Getting myself in hot water!

This week’s experiment was one I had never performed with a class before, so my conclusions were less foregone than other experiments I’ve done for this course. I did have a lot of background knowledge about insulation, just from everyday use and research I have done as a homeowner. I selected newspaper, aluminum foil, a china saucer and a down vest to act as insulators in my experiment. I used the first two because they are materials I have commonly seen people use to wrap things they want to keep hot. The saucer idea came because I’ve seen people put their saucers on top of their cups to keep their drinks hot when they had to leave them for a bit. Finally, I used the down vest because I know down is a good insulator for geese and humans, so I figured it would work well for hot water too. Both the newspaper and aluminum foil were folded into 8 layers. My hypothesis was that the down vest would keep the water the hottest after 30 minutes.

My results showed that after 30 minutes, my water which was initially 155º F (using my digital probe thermometer, which has a built in timer) were as follows:
Newspaper:    116º F
China saucer:  117º F
Aluminum foil: 118º F
Down vest:      121º F
So my hypothesis was supported. The range of difference in the other three tested materials was quite small, but I have confidence in the accuracy of the temperature measurement due to the use of the digital probe.

If I were to do this experiment again, it would be interesting to use some materials commonly used as household insulation. I would like to try a “lid” made of Styrofoam, some insulating expandable foam sprayed onto a cardboard circle cut to fit the top of the mugs, and some Fiberglass insulation, provided I could find a way to contain it so that I could avoid glass slivers. With these, I could do a direct comparison of the R value of each material before using it. I believe that the Fiberglass would do the best job of insulating, for the same reason that down was the best insulator: it traps air in small spaces.
The insulating expandable foam might also do quite well, I have less experience with it but it would be an interesting product to test. It could certainly be useful for “tightening” air leaks in the home, so if it performed well as an insulator in this experiment, it would be well worth considering for household use.

To address the question of whether hot dogs or spaghetti would stay hot longer or cool faster than the hot water, I believe that they would cool faster. I was having a discussion today with my seventh grade class about the effect of large bodies of water on weather, and we noted that meteorologists have observed that it takes water a long time to warm up, but it is much slower to cool off than land is. (This explains why coastal areas tend to have milder winters in general than inland regions.) I think that the same would apply to water and other solids, including hot dogs.

These experiments would not be easy to perform in my classroom due to lack of access to hot water and some reluctance to use hot plates to heat water (or hot dogs). I do believe with modifications, such as exchanging the mugs for paper carry out cups and adjusting the length of time for measurement, students would find this activity engaging, and would be able to see immediate applications to their lives.

Science inquiry on momentum 3/11/12

The question I chose to investigate is “Which pendulum will come to rest more quickly—a lighter pendulum or a heavier pendulum?” I chose this since I have investigated pendulums with fifth grade classes in the past, but this was a factor that had not been considered. My hypothesis was that the pendulum with the greater weight would have greater momentum and would continue to swing longer.

My setup originally had an error. I made each string supporting the pendulums the same length, which made the heavier pendulum longer, since I was using a larger, heavier bob. The heavier pendulum was about 4 cm. longer than the lighter one. (See the first picture.) I performed two trials with these pendulums before I realized my error and corrected the lengths of the pendulums so that the total pendulum length was equal. (See the final two pictures.)

My pendulums were suspended from pot hooks in my kitchen (see the second picture), allowing a stable point from which they could swing.

I then put each pendulum through three trials. When I had done the “error” trials, I discovered that I had to make a decision as to when I would decide when the pendulums had come to rest. I determined for the sake of the experiment that this meant that the pendulum must remain entirely still, which took more time than expected. For the lighter pendulum, the average time for the pendulum to come entirely to rest was 303.3 seconds. For the heavier, the average was 615 seconds.

I did expect the heavier pendulum to take longer to come to rest, since it would have the greater momentum since it had the greater mass, but I did not expect the pendulums to take as long as they did to come to total rest.

Overall, the experiment went well, although it was difficult getting the pendulums started and also starting the stopwatch at the same time by myself. This will be less of a problem in the classroom since the students will be working in groups.

In order to get a modified result, one that I hope would result in a shorter time for the pendulums to come to rest; I would have them drop the pendulums from a lower height. I wanted to keep consistent throughout the experiment so stayed with a similar drop height. I also wondered if longer strings, resulting in a longer period of motion would also allow the pendulums to come to rest more quickly. I will have to try that out at home to see what happens.

I may use this experiment in my class when I teach force and motion to my eighth grade in the last quarter. Thinking about ways to make it more exciting include using “Jeopardy” style trivia on the topic, which they love, while they wait for the pendulums to stop (I’ll have to think of a way to be sure someone remains the spotter!). Super long pendulums hung from the ceiling with larger masses done as a large group activity would likely spark their interest too. I would also use the “Pirate Ship” animation displayed on my class smart board as a “bell ringer” activity.  This activity can be related to familiar things such as playground swings and amusement park rides, so they can understand the principle has applications in everyday life.

This experiment helped me to understand more about momentum, and to be able to see it separated from surface friction. I want my students to understand about the air exerting friction on objects, and I can follow up with information about rocket ships and re-entry; and why heat shields are necessary.