Week 09 · Tuesday: The Thermostat (Everyday Machines)

Tuesday: Sense, Compare, Switch

Rocket wraps himself in a blanket. "The heat just turned off!"

Raven checks the thermostat. "The room reached 68. What do you notice?"

Later, the room cools down a little. Click. The heat turns on again.

Nova hums. "Hint: the box compares two numbers."

The thermostat senses how warm the room is.

It compares the room to the set point.

Room colder than the set point? The heater turns on.

Room warmer than the set point? The heater turns off.

In summer, some homes use cooling.

Room warmer than the set point? The cooling turns on.

Room cooler than the set point? The cooling turns off.

Either way, the thermostat is just a switch.

ON OR OFF?

Set point 68. Room is 65. What does the heater do?

Set point 68. Room is 70. What does the heater do?

What does the thermostat compare?

Set point 68. Room is 68. Is the room at the set point?

THE THERMOSTAT LOOP

1First

2Next

3Then

4Last

Try it

Be the thermostat! A grown-up says a room number.
Your set point is 68.
Colder than 68? Say "Heat on!"
Warmer than 68? Say "Heat off!"

Safety first

This is a talking game. Stay away from the real thermostat.
Only a grown-up touches the real buttons.

Sentence	True or false?
A thermostat compares the room to the set point.	?
The heater turns on when the room is warmer than the set point.	?
Cooling turns on when the room is warmer than the set point.	?
A thermostat is a kind of switch.	?

WHY THIS EXERCISEThe compare step is the whole job of a thermostat.

COOLING CHECK

Set point 75 for cooling. Room is 80. What happens?

Set point 75 for cooling. Room is 72. What happens?

Why did the heat click on again in the story?

What did Rocket wrap around himself?

Draw a thermostat with a set point. Draw the heater on or off.

When did you last hear the heat or cooling click on?

You figured out how a switch can think!

Tomorrow, we look closely at a real thermostat.