A control group is an experiment where the independent variable is at its normal or natural value. In our sunscreen lotion experiment, the control group would include at least one experiment where we don't use any sunscreen lotion at all. We can use the UV reading we get from this experiment as a comparison for the other trials.

Here are some steps to design your experiment:

• Identify and describe the independent, dependent, and control variables.
• Make a list of all the steps for your experiment. Be very specific and thorough, and include everything you need.
• Decide how you will measure the changes in the independent and dependent variables.
• Think about how you will keep the control variables the same. For example, if temperature and lighting are control variables, you could do the experiment in a room with air conditioning, blackout curtains, and indoor lighting.
• Decide how many times you will repeat the experiment to get accurate results.
• Consider any safety issues and procedures that you need to follow during the experiment.