Quarters on Dry Ice

Classical Mechanics Level 2

If you place a quarter at room temperature in a block of dry ice (as above), the quarter will vibrate as though it is shivering. Why does this happen?

Image Credit: YouTube Taras Kul .

Warmth from the quarter heats the dry ice, causing it to change from a solid to a gas The molecules of the quarter warm up, which cause it to vibrate The surface of the dry ice slowly collapses due to the weight of the quarter

2 solutions

Guy Alves
Apr 3, 2017

It's pretty well known that dry ice tends to sublimate at room temperature, and as the carbon dioxide escapes, it jostles the quarter.

(Fun fact: Dry ice CAN melt into liquid carbon dioxide; it's just that atmospheric pressure isn't great enough to allow it.)

If this experiment is done in a pressurized chamber, will the quarter still vibrate the same way?

Rohit Gupta - 4 years, 2 months ago

It would in actuality. But, not prominently

Nikhil Waiker - 4 years, 1 month ago

Why do you think so? Can you elaborate why it won't be prominent?

Rohit Gupta - 4 years, 1 month ago

Dan Ley
Apr 9, 2017

Just to clarify, dry ice is actually the solid form of $CO_2$ .

Dry ice sublimes naturally (converts straight from solid to gaseous form) at about $-109^\circ$ Fahrenheit, so you could imagine that the coin is relatively warm enough to produce quite a high sublimation rate.

Lots of $CO_2$ evaporating creates a small air current, where the seeping gas pushes the coin back and forth.

What if we use a plastic coin instead of the metal coin? Will the plastic coin also shiver the same way?

Rohit Gupta - 4 years, 2 months ago

By my logic, yes. I'm guessing the answer is no, haha. Because plastic isn't a thermal conductor like metal is?

Dan Ley - 4 years, 2 months ago

I agree with you, plastic won't sublimate the dry ice as rapidly as the metal would. Due to this, the carbon dioxide will seep slowly.

Rohit Gupta - 4 years, 2 months ago

The CO2 turns in to sold to gas. The gas moves the coin.

Saam Amerat - 4 years, 1 month ago

I cannot dispute your reason for the dry ice sublimating; I dispute that the warmth (relative heat) contained in the coin is the cause of the gas generation. Shortly after contact the coin becomes isothermal with the solid. The coin itself is enveloped in a cloud of gas at vaporization temperature. It is the weight of the metal alone that is adding energy to the system that is being converted to kinetic energy the gas is using to escape solid form.

Morgan Johnson - 4 years, 1 month ago

Are you saying that the coin quickly reaches thermal equilibrium with the solid? And the gas molecules are surely gaining kinetic energy because bonds are being broken, not because of the weight of the coin.

Dan Ley - 4 years, 1 month ago

@Dan Ley - I am saying that. When a gas molecule leaves the surface of the solid it takes a bit more energy than the surrounding molecules want to give up as kinetic energy. This happens even without the coin due to the temperature differential with ambient air. Thus the contribution of temperature is consistent over the whole surface an cancels out as a contributing factor to the motion of the coin. I am positing that the mass of the coin is exerting pressure over a small area (P= F/a) which is the primary source of energy for the system. The temperature of the coin in the interaction zone would contribute a negligible amount to the transition to gas.

Morgan Johnson - 4 years, 1 month ago

Quarters on Dry Ice

Image Credit: YouTube Taras Kul .

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