Density and pressure

What this chapter teaches

Density is mass divided by volume, in g/cm³ or kg/m³. Water is about 1 g/cm³, so things denser than water sink. Pressure is force divided by area, in N/m², which is called pascals. The same force on a smaller area gives a bigger pressure.

Three questions to ask

There is no one right wording. Listen for the idea.

1. Why does a huge log float when a small nail sinks?
2. How would you find the mass of a block if you know its size and what it is made of?
3. Why does a sharp knife cut better than a blunt one, if you push with the same force?

After the chapter, the learner can

• Use density = mass ÷ volume to find any one of the three
• Use pressure = force ÷ area
• Find the mass of a block from its size and density