What makes the bathtub overflow when a person settles in for a bath? Is it weight or volume? It's the volume, but children often believe it is weight that "pushes the water out of the way." In this investigation, students confront this idea head on.

Today, students gather evidence to decide if weight or volume is the determining factor in the displacement of water.

By the end of this investigation students will understand that objects submerged in water will always change the water level, and that it is volume, not weight, that determines how much water will be moved aside.

Learning Goals

• Discover what property of a sunken object makes the water rise
• Understand that two objects cannot occupy the same space at the same time

Sequence of experiences
1. Ask the question	All Class	10 Mins
2. Explore water displacement	Small Groups	15 Mins
3. Share data	All Class	5 Mins
4. Make meaning	Discussion	15 Mins

Materials and Preparation

For the class:

• Post the investigation question in a place where all students can see it.
• Prepare two class data charts, one for weight, another for volume; examples are shown in the notebooks and in Step 3.

Have the following materials ready for a demonstration at the start of class:

• 2 150cc containers with a vertical strip of masking tape applied to the outside, each approximately half full of water
• 2 rocks or minerals, one visibly larger than the other (each must fit in 150cc container)
• 1 aluminum cube (44g)
• 1 copper cube (147g)
• 1 44g cube of plastic modeling clay (same weight as aluminum cube)
• 1 3oz cup of water
• 1 pipette
• 1 plastic fork
• 1 fine tip permanent marker
• 1 paper towel

For each tray:

• 3 150cc containers with a vertical strip of masking tape applied to the outside, each approximately half full of water
• 1 aluminum cube
• 1 copper cube
• 1 piece of plastic modeling clay weighing approximately 50g
• 1 pipette
• 1 3oz cup of water
• 1 fork
• 1 fine tip permanent marker
• 2 paper towels
• 1 digital scale