It is not clear from the given information whether there is a control group present in the experiment. More details are needed to determine if a control group is included and what it would be.
Validity in an experiment refers to the extent to which the results accurately and fairly represent the phenomenon being studied. Validity can be affected by various factors, including the study design, sample size, measurement instruments, and controlling for confounding variables.
To determine if the average number of drops for each group is similar, one would need to examine the bar graph provided. Four reasons why the actual number of drops for each group may be similar or dissimilar could include: the size and shape of the containers used, variations in the height from which the pennies were dropped, variations in the angle at which the pennies were dropped, and variations in the force applied when dropping the pennies.
Without access to the bar graph and more information about the experiment, it is not possible to determine if the results of this experiment are "valid" or not. Validity depends on various factors such as the methodology, data collection, control of variables, and statistical analysis.
If the other side of the penny was used, it could potentially affect the results of the experiment. It would be important for all the participants to use the same "Lincoln" side of the penny while comparing data with the rest of the class to ensure consistency and eliminate any potential bias resulting from using different sides of the penny, which may have different properties or characteristics.