Editing Screaming Pennies

{| class="wikitable" style="color:black; background-color:#ddd; margin-left: auto; float:right"
| [[Physics]] [[Chemistry]]:
| Thermal Conductivity, Sublimation
|-
| Grade Range:
| [[Elementary School]], [[Middle School]]
|-
| Format:
| [[Hands-on]]
|}

This is a good way to catch a student's curiosity as they walk by the table or booth. Be sure to prevent students from touching the dry ice!

== Materials ==

* Dry Ice
* Small Plate or Dish
* Pennies

== Safety Precautions ==

Please read the Cryogen Safety section of the [[Demonstration Safety]] page before performing this demonstration.

This demonstration requires: Safety glasses, cryogen gloves

== Demonstration ==

# Set out the plate or dish, and have a small pile of pennies in one corner of it. Keep the center clear for the dry ice. Put on the safety glasses, and keep the cryogen gloves on the table next to the dry ice.
# When a student approaches the table, put on the cryogen gloves and pick out a piece of dry ice from the container. Hold the dry ice on the plate, and ask the student to pick out a penny. Once they do, press the penny into the dry ice. The penny will start making noise!
# Set the penny on the opposite side of the plate from the others. Use one or two more pennies while explaining what is going on, and then allow the student to touch the first penny you used. It will be cold!

== Why This Works ==

When the pennies are pressed into the dry ice, there are two major things at play. The first is that the dry ice is ''Sublimating'', or going from the solid state to the gas state. We know that it is already doing this while sitting out in an open room, since the room is substantially warmer than the dry ice. The second is that pennies are made of metal, and metals are ''Conductive''. In this case, we are seeing the penny conduct heat into the dry ice much faster than the air, causing the dry ice to sublimate much faster where the penny is being pressed. This means the expanding CO<sub>2</sub> below the penny has to squeeze out around it, causing it to squeak! Once the penny has cooled down to nearly the same temperature as the dry ice, it no longer is making it sublimate faster and the squeaking stops!

== Additional Information ==

* This demonstration is often performed with other demos that require dry ice, such as the [[Tornado Box]], the [[Blood And Buffers]], and the [[Making a Comet]] demonstrations.
* This demonstration pairs well with the [[Metal and Styrofoam]] demonstration.