The flat paper towel was probably completely dry, the one that you rolled up may have still been slightly damp inside the roll, and the one rolled with waxed paper was probably still fairly damp all over. Rolling up the paper towel kept some parts of it from being exposed to the air, so less water could evaporate and it didn't dry out as much as the one that was completely exposed to the air. The waxed paper protected the last paper towel from the air very well, so hardly any water evaporated from that one.
Many desert plants, like cacti and other succulents (read more about them in the Teacher Tidbits section), have a waxy coating on the outside of their stems and leaves. It helps them store water and protects them from losing water in the hot sun and dry air of the desert.
Which do you think is hottest, a spot in the sun or a spot nearby that's in the shade? You'll discover the answer and learn why it's true in this experiment.
In the first part of the experiment, you found that a spot in the shade is quite a bit cooler than a spot in the sun. The thermometer in the sun may have read a temperature that was hotter than the actual temperature of the air. That's because the sun was shining on the thermometer all the time and heating it up, so the thermometer was measuring the temperature of the heat from the sun's rays instead of just the temperature of the air around it. The thermometer in the shady spot was cooler because not as much heat from the sunlight could reach it. Thermometers at weather stations are always protected from direct sunlight so they can give a correct reading of the air temperature.
You could also try this experiment again using your body instead of thermometers. First, sit or stand in the sun for about 5 or 10 minutes, or until you start to feel pretty hot. Then, move into the shade for the same amount of time. You should feel a lot cooler when the time is up. That's because when the sun shines directly onto your body, you heat up faster, because your body soaks up, or absorbs, the heat from the rays of sunlight. One way animals in the desert keep cool is to rest in the shade during the day to protect their bodies from the extra heat of the sun.
In the second part, you probably read a pretty hot temperature from the first thermometer in the bucket of sand. That's because the sand absorbed the heat from the sun shining on it all day. You probably found that the temperature deeper into the sand was cooler. That's because the sun's light couldn't reach down into the sand. The very top surface was the hottest part because the sunlight could reach it. The farther down you went, the cooler the sand got, because the light and heat coming from the sun's rays were blocked by the grains of sand at the top. Heat doesn't spread very quickly in sand, so even on a very hot sunny day, the farther down into the ground (or bucket of sand) you go, the cooler it will be! Some desert animals use this to help them stay cool. They dig down, or burrow, into the ground during the day and come out at night after the sun goes down and it starts to cool down.
To learn more about deserts and cacti, check out this Teaching Tip.