Science Buddies: "Ask an Expert"

I am confused in my understanding of contstant variable and control when I am reviewing my daughter's science fair project. She did the color changing milk experiment to see to what is the effect of liquid dish soap on the molecules in whole milk. She used 4 drops of food coloring in a dish of whole milk. She touched the center of the milk with a clean cotton swab and then put some liquid soap on the other end of the cotton swab and touched the middle of the milk. When she used the swab with soap the food coloring moved causing swirls of color on the milk's surface where as the clean cotton swab did nothing to the food coloring, the colors stayed still. She has her independent variable = dish washing soap; dependent variable =food coloring. So my two questions are 1. Would the milk, dish, & 4 drops of food coloring be considered constant variables? 2. Also is there a control? Control defined in her science packet is the trial done without changing the original factors so does that mean the control is her trial of touching the clean cotton swab to the center of the milk?

Hello and welcome to the forum:

I searched the SB project ideas and could not find this project - could you please post a link to the experiment?

1. Yes, it seems to me that milk, dish, & food coloring are constants.
2. Yes, the control seems to be the clean swab, as there is no surface tension changing chemicals on it (hopefully )

Keith

Thank you for your reply I really appreicate it. She did not find the experiment it on the sciencebuddies website project idea list. She first found it at http://stevespanglerscience.com/experiment/00000066 and http://chemistry.about.com/od/chemsitry ... icmilk.htm