This activity stands alone as an investigation of two methods for finding the volume of a rectangular prism. The first way is to multiply the dimensions. The second is through water displacement. This activity also works well as part of an investigation of density. It teaches the skills necessary to find the volume of an irregularly shaped object which, when combined with the mass, can be used to find the density of the object. I have separate activities using this technique to investigate density and displacement.
For this activity you will need four different rectangular prisms. They will need to be able to fit into a plastic cup. You will need plastic bowls big enough to catch water overflowing from the cups, and you will need graduated cylinders to measure the overflow.
I have included some photos of the set-up, and there are photos in the activity itself. The photos are in color, but they photocopy well in black and white. I have also included some notes for the unit. These were in my files, but do not pertain directly to the activity. Feel free to ignore them, or have a look.
You will find that the water displacement method is reasonably accurate for larger items. Because it is difficult to get the water level in the cup full to the point of overflowing, the experimental error is a greater proportion of smaller items. In addition, if just a little water overflows the cup, it is nearly impossible to then move the cup to get the water in the bowl without spilling much more.
One was to find the displacement of small items is to fill a graduated cylinder to a round value and then place the object into the cylinder. Then see how the water level has risen and find the difference. There is a question on the activity that leave room for students to come up with this idea on their own. If they do not, you could share it with them.
I have listed a small beaker as one of the supplies. It is easiest to pour the water from the bowl into something with a pouring spout, like a beaker, to aid in getting the water into the graduated cylinder without spilling any.
If you have time, an excellent extension for this activity, and one that is enjoyed by the students, is to have them find irregularly shaped objects from around the room of which they can find the volume. The last page of the activity sheets has room for this information.