Constants are just the things that aren't going to change. Variables are things that can change and whose changes may affect the results of the project.
For instance, when Galileo observed the lamps in one of the great halls, he noticed that all of the lamps rocked back and forth at the same rate after being lit. He thought this was odd because he knew that some had more oil in them (were heavier) than others, and he thought those would rock at a different rate.
In that case, one constant was the gravity and another was the length of the chains holding the lamps (all the lamps in the hall had the same length of chain holding them). A variable was the weight (amount of oil), and it didn't seem to affect their rocking. He learned, through experimenting, that if he added another variable (he changed the length of the chains), it affected the speed of the rocking.
For instance, when Galileo observed the lamps in one of the great halls, he noticed that all of the lamps rocked back and forth at the same rate after being lit. He thought this was odd because he knew that some had more oil in them (were heavier) than others, and he thought those would rock at a different rate.
In that case, one constant was the gravity and another was the length of the chains holding the lamps (all the lamps in the hall had the same length of chain holding them). A variable was the weight (amount of oil), and it didn't seem to affect their rocking. He learned, through experimenting, that if he added another variable (he changed the length of the chains), it affected the speed of the rocking.
