For class, students were asked to read Chapter 7.1 Woodstoves in How Things Work: the Physics of Everyday Life and watch the following videos.

And lastly, Doc Schuster with heat capacity and specific heat:

I started class with a lecture on woodstoves and did a few demonstrations.  I had a small candle and we talked about what was required for it to burn – oxygen, fuel (wick & wax) and watched it go out when I put a glass jar over it, depriving it of oxygen.  I also put some food coloring in a beaker of cold water and showed the students how the food coloring just sank to the bottom of the cold water. You can also drop some food coloring into some hot water and see that it mixes much faster, demonstrating convection.  Lastly, I had some magnesium ribbon left over from chemistry last year so I burned a small piece of that by placing it over a propane burner – you can see photos of it in last year’s post.  I burned the magnesium ribbon to demonstrate that burning produces light as well as heat and to show that chemical bonds require a bit of energy (activation energy) to break them.  The magnesium ribbon needed to be over a hot flame for 20 seconds or so before it started to burn.

I found a lab for specific heat online at physicslab.  The link will take you to the lab handout and you can click on a printable version.  Students measure the mass of an empty styrofoam cup and again with approximately 50ml of cold water in the cup.  The difference in the masses gives them the mass of just the water.  IMG_3682They also measure the mass of a metal cylinder and then place it in a beaker of boiling water.  After a minute or two its a safe assumption that the metal cylinder is now at the same temperature as the boiling water, roughly 100 Celsius (ours was measured to be 99.9 Celsius).  Students then put the Vernier Go Direct Temperature Probe in the cold water and set up an iPad with the Graphical Analysis app to collect temperature data for 2 minutes.  When they were ready they lifted the hot metal cylinder out of the boiling water, letting excess water drip off, or touching it lightly to a paper towel before putting it in the cold water.  Students stirred the water gently with the temperature sensor making an effort to keep it from touching the metal cylinder.  The temperature of the water rose approximately 6 degrees Celsius in just a minute or so while the temperature of the metal cylinder dropped over 70 degrees Celsius.

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Students were given the specific heat of water of 4.184 J/gC and were able to calculate the heat gained by the water,  Qwater = mwatercwaterΔTwater. We assume that the heat energy gained by the water is equal to the heat energy lost by the metal cylinder (Qwater = Qmetal) so we can use the same equation but solve for the specific heat of the metal, cmetal = Q/(mmetalΔTmetal). All the groups got specific heats very close to the expected values for the metals we were using (copper, brass and aluminum).

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Temperature of water as hot metal cylinder is placed in the cup. Graph from Graphical Analysis App using Go Direct Temperature Probe by Vernier.

I’ve done labs like this before using regular thermometers and it works just fine, but using a temperature probe just makes it a little bit easier and produces a beautiful graph of temperature as a function of time.

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