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What is floating in the air in your room?

Tiny bits of dust float in the air all the time. They are too small to see in normal light, but a flashlight beam in a dark room makes them sparkle. The filter in your heating and cooling system catches dust like this.

Goldstrike, your Wing Force guide
Goldstrike says“Grab a flashlight. Let’s find the dust your filter catches!”

⏱ About 15 minutes. 💧 A little wet (only in part 2). Grown-up helps: making the room dark.

What you need

Part 1: Dust beam

  • A flashlight (one with a narrow, bright beam works best)
  • A room you can make dark, with a grown-up
  • A pillow or a soft blanket

Part 2: Build a tiny filter

  • A paper coffee filter (or a paper towel)
  • 2 clear plastic cups
  • Tap water
  • A pinch of ground pepper and a pinch of salt
  • A rubber band

Steps

Part 1: Dust beam

  1. With a grown-up, close the curtains and turn off the lights so the room is dark.
  2. Turn on the flashlight and shine it across the room, not at anyone’s eyes.
  3. Look at the beam from the side. Kneel down so your eyes are near the beam. What do you see floating?
  4. Gently pat the pillow or shake the blanket a little, away from your face. Shine the beam over it again.
  5. Sit very still for 2 minutes and watch the beam. Do the bits fall, float or swirl?

Part 2: Build a tiny filter

  1. Stir a pinch of pepper and a pinch of salt into a cup of water. Pretend the pepper bits are dust.
  2. Put the coffee filter over the empty cup. Push the middle down a little to make a dip. A rubber band around the top holds it on.
  3. Slowly pour the peppery water into the filter.
  4. Look at the filter and the water in the cup underneath.

What you will see

In Part 1, the flashlight beam is full of tiny sparkly specks drifting around. After you pat the pillow, there are many more. In normal room light, you could not see them at all.

In Part 2, the pepper stays on top of the coffee filter. The water drips through into the cup, and it looks clear. The salt went through too, because it melted into the water and its pieces were too small to catch.

Why it works

The beam: Light travels in straight lines. When light hits a tiny speck of dust, some of it bounces off the speck and into your eyes. This bouncing is called scattering (SKAT-er-ing). In a bright room, there is so much light everywhere that you cannot notice the specks. In the dark, the only light is the beam, so every speck in it shines like a tiny star.

The filter: A filter is like a net with super tiny holes. Water fits through the holes, but the pepper bits are too big, so they get stuck. Filters catch things that are bigger than their holes.

How your house uses this

Dust is made of little bits from clothes, carpets, paper, outside dirt and even pet fur. Your heating and cooling system pulls air from your rooms through the big air grille called the return, usually on a hallway wall or ceiling. Before that air reaches the machine, it goes through an air filter.

  • The air filter works like your coffee filter. Air goes through, and much of the dust gets stuck.
  • This keeps the inside of the machine, like the fan and the cold coil, from getting coated in dust.
  • Over time, the filter fills up and turns gray. A full filter makes it harder for air to get through, like trying to drink a thick milkshake through a tiny straw.
  • That is why grown-ups change the filter on a regular schedule.

Next time a grown-up changes the filter, ask if you can look at the old one and the new one side by side. What color is each one?

See how the air moves around the whole house in The Air Trail.

Try this next

  • Room to room. Try the dust beam in different rooms. Which room has the most sparkles? Why do you think so?
  • Sunbeam spotting. On a sunny morning, look at a sunbeam coming through a window. It works just like your flashlight.
  • Filter test. Try a paper towel, a coffee filter and a piece of old cotton T-shirt as filters. Which one catches the most pepper? Which lets water through the fastest?
  • Clear the path. With a grown-up, find the big return grille on a hallway wall or ceiling. Is anything blocking it, like furniture, a laundry basket or toys? Help move your own stuff.

Share what you found

Turn the lights off and show your grown-up the dust beam. Then explain how a filter catches dust.

In which room did I see the most specks?

What did my tiny filter catch?

I shared what I found.

Keep exploring

  • Static Balloon: how static helps grab dust.
  • Inside the Machine
  • Missions: jobs you can do to help your home.
  • Hero Words: filter, return and more.
  • Back to the Kitchen Table Lab