Help identifying the control

[tah]

Hypothesis: If the fabric color is lighter (white), then it will absorb 5-15% less heat than the darker colored fabrics( Yellow, black, and green) after being in sunlight for 5 hours. Teacher says hypothesis must be specific like this! Basically I will fill glass jars with water, wrap them with the colored fabric and record the temp. of water after 5 hours of sunlight. Also she says we must have a control group to serve as a comparison to the experimental group. I can't quite grasp this concept. What would the control group be and PLEASE explain why. Thanks so much!

[deleted-42343]

Check out this page about variables/controls and if you have more questions after reading it, please reply to your original post and we'll get back to you:

https://www.sciencebuddies.org/science- ... bles.shtml

[deleted-71588]

Control groups come in many forms. In your case, there are a couple of possibilities:
1) Arbitrarily declare one of your groups to be the control group and evaluate all the other groups against it
2) Introduce a control group where you don't put any fabric on the jar of water

If the independent variable that you are attempting to test is the color of the cloth, then you are going to have to use identical fabric (same material, same weave, same thread density, same thread, etc.). There are other things that you need to insure are consistent such as - How tightly you wrap the jar, whether you use anything to attach it to the jar, what the starting temperature of the jar, size of jar, shape of jar, amount of water, having a good seal, sit the jars on some identical thermal insulation material to minimize thermal condutivity, and probably more.

If you think about all of the thermodynamics involved in your experimental setup, if the fabric is dry, it will act as an insulator, so the choice of a control group without fabric may fundamentally differ from the other groups. If the fabric is wet, the there will be evaporation which will actually cool the jar. IMO: that would make it a poor control group. I personally would make the argument that using one color as the "control" (one of the "self" control types of experiments).

Your experimental design also needs to consider the other thermodymanics involved. If you start with water that is colder than ambient temperature, then there will be heat gain from convection and conductivity independent of the solar heat gain. This would be a poor experimental design because the change with respect to the effect you are attempting to measure will be a much smaller component of the total change. For example, if you have a 36.3 Kg bag of salt and you drop it in the dirt, can you measure how much dirt (by weight) is on the bag? Not easily, because the accuracy of scales that can measure 36 Kg isn't going to be able accurately measure less than a gram difference.