Density of Matter
Why a tiny steel bolt sinks but a big wooden log floats
- say in your own words what density means,
- write the density formula ρ = m/V and explain every symbol,
- use the correct units: kg/m3 and g/cm3, and convert between them,
- rearrange the formula to find mass or volume,
- read a table of densities and compare substances.
1. What does "density" mean?
Imagine two boxes of exactly the same size. You fill one with feathers and the other with sand. The box of sand is far heavier, even though both boxes take up the same space. Why? Because sand has much more matter packed into the same volume. That "amount of matter per amount of space" is what we call density.
From an earlier topic you already know that every object is made of tiny molecules. In a dense material the molecules are heavy and sit close together. In a light material the molecules are lighter or spread further apart. Density measures how crowded the matter is.
So density is not simply "how heavy something is". A whole log of wood is heavy, but it is not dense — it is just big. A small steel nut is light in your hand, but steel is very dense. Density compares mass and size together.