Finding Evidence Without An Eyewitness

Hi, my name is Bernie Horvath, I am the author of The Home and School Science Activity Books, Volumes I and II. My goal today is to demonstrate by simple experiments that we can prove that things exist without seeing them. You just have to be looking for evidence and ask yourself some questions. Did you ever wonder how a person could be convicted of a crime when no one saw them commit the crime? Your first thought may be fingerprints, which is an excellent idea. What if the criminal was wearing gloves? Hmmm! In a science reference book, you can find this information:
  • 1. Heat makes molecules move farther apart
  • 2.  Heat makes molecules move faster
  • 3.  No one has ever seen things like a water molecule.
If no one has ever seen a water molecule, how do they know that they exist? Well, it is from something called circumstantial evidence. What is that, you ask? It is when events such as a crime or information about molecules are discovered because of what information you can observe. A person is found with $50,000 and the bank reported that $50,000 had been stolen that day. The police have the serial numbers of the bills. That is circumstantial evidence. Here is an easy experiment you can do at home. You will need some hot and cold water, 2 identical drinking glasses, a measuring cup, a watch or clock with a second hand and some food coloring. 1. Get two identical drinking glasses and place a half of cup of water in each of them. One glass should contain cold water from your faucet and the other hot water from your faucet. BE CAREFUL WITH THE HOT WATER! Kids, do this one with teacher or parental supervision. 2. Place two drops of food coloring in each glass. Do Not touch either glass. 3. Time how long it takes for each of the food colorings to spread their color throughout the glasses. You should have noticed that the food coloring spreads throughout the glass without any stirring or help or your part. Does it make sense to say that something in the water is making the food coloring spread out? A scientist would say that whatever it is that is moving to cause the food coloring to spread out are particles (molecules), even if we can’t see them. You should have also observed that the food coloring in the glass with hot water spread out sooner than the one with cold water. That is circumstantial evidence that heat makes molecules move faster. The color change to an even color throughout is also evidence of molecules spreading out evenly. To summarize what we have learned: 1. The fact that the food coloring spreads out without being touched would lead us to conclude that something is moving in the water. If we mention the word “something”, we are saying a particle, even if it is too small to see. These particles are called molecules. This circumstantial evidence also demonstrates part of the kinetic-molecular theory that heat makes molecules move faster and farther apart. 2. The fact that the food coloring spreads out faster in the hot water is circumstantial evidence that heat makes molecules move faster. We can also notice this when water is at a rolling boil. The water moves faster as it gets hotter. It also starts to evaporate which is an example of molecules moving farther apart. In fact, in a change of state from a liquid to a gas, water will increase its volume about 1600 times.

3.You can also check out the experiment of collecting some smoke and looking at it under a microscope. The particles are all moving about. This is called Browniian motion. It demonstrates that something is making these smoke particles move about. Science believes that this movement is caused by particles too small to be seen (molecules). Check out this website for a video of Einstein’s explanation of Browniian motion:  In this video, the blue dots would represent the smoke particles being moved about by the smaller particles – molecules.

Scientists have gathered a lot more circumstantial evidence that is consistent with the theory that heat makes molecules move faster and farther apart.  Every bit of that evidence leads to the fact that molecules exist even though we may not be able to see them.