When Jerome runs his hand across the pipes, they bang into each other. This causes

The effect of salt and water being mixed at different temperatures

Explanation:

An uncontrolled experiment is an experiment in which the independent variable is given to all the groups in the experiment. In other words, an uncontrolled experiment is an experiment without a CONTROL GROUP. Note that, a control group is the group that does not receive any experimental treatment.

Based on the given option, the experiment involving the effect of salt and water being mixed at different temperatures would be an example of uncontrolled experiment. This is because the salt and water mixture must be mixed at a particular temperature, which is the independent variable. Hence, one way or the other in this experiment, all the groups will receive the independent variable (different temperatures), making them all experimental groups.