Galaxies, Pennies and Grains of Rice

Learning is an emotional pursuit. A teacher’s most powerful ally is success. Students who can see (“feel”!) their own progress will bring up the perseverance needed to master each new concept.

However, there are times when math should just be fascinating. When we should all step back and say “Wow”.

Powers of ten have this potential. Let’s give it a look:

  1. GALAXIES.   We love the video “Powers of Ten” (   )     by Ray and Charles Eames back in 1977. It still captivates. It takes us into outer space (10^24 meters from home) and then down to the molecular level (10^ -16) . 
  2. PENNIES.     This set of 18 slides shows stacks of pennies; each slide has TEN times as many as the slide before. What does a quintillion pennies look like? Students love predicting the size of the next set. (and fantasizing about having that many pennies!)    Just for fun, we project the National Debt Clock:   Talk about big numbers…
  3. GRAINS OF RICE.  We bring a bag of rice from home, and fill a beaker (from the science teacher) with 0.4 liters of uncooked rice. We ask for estimates… how many people does it feed?  (2 – 4, depending!) How much does it weigh? (find out? almost a pound?) How many grains of rice is it? Aha!

This is where we need the kids’ help. We call it crowd sourcing. We pour a pile on each child’s desk, and have them count. To count 0.4 liters, you’ll have to give each child a pile that runs around 500 grains, so that’s a lot of counting. Encourage them to share shortcuts. (“One pinch is about 10 – you can go pretty fast then.” “I counted a pile of 100 and then made other piles about the same size,” etc.) Then they bring it back to the front of the room and pour it from their sheet of paper, back into the beaker. We record the total (Remembered or written down for us) on an Excel sheet.

One class got about 11,000, the other got 13,000 (we valued our use of time over precision!). So maybe it was around 12,000 grains of rice on 0.4 liters. Then we had the kids image they had a magic wand – a “Times Ten Wand”.

Music to work by:

We kept track of the LITER volume in a place value chart (above). We also recorded the number of grains of rice at this level. Then we projected this guessing game quiz (below) to have students guess the relative size of the next step.  This is just for fun! Have them hold up a white board or fingers for their best guess. Answers are included below each slide.  At the end, you’ll see why we chose the “music to work by” above!

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