## Science Experiments With Japanese Yen Coins

February 24, 2010

by: Ron Perkins

Who knew that a single coin could be used for so many classroom science activities!  You can demonstrate concepts such as surface tension, buoyancy, and even eddy currents with a single Japanese yen!

Surface Tension: Even though aluminum has a density of 2.7 gm/cm3, and the density of water is 1 g/cm3, aluminum yen coins can float on the surface of the water!

Surface tension is a physical property of water.  It is caused by cohesion, which is the attraction of like molecules.  Water molecules are made up of two hydrogen atoms and one oxygen atom.  The “stickiness” of water is caused by hydrogen bonding.  This hydrogen bonding pulls the water molecules towards one another and forms a sort of “skin” on the surface of the water.

Using a bent paper clip or a plastic fork, gently lower the flat side of the coin onto the surface of a pan or cup of water and remove the clip or fork. The coin should rest on the surface of the water. Plastic cups, glass bowls or baking dishes with clear sides will make it easy to see the effects of surface tension. The coin will actually slightly depress the surface of the water and can easily be viewed through the side of the dish or pan.

Adding more than one coin to the pan will result in a cluster of coins forming. Since each coin depresses the surface of the water, they will tend to slowly float together and form a regular, crystalline structure. (Imagine bowling balls on a stretched bed sheet – they will slowly roll towards each other to form the most stable structure.)

Adding a few drops of soap, such as dish detergent, will break up the surface tension of the water and cause the coins to sink.

Another great surface tension experiment you can conduct with your students is to have them initially predict the number of drops of water they can fit on the face of the yen.  Then, using a pipet, have students drop water, one drop at a time, onto the face of the coin.  They will be amazed at how many drops this small coin will hold.  This activity is perfect for discussing variables that could change the results of the experiment as a result of the experimenter’s manipulation (independent variables) .  Students can brainstorm reasons that some coins held more drops of water than another.  Examples include the side of the coin that is used, how worn the coin is, and how high above the coin the water is dropped from the pipet.  Controlling as many of these variables as possible, gives the most accurate results.

Buoyancy vs. Surface Tension: A charged rod will have different effects on floating objects, depending upon whether the object is floating due to surface tension or buoyancy (displaced water). A buoyant object will be attracted to a charged rod, while an object resting on the surface of the water will be repelled. Try charging a rod or piece of PVC pipe and bring it near to a floating aluminum coin – the coin will be repelled. To demonstrate a buoyant object being attracted to a charged rod, make a small boat out of aluminum foil and float it in the same pan as the coins. This boat will be attracted to a charged rod.

Eddy Currents: For this demonstration, you will need a strong magnet, such as one of Educational Innovations’ neodymium magnets. First, demonstrate that the yen coin is not magnetic, by trying to pick it up or stick it to the magnet. Next, set the coin on a flat surface, so that it balances upright on its edge. Very quickly move the magnet back and forth over the top of the coin without touching it. The rapid movement of the magnet will induce an eddy current, which creates a temporary magnetic field in the coin. The magnetic field in the coin is attracted to the moving magnet above, causing the coin to move.

There are so many uses for this small aluminum coin in every science classroom.  You can get yours at Educational Innovations for only \$7.95 for a package of 50 yen coins!

## Density Activities With The W-Tube

February 12, 2010

by: Tami O’Connor

The W-Tube is a device that was invented and developed by Ron Perkins, Chemistry and Physics high school teacher for 33 years and founder of Educational Innovations.  This amazing teaching tool was designed to have students in every grade level, kindergarten through high school, discover and gain a deeper understanding of concepts relating to density and air pressure.

In order to solve each puzzle, students need to have a basic understanding of density and air pressure.  Depending upon the grade level of your students, you may want to conduct a few experiments or demonstrations prior to having them attempt the W-Tube challenges on their own.  The following two activities do not utilize the W-Tube, however they will provide some younger students with the background knowledge necessary to successfully complete the W-Tube challenges.

This first activity is a valuable demonstration that shows that air takes up space.  Start by balling up a paper towel or tissue and affixing it to the bottom of a plastic cup using two-sided tape.  Invert the cup with the tissue inside and then push the plastic cup into a clear container of water so the cup is completely submerged.  Your students should be able to see that, although the air is somewhat compressed within the cup, the paper at the “top” of the cup remains dry.

The second activity deals more with density, or how tightly packed the molecules are in a given object.  An object’s density is determined by comparing its mass to its volume.  For example, if you have two objects of the same size, the heavier object is said to be more dense.

Pour equal amounts of corn syrup, water and vegetable oil, into 3 different but identical beakers, and, using a balance, find the mass of each liquid.  Then, gently pour the liquid with the second heaviest mass into the beaker with the liquid with the greatest mass.  Finally, add the third liquid, which has the least amount of mass, to the beaker.  The three liquids should remain neatly layered according to their density, indicating that the less dense liquid floats on the liquid that is more dense.  This activity can also be conducted using different colored water with varying amounts of sugar in each, which would change the liquid’s density.

The W-Tube Puzzle is an excellent addition for any science table and is also great to use with students working in small groups.  The apparatus (DEN-510) contains three connected tubes that form a W.  The central t-connector between the three tubes allows water and air to move through freely.  Because air and water each take up space, by capping one or more of the tubes, you can trap the air and/or water such that they are no longer able to flow freely.  This gives the student the ability to vary the amount of water and air in each individual tube.

Activity 1 – Air Pressure

Students, working in small groups, should use pipets to fill the W-Tube with colored water in order to replicate the following diagrams.  Students should check with the teacher before emptying the W-Tube and moving on to the next diagram.  By strategically placing a cap on specific tubes, one can trap water and/or air to fill the each tube at a different level.  See the diagrams below.  The challenges become increasingly more difficult as you move down the list.  If a group of students complete their challenges quickly, ask them to replicate Challenge #3 using only one cap.  It can be done, but it is more challenging!

Air Pressure Challenge #1

Air Pressure Challenge #2

Air Pressure Challenge #3

Air Pressure Challenge #4

Air Pressure Challenge #5

Air Pressure Challenge #6

Activity 2 – Density

Provide each group of students with a beaker of sugar, food coloring (red, blue, and yellow), 3 small cups, a pipet, a spoon for measuring and mixing, and a source of water. Using the W-Tube (and the caps needed), students should alter the amount of sugar in each cup of colored water to replicate the picture provided.  For example, since the diagram shows the blue water as the bottom layer, it is the denser liquid (and has the most sugar).  Encourage your students to use as few caps as possible to complete each challenge.  Students must keep the W-Tube apparatus firmly on the table at all times during the activity (no tipping except to empty between trials).  Advanced students should develop a written plan before attempting the challenge.

Density Challenge #1

Density Challenge #2

Density Challenge #3

Density Challenge #4