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Science Launch G5 / Week 10 / Wednesday
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Week 10 · Water on Earth

Wednesday

Investigation: The 40-bean planet
// Salty, fresh and frozen
⏱ about 15 min

Wednesday: Investigation: The 40-bean planet

Raven pours a pile of dry beans onto a plate. "Each bean is a share of Earth's water," she says.

Rocket counts out exactly 40 beans and lines them up in rows of ten.

"Here is the puzzle," Raven says. "If 2.5 percent of the water is fresh, how many of these 40 beans are fresh?"

Nova projects a small hint: one fortieth. "Try dividing 100 by 40," she says.

Rocket scribbles on scrap paper. "2.5," he says. "Wait, so just one bean?"

What you need

  • 40 dry beans, or 40 small paper squares
  • A plate and a small cup
  • A strip of paper and a ruler
  • Crayons or markers
Safety first
Beans are for counting only. Do not eat them or put them near your mouth, nose or ears.
Keep beans away from younger children and pets.
Wash your hands after handling them.

Steps

  1. Count out 40 beans. All 40 stand for all of Earth's water.
  2. Make your prediction below.
  3. Move 1 bean into the small cup. This bean stands for all of the fresh water.
  4. Look at the 39 beans left on the plate. They stand for salty water.
  5. Now draw a strip 10 centimeters long. It stands for the one fresh water bean.
  6. Color 7 centimeters white for ice and glaciers.
  7. Color almost 3 centimeters brown for groundwater.
  8. Color the tiny bit left blue for lakes and rivers.
MAKE A PREDICTION
  • Read the question.
  • Tap your answer.
Out of 40 beans, how many stand for fresh water?
Part of the modelNumber of beans or centimeters
Salty water beans
Fresh water beans
Ice and glaciers on the strip
Groundwater on the strip

One bean out of 40 is the same as 2.5 out of 100. That is Earth's fresh water.

And most of that one bean is not even liquid. It is frozen in ice and glaciers, or hidden underground.

SCALE UP THE MODEL
  • Read the question.
  • Tap your answer.
If you used 80 beans instead of 40, how many would stand for fresh water?

What one bean means

1 bean out of 40 stands for all of Earth's fresh water.

Most of that one bean is frozen or underground.

Only a tiny bit is in lakes and rivers we can see.

BEAN MODEL THINKING
  • Read the question.
  • Tap your answer.
In the bean model, what do the 39 beans on the plate stand for?
On the 10 centimeter strip, which part is the biggest?
StatementTrue or false?
One bean out of 40 is the same as 2.5 out of 100.?
Most fresh water is in lakes and rivers.?
A model can help us see numbers that are hard to imagine.?
WHY THIS EXERCISEMost fresh water is ice or groundwater.

You built a model of the whole planet's water on a plate. Tomorrow we will explore where fresh water hides.

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