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Matter Lab 6-8 / Week 01 / Wednesday
3/6
Week 01 · Everything Is Made of Something

Wednesday

Bench Lab: Weighing air
// Matter, mass, atoms and the big list of elements
⏱ about 20 min

Wednesday: Bench Lab: Weighing Air

Rocket arrives at the Bench with two balloons, a ruler and a roll of tape. "We are going to weigh air," he says.

"With a ruler?" Raven asks. She holds it flat on one finger until it balances.

"A ruler is a balance if you hang it right," Rocket says. He blows up both balloons until they match.

Nova hovers over the ruler, her light dim so she does not distract them. "Before you let the air out," she says, "write your prediction."

Rocket scribbles: the ruler will tip toward the full balloon. Raven writes: the ruler will stay level.

"One of us is about to learn something," Raven says, and she unties the knot on the second balloon.

The air sighs out. They both lean in to watch the ruler.

Your mission

Today you will do two investigations. First, you will show that air has mass with two balloons on a balance stick.

Second, you will measure the volume of an odd shaped object with the displacement method from yesterday.

The balloon test comes from a National Weather Service lesson called Heavy Air. Two balanced balloons go out of balance when one is emptied.

  • Two balloons of the same size
  • A ruler, a yardstick or a straight stick
  • String and tape
  • A measuring cup with milliliter marks
  • Water
  • A small odd shaped object that sinks: a pebble, a metal spoon or a key
  • Your Bench Log
Safety first
Blow up the balloons gently and tie them, never with a pin nearby. Let the air out by untying, not by popping.
Keep balloons away from younger children; a loose balloon is a choking hazard.
Use only water in the measuring cup today. Nothing goes in the mouth.
Wipe up spills right away so no one slips. Wash your hands when the lab is done.
  1. Inflate the two balloons so they are the same size, and tie each one with a loose knot.
  2. Tape one balloon to each end of the ruler or stick.
  3. Tie a string around the middle of the stick. Slide the string until the stick hangs level, then tape it in place.
  4. Write your prediction in the Bench Log: if one end gets heavier, will it move up or down?
  5. Carefully untie one balloon and let the air out. Tape the empty balloon back in its place.
  6. Let the stick hang freely. Watch which end moves down, and record it.
  7. Now pour water into the measuring cup to a clear mark. Record the level in milliliters.
  8. Lower your object into the water. Record the new level, then subtract to find the object's volume.
  9. Pour the water down the sink and dry your Bench.
PREDICT BEFORE YOU LOOK
  • Read the question.
  • Tap your answer.
One balloon is full of air and one is empty. Which end of the stick will sink?
Why does the stick need to be level before you start?
Your water reads 200 milliliters, and 230 milliliters with a spoon in it. What is the spoon's volume?
InvestigationPredictionWhat I sawMeasurement
Two balloons on a stick
Water alone (milliliters)
Water with object (milliliters)
Volume of object (milliliters)

What the lab shows

The full balloon weighs more than the empty one because of the air inside it. The full end sinks because of the imbalance.

Air is made of atoms and molecules. Even though they are tiny, a balloon holds a great many of them, and together they have mass.

The water in the measuring cup rose by exactly the volume of your object. Water cannot be in the same space as the pebble.

What the lab showsTrue or false?
The full balloon end sank because air has mass.?
The empty balloon end sank.?
The water level rose by the volume of the object.?
The displacement method works for a spoon or a pebble.?
WHY THIS EXERCISEThe balloon stick and the measuring cup are your two ways of proving something is matter.
The balloon stick showed that air has ____.
The measuring cup showed the object's ____.
The full balloon end of the stick sank. What does the air inside the balloon have? Type one word.
WHY THIS EXERCISESaying it in one word fixes the idea: air is matter because it has mass.
Draw your balloon stick before and after one balloon was emptied. Draw an arrow showing which end moved down.

Excellent lab work. Tomorrow you will read the big list of every kind of atom there is: the periodic table.

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