Air Is Matter: Investigating an Invisible Gas
Students trap and release air to gather evidence that this invisible material takes up space and can move objects.
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What Can Air Do?
Air is all around us, even though we usually cannot see it. Air is matter because it takes up space and can push or move objects. You can observe moving air when you blow across a small piece of paper. The paper bends or slides because the moving air pushes it. You can also feel air from a fan on your skin. To investigate air, ask a question such as, “What happens when air is trapped?” Then make careful observations. Look for changes in an object’s shape, size, or movement. These changes can be evidence that air is present. Air is invisible, but its effects are observable. Never put plastic bags over your head or face, and use investigation materials only as your teacher directs.
Trap Air in a Bag
Open a zip-top bag and move it through the air. Close the bag tightly without squeezing out the air. The bag looks puffy because air is trapped inside and takes up space. Gently press the bag with one hand. You can feel the air push back, and the bag changes shape. Next, open one corner and slowly squeeze. You may feel air leaving the opening. Hold a light paper strip near the opening to observe the escaping air move it. Compare the bag before and after releasing the air. The filled bag is puffy, while the emptied bag is flat. Record what you see and feel. This investigation gives evidence that air is a material that can be trapped, takes up space, and can move objects.
Find Air Underwater
Air can stay trapped even when an object is placed underwater. Push a dry paper towel firmly into the bottom of a clear cup. Turn the cup upside down, keeping it straight, and slowly lower it into a bowl of water. Do not tip the cup. The water cannot fill the cup because trapped air takes up space, so the towel stays dry. Lift the cup straight out and check the towel. Next, repeat the test and gently tilt the cup underwater. Air escapes as bubbles, and water moves into the space where the air was. The towel may become wet. Observe the bubbles and the rising water. An adult or teacher should supervise the water investigation and wipe up spills right away.
Measure an Air-Filled Bag
Measurement helps you describe how much space an air-filled bag occupies. First, lay an empty zip-top bag flat on a table. Use a ruler or measuring tape to measure its length from one end to the other in inches or centimeters. Next, trap air in the bag and seal it. Place it on the table without pressing it flat. Measure its length again in the same direction and with the same tool. Start at the zero mark each time. You can also measure how high the filled bag rises above the table. Record each measurement with its unit, such as 25 centimeters. The bag’s end-to-end length may change only a little, but its thickness increases. This increased thickness is evidence that trapped air takes up three-dimensional space.
Build an Evidence-Based Claim
Scientists use observations and measurements as evidence. Begin with the question, “Does air take up space and move objects?” Make a claim that answers the question. For example, “Air takes up space and can move objects.” Then add evidence from the investigations. The sealed bag became puffy, the upside-down cup kept water out, bubbles escaped when the cup tilted, and released air moved a paper strip. Explain how the evidence supports the claim. You might write, “The bag expanded because trapped air filled space inside it. The moving paper showed that escaping air could push an object.” Record your claim, evidence, and reasoning with words and drawings. Use only observations from the investigation, not guesses. Strong explanations connect each piece of evidence clearly to the claim.
Air and Wind in Daily Life
Wind is moving air, and it affects how people live in different places. A light wind can turn a pinwheel, move a sailboat, cool people, or dry wet clothes on a line. Strong wind can bend trees, make travel difficult, and damage buildings. People respond to local wind conditions in different ways. Farmers may use windmills to pump water, and communities may use wind turbines to make electricity. Builders design sturdy roofs in places where strong winds are common. Weather reports warn people about dangerous winds so they can go indoors and stay safe. Think about your community. You might see flags blowing, leaves moving, or windsocks showing wind direction. These observable effects provide evidence that moving air can affect objects, land, transportation, work, and daily choices.