is not razor sharp, is about one-eighth of an inch wide and about 12 inches long, yielding a surface area of 1.5 square inches each or 3 square inches for two blades.) That amount of pressure lowers the melting temperature only a small amount, from 32 degrees to 31.97 degrees. Yet ice skaters can easily slip and fall at temperatures much colder.

The pressure-melting explanation also fails to explain why someone wearing flat-bottom shoes, with a much greater surface area that exerts even less pressure on the ice, can also slip on ice.

Two alternative explanations have arisen to take the pressure argument's place. One, now more widely accepted, invokes friction: the rubbing of a skate blade or a shoe bottom over ice, according to this view, heats the ice and melts it, creating a slippery layer.

The other, which emerged a decade ago, rests on the idea that perhaps the surface of ice is simply slippery. This argument holds that water molecules at the ice surface vibrate more, because there are no molecules above them to help hold them in place, and they thus remain an unfrozen liquid even at temperatures far below freezing.

Scientists continue to debate whether friction or the liquid layer plays the more important role. Dr. Rosenberg, asked his opinion, chose a indecisive answer: "I say there are two major reasons."

   

[Sandman]

Originally posted by mietla
It's not ice. It is a thin layer of water. The pressure you exert on ice changes the melting point and causes it to melt on contact.

Take a block of ice and place the ends of it on two chairs, so the the block is suspended in the air (like the brick or a cement block for the karate chop). Now take a wire with weights on both ends. Place it over the block such that each weight is on the opposite side of the block. You'll see that with time the wire will cut through the ice and fall down below, but the ice block will remain in one piece.

The pressure the wire exerts, melts the ice beneath the wire causing it to slowly cut through, but the water immediatelly freezes above the wire (no pressure there), so the block remains intact after the experiment.

Nope.

As Holden wrote above... it's not that simple.

[LePaul]

Originally posted by Mustaine
no

the answer is 1.21 jigawatts

Ha Ha....dammit, coffee on the monitor...just saw the movie again Sunday.

[Sandman]

Originally posted by Mustaine
no

the answer is 1.21 jigawatts

On the USS Carl Vinson, there was this panel in one of the passageways and inside was a chronometer. We used to tell the noobs, that it was a flux capacitor and it was what allowed us to travel through time zones.

[airbumba]

Originally posted by Redwing
61221.6 J
or 61.2216 kJ
or 14621.83 calories

dT = Q / cp is the only formula you need


How about this one:
A hot air ballon has a volume of 2500 cubic meters and a takeoff weight (mass) of 250 kg. Outside temperature is 15 degrees C.
At what inside temperature will it take off?

Assume air is an ideal gas with a volume of 22,4 liters per mole and consists of 20% oxygen (O2) and 80% nitrogen (N2).

Don't know the answer off hand, and far too lazy to dig out some books, but a quick look at 'How stuff works...Hot air balloons"...I did discover this line....



"But nothing really got off the ground until the summer of 1783, when the Montgolfier brothers sent a sheep, a duck and a chicken on an eight-minute flight over France."


...I'll be dammned if there ain't a joke in there somewhere...lol.

Maybe the duck went " quack , quack", the chicken went "cluck, cluck"  and the sheep went, "that'll be ten bucks Bill".  

[BlueJ1]

I got this one, step back guys. The answer is...












Niner, followed closely by Egypt.


Thankyou. I'll accept any Nobel prize nominations.

[icemaw]

OUCH!!  That hurt

[SIZE=10]NO SOUP FOR YOU![/SIZE]

[Redwing]

Hey Wolfala, was I right? Ya solve mine yet (which was not homework... I get none )?

Lasersailor, so do I. Unfortunately, I need it a lot and since you posted a binary phase diagram some time ago I figure you do as well.

[AWMac]

Originally posted by Sandman
On the USS Carl Vinson, there was this panel in one of the passageways and inside was a chronometer. We used to tell the noobs, that it was a flux capacitor and it was what allowed us to travel through time zones.

Sandy my Father was on the Vinson and the ForestFire and the Connie...MM Division.  I got tired of livin all over and seeing Gun Metal Grey.. I left and joined the Army.  Pfffft...

Dad did 28 years in Navy, Me 20 years in Army... Army/Navy Game is GREAT in the Family, sux on phone bills....LOL

Mac

[Nilsen]

i miss homework

[Wolfala]

Originally posted by Redwing
Hey Wolfala, was I right? Ya solve mine yet (which was not homework... I get none )?

Lasersailor, so do I. Unfortunately, I need it a lot and since you posted a binary phase diagram some time ago I figure you do as well.

U were right. It wasn't homework - I was just bored and thought i'd get the OC brains engaged.

[lasersailor184]

Lasersailor, so do I. Unfortunately, I need it a lot and since you posted a binary phase diagram some time ago I figure you do as well.

Wasn't me who did that.  Are you talking about the steel phase diagram?  I think that was Mr. McGroin, but I'm probably mistaken.