I think this might work

Oh wow, I found this thing that looked pretty interesting.

It is an experiment which tests whether a brand of soap is really effective in removing the fat, or the oil. This could be done by:
1. Fill a plate (with a dent in the middle) with full cream milk.
2. Drop 4 different colours of food dye in the middle, so it forms a circle.
3. Use a cotton stick thing and dip it into the soap (so the cotton tips absorb the soap)
4. Dip the cotton tip (the tip with the soap) into one of the food dye and leave it there.
What will happen is that the milk will move, spreading out from the tip of the cotton tip, and the colour dye will move with it, allowing us to see the movement of the milk. The more the milk moves, the more effective the soap is. The less it moves, the less effective the milk will be.

The reason this happens is because when soap meets fat, it will tend to grab hold of the fat, and take it with it. This is why soap is able to remove the greese from people's hands, and remove the oil on plates, etc.
I could also try out using different brands of detergent to see which brand is better.

The independent variable would be the different brand of type of soap or detergent

The dependent variable would be how much the milk would move (thus how much fat is being removed)

The controlled variable would be keeping the same brand and type of milk, same dye, same cotton tip sticks.

This website explains the chemistry of detergent:
http://chemistry.about.com/od/howthingswork/f/detergentfaq.htm

This website explains the chemistry of soap:
http://chemistry.about.com/od/cleanerchemistry/a/how-soap-cleans.htm

I hope this works!! Ms Zhang, would this experiment be acceptable?