# Ceiling fan arithmetic

Summer has arrived in Minnesota, and that means we alternate between warm days where we open the windows and run the ceiling fan, and hot days where we close everything up and run the air conditioning (a luxury, btw, that our 1928-built home only got about five years back).

Not our ceiling fan.
Image credit: Brian Snelson (CC-BY 2.0)

Tabitha is naturally curious about how the ceiling fan works. In case you don’t have experience with them, or yours works differently from ours, here are the basics: There is a switch on the wall—just like a light switch—that powers the fan. Then there is a chain hanging from the fan itself that affects the speed. There are four settings controlled by the chain—High, Medium, Low, and Off.

By the time this conversation takes place, Tabitha and I have already explored a variety of ceiling fan questions, such as If the fan is off, should you pull the chain to turn it on, or head over to the light switch? and How many times can I pull the chain before my parents tell me to stop playing with the fan?

On this day, I ask Tabitha to flip the wall switch to turn on the fan, which she does. She then starts to stand up on the couch to reach the chain. I ask why.

Tabitha (9 years old): I want to see if it’s on high.

Me: But how will you know? If you pull the chain it will slow down, but that’s what it always does. So how will you know whether it was on high to begin with?

T: Well, it doesn’t always slow down, otherwise how would it ever be on high?

## So What Do We Learn?

There is some very deep math going on here.

Tabitha and I are playing with properties of modular arithmetic, but she (and you) don’t need to know the specifics. Things that go in cycles are all examples of this kind of math.

The classic example is time. You could say that later times have bigger numbers. 4 is later than 3; 12 is later than 9. This is just like my claim that every pull of the chain slows down the fan. Both of these claims are only sort of true. Three in the afternoon is later than 11 in the morning, despite having a smaller number. If the fan is on low and you pull the chain twice, it’ll be on high.

People study these things in great depth in the field of Modern Algebra, and the ideas are useful in all sorts of places.

## Starting the Conversation

Play with a ceiling fan. Talk about staying up all night. Notice together that weird things happen when the fan is in the off position, and at midnight and noon. Wonder aloud whether 12 o’clock is like zero (and if not, what is?)

Play around with basic facts in this ceiling fan environment. If it’s on high, how many pulls to turn it off? If it’s on low, how many to get it to medium? I just pulled the chain three times and now it’s on low—where was it before? Etc. Challenge the child; have the child challenge you.

Stay cool!

# The Summer of Math

Hey parents! Listen closely. Do you hear that? It’s the sound of school letting out for the summer!

You’ve got your summer camps planned, your squirt guns at the ready, and you’re all set to hit the library as many times as needed to keep your kids reading all summer long.

Now you need a plan to keep their math minds active.

At Talking Math with Your Kids, we’ve got you covered.

Announcing The Summer of Math.

A small sample of the fun to be had this summer!

Here’s how it works. You can head over to the Talking Math with Your Kids store, pay for a subscription to The Summer of Math, and all summer long we’ll ship you awesome, fun stuff that will keep you and your 5—10 year old busy playing and talking math.

You’ll color, count, make patterns, designs and shapes. You’ll read together, draw, and challenge yourselves. You’ll notice. You’ll wonder. You’ll play. And when school starts back up in the fall, your kids will remember this as the best, mathiest summer ever.

The details

Each month June—September, we’ll ship you a box that contains a bunch of great stuff—at least one book, at least one related set of mathy things to play with, and at least one special surprise. For example, in June you’ll get one beautiful math coloring book, one terrific activity book, all the supplies you need for both of these, a set of spiraling pentagons (so you can make your own awesome designs like those in the coloring book), and a little something extra we cannot yet divulge.

Plus a newsletter where we’ll share additional ideas, questions, cool math stuff we’ve been doing, and reports you send us of the mathy fun you’ve had this summer.

We’ll ship the first week of each month. One week before we ship it out, we’ll send you an email letting you know exactly what’s coming your way (except for the surprise—that’s always a surprise!) You can let us know if you need to add, delete, or swap anything out. We can easily credit you for things you already have (but it’s not likely you’ll already have much of what we’ve got planned), or substitute something new and awesome for it.

We’ll have a Facebook page where we’ll share our mathy adventures and encourage you to share yours.

What are you waiting for? Click on through and join us for The Summer of Math!

# Talking Math with Your Kids update

As spring approaches, it’s time to update readers on what’s going on behind the scenes at Talking Math with Your Kids.

# The blog

The pace of posting has slowed way down in recent months. Rest assured that we’re still talking math around the house, and that my dedication to helping others do the same remains strong. I have lots to write, but not much time to write it because…

# Math On-A-Stick

Two years ago, I began to wonder how to expand the work of this blog beyond the parents who have the time, technology, and inclination to read blogs.

One year ago, I pitched an idea for this to the Minnesota State Fair.

And last summer we inaugurated what is now an annual event: Math On-A-Stick. Planning is under way for year two, with help from the Minnesota Council of Teachers of Mathematics, The Math Forum, the National Council of Teachers of Mathematics, the Minnesota State Fair, and the Minnesota State Fair Foundation.

The number one question at the Fair was Where can we buy the turtles?

At the time, the answer was “Nowhere”. We had asked permission from their designers, Jos Leys and Kevin Lee, only to cut them for Math On-A-Stick. Soon afterwards, I got permission from Jos to make and sell these turtles. I also got permission from Kevin who adapted Jos’s design for laser cutting using his own software (which is a ton of fun, and which you can buy from him) Tesselmaniac.

# The store

The Talking Math with Your Kids Store, at talkingmathwithkids.squarespace.com, opened late last fall with tiling turtles as the main offering. It is now stocked with a number of things to support parents and children in math activities and conversations—Pattern Machines, Tiling Turtles, Spiraling Pentagons, a gorgeous coloring book, and more on the way soon.

Click on through and have a look if you haven’t done so yet.

# A book

I recently submitted the final manuscript for Which One Doesn’t Belong? A Better Shapes Book. There will be both a home/student edition, and a companion guide. It is being published by Stenhouse this summer.

# More

The big ideas continue to flow, and further collaborations are in the works. Keep an eye on this space. In the meantime, you can expect a few new posts in the coming weeks as my attention shifts from book-writing mode.

And don’t forget to follow the fun on Twitter at the #tmwyk hashtag, where people share young children’s beautiful ideas and questions on a daily basis.