Cambridge Secondary (7-9). Stage 9. MCE Science. Workbook - Unit 9: Density - Question 28

Polystyrene foam is less dense than water. Grace wanted to measure the volume of a small block of foam using the displacement method. First, she added some water to a measuring cylinder and measured its volume. Then, she added a steel block and measured the new volume. She removed the steel block and added both the foam and steel blocks to the measuring cylinder. The diagrams show her results.

Explain why Grace placed a block of steel on top of the foam.