Science Buddies: "Ask an Expert"

In the lip balm experiment on this site, a test is recommended for the lip balm's ability to create a moisture barrier. I am confused about the variable in this test. It would seem that the appropriate procedure would be to only change the amount of one of the ingredients in each recipe. Can you help me think through this clearly?

Thank you,
Twila Dawe

Hi Twila,

I'm assuming that you're working on the project described here:

https://www.sciencebuddies.org/science- ... lm-recipes

You are correct that a common approach is to change only one variable in an experiment. And it may be possible to vary only one of the lip balm ingredients. But I think the lip balm recipes were designed so that the finished products would be practical examples.

As the experiment is deigned, Recipe A might be viewed as a control having equal parts of oil and butter. Recipes B and C test the effects of “trading” oil for butter. Recipe D tests the effects of lower wax content.

I hope this helps. Please ask again if you have more questions.

A. Norman

Thank you so much for taking the time to respond. I really want to understand, but I am not very science minded. I can see how the first recipe would be the control, but then it seems that for recipe B and C, 2 variables are changed in each. The documents on this site regarding variables seem to really emphasize only having one variable change at a time, so that feels confusing to me. Am I misunderstanding the concept of the independent variable? Thank you for any help you can offer.

Hi Twila,

You've asked a very good question and I don't think you've misunderstood the independent variable concept. It's important to control the variables in an experiment. And having a single independent variable certainly simplifies the experiment and evaluation of results.

In your project the lip balms are mixtures of ingredients. Recipes A, B and C have the same total amounts of almond oil and shea butter (18 g). To vary the amount of almond oil and keep the total constant, the shea butter must also change. For the comparison of these recipes you could define the independent variable as the oil:butter ratio. The ratios for Recipes A, B and C are 1:1, 2:0 and 0:2, respectively.

You can view the comparison of Recipes A and D as a second experiment. Beeswax is the independent variable.

I hope this helps. Please ask again if you have more questions.

A. Norman