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The case of the nasty note: the properties of milk fat will help crack this case.

"I'm coming," shouted Kara after she heard the doorbell ring. She was struggling to put on a pair of bright-yellow butterfly wings.

When she opened door, she found her friend Amy wearing a pig costume, and her friend Tim dressed as a carpenter.

"Wow! You both look great," she said. "I hear there's a best-costume contest at the party. One of you may even win."

"Thanks," replied Tim, sounding doubtful. "But you may be tough to beat."

"Yeah," agreed Amy, trying not to sound jealous. "Your wings are great. If anyone wins, it'll be you."

"Thanks," said Kara as she pranced around, pretending to flutter.

Tim looked at Amy and rolled his eyes. "We'd better get going," he said.


An hour later, the three friends arrived at the costume party.

"This is great!" said Kara.

"Sure is," said Tim.

But Amy just stood there looking very sad.

"What's wrong?" asked Kara.

"Don't mind her," said Tim. "She doesn't like her outfit."

"I feel like my costume is missing something," said Amy.

"Well you sure are the cleanest pig I've ever seen," said Kara. "You could use a little dirt."

"If you want, we can make fake dirt with pencils and sandpaper," Tim said to Amy. "I've got the tools to do it in here," he said pointing to his toolbox.

"Okay," said Amy, unsure.

"Don't worry. It'll be great," said Kara. "But before we start, I need a drink. I'm so thirsty!"


The friends made their way to a table, where bottles of water, juice, and milk had been placed.

Kara poured herself a glass of milk and took a sip.

"Ugh!" she cried, spitting out her drink.

"What's wrong?" asked Amy.

"This milk is awful. It tastes very heavy."

"That's because it's whole milk," said Tim, who was drinking the same type of milk. "Whole milk contains fat. It's mixed with water and a few other ingredients. Fat is what makes it taste heavy.

"Well, I usually drink skim milk," replied Kara.

"In skim milk, the fat's been removed," continued Tim. "It's an easy thing to do because fat and water don't really mix. The fat just sits on top."

"I know something else that won't mix with water," added Amy as she sipped some skim milk. "I learned today in science class that the material graphite doesn't mix with water. Do you think there's graphite in fat?"

"I don't think so," laughed Tim. "But there's definitely graphite in pencils. Speaking of which, we should get started on Amy's dirt."

"Do you want skim milk?" Amy asked Kara, holding up her cup.

"No thanks," said Kara. "I'll just stick to water."


When the kids found a small workspace, they removed the materials from the toolbox.

"To make fake dirt, we'll rub the pencil lead against sandpaper," said Tim. That should make a powder that looks like dirt."

"Make sure the dirt falls on the paper--and not on the table," said Amy. "I don't want to make a mess."

The kids worked for several minutes until they had enough "dirt." Kara then lifted the paper and sprinkled its contents on Amy.

"Wow, that looks ..." Kara stopped suddenly when she looked at the paper in her hands. A mysterious note on it had suddenly appeared. It read: "Kara, leave! You're not wanted here!"

"Who did this?!" Kara cried.

Tim and Amy just looked at each other confused.

"Oh, I have an idea," said Kara.

She then grabbed a napkin, two sheets of paper, one glass of skim milk, and one glass of whole milk. Next, she dipped one napkin into the skim milk and used it to write "Amy" on a sheet of paper. Then she dipped another napkin into the whole milk. She used it to write "Tim" on the second sheet. When the milk was dry, she grated a pencil over each sheet with sandpaper.

Kara then turned to the guilty friend. "You wrote the note!" she announced.

solve the mystery

Who wrote the note:


* Newspaper

* 2 napkins

* 2 plastic cups

* 2 sheets of paper

* 1/2 cup skim milk

* Pencil

* Sheet of sandpaper (60 grit)

* 1/2 cup whole milk

* Marker

Cover your desk with newspaper. Pour skim milk into one cup. Use a marker to label it "skim." Pour whole milk into the second cup. Label it "whole." Next, twist one napkin tightly. Dip it into the skim milk and use it to write "Amy" on a sheet of paper. Then, twist another napkin and dip it into the whole milk. Use it to write "Tim" on another sheet. Wait for the papers to dry. Then, grate pencil lead over each sheet with sandpaper. Grate enough powder to cover the names you wrote. Shake off the pencil powder.


For Grades K-4

* Abilities necessary to do scientific inquiry

* Characteristics of organisms

For Grades 5-8

* Abilities necessary to do scientific inquiry

* Structure and function in living systems


Language Arts--Reading fiction


ESTIMATED TIME: 25 minutes

Set a Purpose

To learn about the different amounts of fat in different types of milk.


* Pencil lead isn't really lead--it's made of graphite and clay.

* Graphite was first used to write with in 1564 in England. Because graphite is soft and brittle, it needed a holder to keep it from breaking. At first, sticks of graphite were wrapped with string, but later they were placed in a wooden holder.

Discussion Questions

* Have you ever tasted whole milk and skim milk? If so, how do they taste different? (Possible answers: Skim milk tastes lighter; whole milk tastes heavier; whole milk tastes richer.)


Discussion Questions

* Why do you think the guilty friend wrote the note to Kara? (Possible answers: He/she was jealous of Kara's costume; he/she wanted Kara to go home; he/she wanted to win the costume contest.)

RESOURCES a tour of how a pencil is made. This site has everything you ever wanted to know about milk and includes games, videos, and recipes.


* SCIENCE MYSTERY (Student Edition, pp. 4-5)

Two ingredients were needed for the message to appear: milk fat and graphite. Since there is no fat in skim milk, the fat came from Tim's whole milk. The graphite came from the pencil lead. Graphite and fat are attracted to each other because they both contain the same element:carbon. For a more scientific explanation, see the bottom of page 16 in the student edition.
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Title Annotation:science mystery
Date:Oct 1, 2004
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