The post Just a Pinch appeared first on Bedtime Math.

]]>*Wee ones:* There are 3 teaspoons in a tablespoon. Which is bigger, the teaspoon or the tablespoon?

*Little kids:* If you throw in a teaspoon of a super-hot chili powder and then realize you needed a tablespoon, how many more teaspoons do you need? *Bonus:* If you needed a pinch of chili powder (1/16 of a teaspoon), but you put in a dash instead (1/8), did you put in too much or too little?

*Big kids:* Mice probably like to bake with dashes and smidgens, too, to make the right size meal. If your pet mouse puts in a dash, a pinch and 2 smidgens of salt, how many pinches is that in total? *Bonus:* What fraction of a *teaspoon* is that?

Answers:

*Wee ones:* The tablespoon is bigger.

*Little kids:* 2 more teaspoons. *Bonus:* Too much – so watch out!

*Big kids:* 4 pinches. *Bonus:* 1/4 teaspoon.

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]]>The post Cave of Crystals appeared first on Bedtime Math.

]]>*Wee ones:* Which is taller, that 39-foot crystal or a 30-foot tall house?

*Little kids:* If that crystal grows 1 more foot, how long will it be? *Bonus:* This hot cave was discovered in the year 2000. How many years ago was that?

*Big kids:* The temperature of the water has been at least 122 degrees for 500,000 years (half a million). How much warmer is it when it hits its 136-degree record? *Bonus:* If that giant crystal took 390,000 years to grow, about how long did it take to grow each foot of length?

Answers:

*Wee ones:* The crystal!

*Little kids:* 40 feet. *Bonus:* 14 years.

*Big kids:* 14 degrees. *Bonus:* 10,00 years per foot.

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]]>The post Quack If You Like Ducks appeared first on Bedtime Math.

]]>*Wee ones:* If you have 6 rubber ducks, what numbers would you say to count them?

*Little kids:* If you have 9 small rubber ducks and 2 big ones, how many rubber ducks do you have? *Bonus:* If all but 3 of them can squirt, how many squirt ducks do you have?

*Big kids:* For how many years has Charlotte been collecting ducks if she started in 1996 and is still at it today? *Bonus:* How would you go about guessing the number of ducks you can see in that photo?

Answers:

*Wee ones:* 1, 2, 3, 4, 5, 6.

*Little kids:* 11 ducks. *Bonus:* 8 squirty ducks.

*Big kids:* 18 years. *Bonus:* Lots of ways to do this…for instance, you could count out 5 and then seeing how many times that area shows up, then add the ones sitting around the edge. Our best shot at actual counting came to about 114, but see what you get!

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]]>The post Make Your Own Sundial appeared first on Bedtime Math.

]]>Time to get a watch, of course!

What parent hasn’t heard the “What time is it?” question and its cousin, “How much longer?” Kids can answer their own question by making a paper plate sundial.

Our day has 24 hours–the amount of time it takes for the earth to rotate once around its axis.

The game “Dizzy Bat” used to be a field day and camp color wars highlight. Grab a bat and hold it upright. Have your child lean to place her forehead on the bat (or Sun) and spin her body around it to illustrate the Earth’s rotation. How quickly can she spin around? How many times can she spin around before she gets dizzy and falls down?

Due to the Earth’s rotation, the Sun appears to move across our sky. Ancient people used the sun’s position in the sky to tell time. It was most likely the Egyptians who realized that it is possible to measure time by the shadows created from the position of the sun. The sundial, the simplest and earliest clock used this idea to mark the hours.

**Make a Simple Sundial**

The most basic type of sundial is made from a horizontal circle and a vertical stick, called the *gnomon*.

1. Poke a hole in the center of a paper plate with a pencil.

2. Push a straw through the center of a (convex side up) paper plate.

3. Use a little glue or tape to hold the straw in place.

4. Take it outside at noon and then mark the hours.

Were the marks at regular intervals? *Older kids might notice that a circle has 360 degrees and the day has 24 hours so if the hours are marked at regular intervals, they would be at every 15 degrees.*

Will the sundial work tomorrow? How about three months from now?

**More Accurate Sundials**

You can improve the accuracy of your sundial by angling your gnomon so it is at the same angle as your latitude and pointing your gnomon to the south. The easiest way to do this is to cut out a card stock triangle with the correct angle.

*Older kids may notice that you need one angle at your latitude, one 90 degree angle, and a third angle that makes up the difference between the first two angles and the total 180 degrees needed for a triangle.
*

Because the sun’s path through the sky appears lower during winter and higher in the sprint, a perpendicular gnomon will have shifting shadows. Take a look at this interactive animation that shows why angling your gnomon creates a more accurate sundial.

You could also try to make this neat equatorial sundial.

**Measuring Time**

My daughter was pondering how we can “measure” the “length” of time when we cannot see or touch the hours. Sundials are one way we can “see” time so that we can measure it.

Sand hourglasses, water clocks, and melting candles are other ways people measured time before we had mechanical clocks.

Now that you have a sundial, try using it to tell the time. Does it work in every part of your backyard? Or does it have to be in a specific place? Use your sundial to keep track of time. How many hours have you played outside?

Is the sundial useful for precise measurements, like whether or not it is your turn for the swings or how long it takes you to run from one end of the yard to another? Would another type of early, low-tech clock work better to keep track of shorter periods of time?

While you are outside playing, consider this: Does time really go faster when you are having fun?

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]]>The post Awesome, in My Book appeared first on Bedtime Math.

]]>Librarians seem to like numbers just as much as books: in just two weeks, hundreds of librarians have set up our Crazy 8s after-school math clubs that kids like you can join for free! To start a club in your town, see below! In the meantime, let’s run some numbers on the books.

*Wee ones:* Which has more pages, a 14-page book or a 17-page book?

*Little kids:* If you take out 5 books from the library, return 2 of them, take out 3 more, then return 4, how many books do you still have at your house? *Bonus:* If the rest are due a week from today (Wednesday, April 16), when are they due?

*Big kids:* If of 200 kids’ library books, half of them have 15 pages and half have 10 pages, how many pages do they have altogether? *Bonus:* How many would 200,000 books like that have?

*The sky’s the limit:* Today in particular is National Bookmobile Day, celebrating those buses and vans that drive to neighborhoods to share books with kids. Without multiplying everything out, can you tell which bookmobile gives away more books: a bookmobile that visits 42 towns and gives away 180 books at each, or a bookmobile that visits 28 towns and gives away 250 at each?

Answers:

*Wee ones:* The 17-page book.

*Little kids:* 2 books left. *Bonus:* Wednesday, April 23.

*Big kids:* 2,500 pages. *Bonus:* 2,500,000 (2 million 5 hundred thousand), since it’s 1,000 times as many.

*The sky’s the limit:* The first bookmobile reaches more kids. The second bookmobile visits 2/3 as many towns, so it would have to reach 3/2 as many kids at each to rack up the same total. That would be 270 kids per town, but it reaches only 250 apiece.

And a big shout-out to all the librarians and teachers who’ve already ordered Crazy 8s: in just two weeks we’ve set up over 500 clubs! That’s over 8,000 kids – wow! The kit really is free, funded by royalties from the Bedtime Math books. Any kid who likes math should get to enjoy it with friends – to launch a club for your town, click here.

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