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## 1 Making measurements ### Questions The volume of a piece of wood which floats in water can be measured as shown in figure 1.8. - Write a paragraph to describe the procedure - State the volume of the wood ### 2 A stack of paper contains 500 sheets of paper. The stack has dimensions of 0.297...

## 1 Making measurements ### Questions The volume of a piece of wood which floats in water can be measured as shown in figure 1.8. - Write a paragraph to describe the procedure - State the volume of the wood ### 2 A stack of paper contains 500 sheets of paper. The stack has dimensions of 0.297 m x 21.0 cm x 50.0 mm. - What is the thickness of one sheet of paper? - What is the volume of the stack of paper in cm? ## 1.2 Density Our eyes can deceive us. When we look at an object, we can judge its volume. However, we can only guess its mass. We may guess incorrectly, because we misjudge the density. You may offer to carry someone’s bag, only to discover that it contains heavy books. A large box of chocolates may have a mass of only 200 g. The mass of an object is the quantity (amount) of matter it is made of. Mass is measured in kilograms. But density is a property of a material. It tells us how concentrated its mass is. You will learn more about the meaning of mass and how it differs from weight in chapter 3. In everyday speech, we might say that lead is heavier than wood. We mean that, given equal volumes of lead and wood, the lead is heavier. In scientific terms, the density of lead is greater than the density of wood. So we define density as shown, in words and as an equation. **Density is the mass per unit volume for a substance.** ### Key Equation $density = \frac{mass}{volume}$ ### Key Words - **mass**: The quantity of matter a body is composed of; mass causes the object to resist changes in its motion and causes it to have a gravitational attraction for other objects - **density**: The ratio of mass to volume for a substance - **weight**: The downward force of gravity that acts on an object because of its mass The symbol for density is $\rho$, the Greek letter rho. The SI unit of density is kg/m³ (kilograms per cubic metre). You may come across other units, as shown in Table 1.2. ## Table 1.1 Some units of length and volume in the SI system | Quantity | Units | |---|---| | length | metre (m) | | | 1 decimetre (dm) = 0.1 m | | | 1 centimetre (cm) = 0.01 m | | | 1 millimetre (mm) = 0.001 m | | | 1 micrometre (µm) =0.000 001 m | | | 1 kilometre (km) = 1000m | | volume | Cubic metre (m³) | | | 1 cubic centimetre (cm³) = 0.000 001 m³ | | | 1 cubic decimetre (dm³) = 0.001 m³ |