Metal is colder than wood in the same room.
for grown-ups
What we actually know
No, though it really does feel that way. Leave a metal spoon and a wooden spoon in the same room and, with a thermometer, they come out at the same temperature: the temperature of the room. Metal feels colder because your hand is warmer than the room, and metal carries heat away from your skin much faster than wood does. Your skin senses that heat leaving, and it reads as cold.
The grown-up words are conduction, and thermal conductivity for how well a material does it. Metal's thermal conductivity is high; wood, plastic and foam are low (insulators). Kea names "conducting" in the round as something fancy that grown-ups say. The idea matters more than the word.
The round's test shows it the other way round. Put an ice cube on a metal pan and another on a wooden board, side by side in the same room. The one on metal melts first, because the metal carries the room's heat into the ice faster. If the metal were really colder, its ice would melt slower. (Results vary with how thick the pan and board are, and whether one is in the sun, so if yours comes out differently, that's worth talking about too.)
The round's real subject is your senses as a source. A hand is a good feeler and a poor thermometer. "I felt it" is a real where-from, and still worth checking.
Sources: Institute of Physics, IOP Spark, "Energy transferred by conduction" (the ice on metal and plastic blocks); University of Oregon physics demonstrations, "Conduction plates"; Vanderbilt Student Volunteers for Science, conduction lesson (ice on aluminium, wood and foam). Strictly, the cold you feel on first touch is set by a material's thermal effusivity, which combines its conductivity with how much heat it soaks up. Metal is high on both and wood low, so conductivity alone gives the right picture.
What kids usually bring
- "Metal feels cold when I touch it." True, and a real where-from: touch. The round asks whether a hand feels how cold a thing is, or how fast it takes your warmth.
- "Metal things are cold, like a fridge." A fridge is cold inside, whatever it's made of. What about a spoon on the table?
- "Someone told me metal is cold." A fine where-from. The round asks whether the record says the same.
- "Things in a room end up the same warmth." Exactly what the thermometers show.
- "Metal gets hot in the sun." True, and a good sign metal isn't always cold. The claim is about the same room, with no sun.
- "My hand warms things up." Yes, and metal takes your warmth fastest of all.
At dinner
Ask: "Can something feel cold but not be cold?" Then do the ice test together: an ice cube on a metal pan, another on a wooden board. Guess first which will melt first. If you have a thermometer, try it on both.
Then the one rule: say their reason back before you give yours.
The round never tells your child what to think. This card tells you what we know, so you're never caught out. If your child wants to argue with it, that is the point.
