About 140 of you are brand new since our last issue. Welcome. This is the part of your week where physics gets weird.
Now. That fan blowing on you right now? It is heating your room.
Not a typo.
Pictured: a small space heater with excellent PR. Every watt it pulls from the wall ends up as heat in the room — it just bribes you with a breeze first.
PHYSICS WORTH SHARING
Every fan in your house is a space heater with excellent PR.
A box fan pulls somewhere between 50 and 100 watts from the wall. Conservation of energy does not let a single one of those watts disappear. Some become heat immediately in the motor. The rest become moving air — which slams into walls, furniture, and you, and turns right back into thermal energy.
Electrical energy → kinetic energy → heat. Every watt, eventually. The room gets warmer.
So why does a fan feel incredible?
Because fans don't cool rooms. They cool people. Your body builds a thin blanket of warm, humid air right against your skin — a boundary layer. The fan strips it away and replaces it with drier air, which lets your sweat evaporate faster.
And evaporation is the real MVP: every gram of sweat that evaporates hauls roughly 580 calories of heat away from your skin. Your body invented phase-change cooling a few hundred thousand years before engineers put it in your refrigerator.
This is why the Department of Energy tells you to turn fans off when you leave a room. An empty room with a running fan isn't being cooled. It's being gently baked.
The 10-Second Version: A fan converts every watt it draws into heat, so it warms the room. It cools YOU by stripping the warm air layer off your skin and speeding up sweat evaporation. Fans cool people, not rooms.
Shawn's Footnote
The heating is real but small. Sixty watts into the air of a sealed bedroom would raise the temperature about 1 °C every ten minutes — but real rooms leak heat through walls and windows far faster, so in practice the fan adds a slow simmer, not a bake. Meanwhile the convective and evaporative cooling on your skin is worth several degrees of "feels-like." The trade is enormously in your favor — but only while a human is in front of it. The DOE advice stands: fans off in empty rooms.
MYSTERY MAIL
A story that arrives in your actual mailbox — real physics hidden inside a narrative. You're not studying it. You're chasing what happens next.
FREE THIS WEEK
Five physics questions that make any room lean in. If you joined in the last two weeks (hi, all 140 of you), this one's for your back-to-school folder — open September with a "wait, WHAT?"
CLASSROOM LIFESAVER
Save for the first week of your energy unit — three items, five minutes, one busted misconception.
Ask: "Does a fan cool a room?" Let them vote. (Most say yes. Delicious.)
Grab two thermometers. Wrap one bulb in a damp paper towel. Leave the other dry.
Set both in front of a fan for 3 minutes. Have them predict first: same or different?
Drop it: the wet one reads several degrees lower. That's evaporation stealing heat in real time — and they've just built a wet-bulb thermometer, the same measurement meteorologists use for heat-danger warnings.
Close: "So what is the fan actually cooling — the room, or you?"
At least one student will insist the wet thermometer is broken. That student is now paying attention.
The whole demo: two thermometers, one damp paper towel, three minutes. The wet one reads several degrees lower — that's evaporation stealing heat in real time.
“Gravity for $500, please.”
New this week — the Physics Jeopardy Review Game Bundle ($52) just launched: 16 ready-to-project games — a Concept Review AND a Math Review for every unit — 570 questions with worked answers on every slide. Review day, back-to-school diagnostics, sub plans: covered for the entire year.
PHYSICS LAUGH
What did the thermodynamicist say to the ceiling fan?
"You're not cooling anything. You're just stirring the soup."
(The soup is air. You are in the soup.)
Stay Wildly Curious,
— Lauren & Shawn
P.S.
Mystery Mail is getting closer. If a physics story showing up in your actual mailbox sounds like magic, the waitlist button above is your move.
