Air is an example of matter. Air is a mixture of gases consisting of approximately 4/5 Nitrogen and 1/5 Oxygen. Like all matter, air has weight and takes up space. It can also be compressed, unlike solids and liquids. These three properties will be studied in this investigation.
Each of the experiments is listed below separately so that it can be done during a different class session. The effect will be to build up a body of knowledge with the students concerning the properties of matter in general and air in particular.
Air has weight. Matter has three forms which are solid, liquid and gas. Air is a mixture of gases so it will have weight. We can demonstrate that air has weight by comparing a full balloon with an empty balloon.
1. In their Science Journals, the students describe the apparatus shown below. They draw a picture of it as an illustration. This apparatus is the balance when both balloons are empty.
2. The meter stick is held in position while the balloon at one end is removed and replaced by a filled balloon at the 90 cm mark.
The meter stick is allowed to come to rest. It moves down demonstrating that the filled balloon is heavier than the empty balloon because it contains air.
1. Students write in their Science Journals describing what happened when the empty balloon was replaced by the filled balloon.
2. All students in the class do the experiment. They measure carefully how far down the meter stick moved for each student. These measurements are reported in the form of a table.
1. Based on the results, they write about the different repetitions of the experiment. The meter stick does not always move down the exact same distance each time. They give reasons why the meter stick does not move down the exact same distance each time.
2. The experiment can be repeated with different balloons containing different amounts of air. They can use a small amount of air, a medium amount of air and a large amount of air. The empty balloon is used as the control. They measure how far down the end of the meter stick moves for each volume of air. The results can be presented in the form of a graph. The x-axis would be the amount of air (none, small, medium, large) and the y-axis would be how many millimeters down the meter stick moved in each case.
The Upside-Down Cup demonstrates that air takes up space. Students are challenged to devise a way to submerge a tissue in water in such a way as it does not get wet. The solution is to stuff the tissue into the bottom of a cup which is then held in the water upside-down.
1. In their Science Journals, the students make a list of all of the materials they will use in the experiment.
2. They describe their ideas of how to submerge the tissue in the water without it becoming wet.
3. The solution is to stuff the tissue in the bottom of the cup and to hold the cup upside-down under the water.
1. Students write in their Science Journals that when the tissue is stuffed into the bottom of the cup and the cup is held under water, the tissue does not get wet.
2. They record their observation that the water does not enter the upside-down cup.
1. Students write in their Science Journals that the water does not enter the upside-down cup because the air in the cup prevents the water from entering.
2. Because the water cannot enter the cup, the tissue does not come into contact with the water.
3. Students can try "pouring" some of the air out of the cup to see how much air can be poured out without wetting the tissue. Most people are accustomed to pouring water or other liquids downward because of the attraction of gravity for the liquid. Because air is much less dense than water, when it is poured it travels upward through the water in the basin.
The Cartesian Diver demonstrates that air can be compressed. It is generally credited to Rene Descartes, the French mathematician and scientist who also developed the Cartesian Coordinate System which we use for making graphs.
1. Students fill the bottle with water all the way to the top.
2. Students fill the eyedropper with water so that it just barely floats.
3. Students place the cap tightly on the bottle. The line indicates the level of the water in the dropper.
4. In their Science Journals they describe the materials as shown. They also write what they expect will happen when the bottle is squeezed. They make a list of their ideas on the board. The class discusses the postulated outcomes to see if they are reasonable.
1. They squeeze the bottle and the dropper sinks to the bottom.
2. As shown in the photograph, the line indicates that additional water has entered the dropper.
1. The students write in their Science Journals an explanation about what happened when the bottle was squeezed. They note that the pressure of the squeezing compressed the air in the dropper. This added additional water to the dropper making it heavier so it sank to the bottom of the bottle.
2. Students attempt the same experiment, this time substituting a cheap, all-plastic dropper. They repeat the discussion and they try to predict what will happen in advance. When the bottle is squeezed, the dropper does not sink, no matter how much water it has in it. This is because the plastic has a density less than water. Even when it is completely filled, the plastic itself will continue to float, unlike the glass dropper which has a density greater than that of water.