Constructing Knowledge:
While text and graphics, whether in books or online, can help kids map out processes, and acquire the language of science concepts, sometimes hands-on experiences are the foundations that concepts attach to. Here are several that I use to help students understand how their Soda Machines "make cold".
1. Heat exchange- This is the big idea that kids need to show. All matter, including air, has some heat energy. We feel differences, while nature is always seeking equilibrium..... so energy moves from more to less energetic. Cooling happens when some mechanisms are set up to assist this.... or to force a disequilibrium= refrigeration.
Evaporative Cooling:Sweat or water drops and a little fanning of skin quickly shows that cooling is happening.... depending on what you want, you can spend quite a bit of time on this physical process. The properties of water that allow for evaporative cooling are...... cool.
An experiment to show this, with practical applications, is a wet-bulb/dry bulb thermometer.(used to measure humidity)
• Simple style- demonstration or in teams,
-Record two thermometers at room temperature
-wrap one in wet gauze, rubber band to hold
- tape to table top, with bulb just over edge
- fan the air near them vigorously for a minute or two (don't hit the bulbs kids!)
- record the temperatures (wet bulb will be cooler)
- Kids hypothesize why this happens..... extend the activity any way you want.... see weather info and ideas at http://www.usatoday.com/weather/basics/wworks0.htm
One page on this site gives a nice set of definitions for measurements http://www.usatoday.com/weather/whumdef.htm
2. Convection- A natural flow of fluids (air and liquids are both fluids) based on relative density, which is affected by relative temperature.
- Buy the GEMS science unit on Convection: A Current Event
http://www.lhs.berkeley.edu/GEMS/GEM280.html
- Check out our current tank..... here's the basic idea( picture or video):
-clear container filled with water (pyrex cake dish could work ... but long is better)
- Ice water filled glass in one end, very hot water glass in other
- Use dropper to very carefully put drop of food coloring on bottom at each end
- Observe and discuss the currents that begin.... natural energy flow
3. Pressure increase and release in closed system changes temperature
see the link to purchase some wonderful and easy devices to let the kids really play with pressure/temperature relationships..... that's what real refrigeration is all about.
Air Pressure, heating, and cooling
relatively cheap (costs about $60/class set) apparatus that helps with this concept.
http://www.arborscientific.com
do a product search for product # P1-2060
"This device works with the concept of changing temperature when pressure changes. An activity that comes with the kit explains how it works. Kids pump up a plastic soda bottle that contains a liquid-crystal thermometer strip.
They see the temperature inside the bottle climb (same as what the compressor on a refer does). Then, they let the heat dissipate to the environment and come back to ambient temperature while still under pressure (radiator fins of refer do this job). Then, the kids relieve the pressure in the bottle and watch as the internal temperature drops to BELOW ambient temp."
|