Students will recognize volume as an attribute of solid figures and calculate the volume of simple rectangular prisms by counting cubic units.
Show students the two containers, one filled partly with water.
Ask your class how much water they think is in the filled container. Students will likely guess using cups as a unit. Record and praise their guesses, acknowledging the units they are using.
Wonder aloud how you might measure how much “space” is inside the containers. Let them struggle with this idea as they consider using different strategies. You don’t need to solve this right now, just get them wondering and strategizing.
Now show them a rectangular prism and ask if it would be easier to measure the space in this container or the glass, again, just getting them thinking.
Come back to the idea of units. Ask them to work in groups to think of a unit that could measure space inside of objects. Give students 2 minutes to discuss this in groups.