1. UNIT 3 Chapter 7 7.2 – Fluids and Density

2. Objectives By the end of the lesson you should be able to: Define density Relate density to the 3 states of matter Calculate density

3. Fluids List some examples of fluids….. What is a fluid?  A fluid is any form of matter that can flow  Are solids fluids? (hint: can they flow?)

4. Solid, Liquid and Gas Density Density is the mass of a given volume  It describes how closely packed together the particles are in a material  Remember – light slows down as it enters water or glass from air because the water/glass is denser (particles packed closer together) Example: think of cars on a highway. A traffic jam would be a model of high density. Free- flowing traffic on a clear highway would a model of low density.

5. Predictions….. Which is densest – solid, liquid or gas? Why?? The key is – spacing of the particles Particles in a piece of solid metal are tightly packed In water they have enough room to change position The particles in air are free to move about and have a large amount of space between them

6. Now draw! Examine the beaker at the front of the class and draw the three different states showing the particles in each state of matter (the solid, liquid and gas)

7. Remember the KMT…. Remember that according to the KMT, the particles of a substance will spread out as they gain energy when heated. Therefore, they will take up more space and so the density of the substance will decrease Most substances are denser in their solid form than their liquid form BUT is an exception…..

8. Ice Floats?? How does ice float?? If solids are denser than liquid, why do ice cubes in your drink float?? Water is an exception – when water freezes, the particles move slightly farther apart as they become fixed in position Ice is actually less dense than liquid water = floats!! This makes it possible for life in freshwater possible, ice = an insulating barrier against cold temperatures

9. Layers of Fluids Imagine oil and balsamic vinegar – which one is ‘floating’ on top? Or think of an oil spill – where is the oil? Why does this happen? Some liquids float on top of others because liquids layer in order of density The less dense liquid floats on the denser liquid if the two liquids do not mix What would happen if you put syrup and water together?

10. Layers of Fluids Layering according to density can also occur within the same substance  AIR Differences in air density contribute to weather Air that is heated near the ground has a lower density than the air around it  so it rises As warm air rises, cool air rushes in and under and we get a breeze

11. Air Air is mostly made of nitrogen and oxygen Air particles close to Earth’s surface are dense As we increase altitude = areas of lower air density occur Higher up = farther apart the air particles are which makes it harder for us to get enough oxygen in with every breath

12. Volume Volume – measured in cubic centimeters (cm 3 ) Cubic centimeter = volume of a cube that is 1cm on each side So…volume of an object = number of 1cm cubes it takes to fill that object To calculate  Volume = length x width x height

13. Displacement Displacement is the amount of space an object takes up when placed in a fluid Think of people crammed in a hot tub and one more person gets in – what happens to the water?? The amount of water you are displacing is the volume of your body that is in the water Therefore – by measuring the displacement of an object, you can measure the volume of the object

14. Measuring Density If you place an object in a less dense fluid, what will happen? What will happen if the object has the same density as the fluid? This is one way to measure density but there is a more specific way To measure density of a substance we need to know: mass and volume

15. Calculating Density If you know mass and volume – you can calculate density Density of fluids measured in g/mL Density of solids measured in g/cm 3 To calculate:  Density (D) = mass (m) volume (V)

16. Example: 1mL of glycerol has a mass of 1.26g. What is the density of glycerol? D = m V = 1.26g 1 mL The density of glycerol is 1.26g/mL

17. Your turn! Try practice problems #1-3 page 265