Archimedes principal is pretty easy…if stated easy. Try this: IF YOU WEIGH 120 POUNDS, THEN THE WATER YOU DISPLACE WHEN FLOATING WILL ALSO WEIGH 120 POUNDS.
In this lab students take a 4 ounce plastic cup, place between 5 to 40 pennies in the cup, weigh it, float it, capture the overflow, measure the overflow, then make a graph and see show close together your data points plot out.
When you have students do a group lab they each need to have a job. This lab has the "masser", the volume person, the graduated cylinder person and if a 4th person a calculator.