1. © Edco 2010 Exploring Science Physics Learning outcomes In this section, you will learn: – The definition of density. – How to calculate density from mass and volume. – How density is connected to floating. Density and flotation

2. © Edco 2010 Exploring Science Physics Calculating density The density of an object is found by dividing the mass by the volume of the object. The units of density are kg/m 3 or g/cm 3. This should be clear since we have divided mass by volume.

3. © Edco 2010 Exploring Science Physics Example calculation What is the density of a block of wood that has a mass of 480 g and a volume of 600cm 3 ? First, check that the units fit. g and cm³ can be used. Now the formula:

4. © Edco 2010 Exploring Science Physics Example of calculation Now put the numbers into the formula:

5. © Edco 2010 Exploring Science Physics Using the formula to find mass or volume You can use the density formula in different ways depending on the information you have.

6. © Edco 2010 Exploring Science Physics Finding mass from density and volume

7. © Edco 2010 Exploring Science Physics

8. © Edco 2010 Exploring Science Physics Finding volume from density and mass If you take the mass form of the formula and divide both sides by density you get: So, if you are told that the mass of a piece of wood is 480g and the density is 0.8g/cm 3, you can find the volume:

9. © Edco 2010 Exploring Science Physics How floating is connected to density Some objects float in liquids and some sink. This is connected to the density of the object and the density of the liquid. There is a simple fact: An object will float in a liquid if its density is less than the density of the liquid

10. © Edco 2010 Exploring Science Physics When will one liquid float on another? Density also explains why one liquid will float on another. For example, oil will float on the top of water: A liquid A will float on top of a liquid B if the density of liquid A is less than the density of liquid B. [So what can you say about the densities of oil and water?]

11. © Edco 2010 Exploring Science Physics Summary: Key points Density is the mass of one unit of volume of an object. Density is calculated by dividing mass by volume. An object will float in a liquid if the density of the object is less than the density of the liquid. This is also true of two liquids.