Density. What would take up more space. A kilogram of feathers… Density! What would take up more space??? A kilogram of feathers….. or a kilogram of steel?? ROCKS - pass around OR

Another way to say it is, density is the measure of how ‘tightly packed’ a material How close the atoms or molecules are to each other NOT “heaviness” - density includes how much space an object takes up!! All substances have unique densities including liquids, solids, and gases Bread slice and compacted bread in large flask of water

“Compactness” or how ‘squeezed’ together Low density not compact Hot air balloon - Describe how a hot air balloon works. Defend your argument. High density: compact

Low pressure warmer air tends to rise and form clouds because the air is less dense, High pressure systems contain air mass that will……. SINK because a colder air is MORE dense

Balloon and liquid nitrogen http://hyperphysics.phy- astr.gsu.edu/hbase/thermo/balloon.html#c1 http://paer.rutgers.edu/pt3/movies/TVrhoandFb.mov What happens to the gasses in the balloon when it is placed in liquid nitrogen? (nitrogen condensed to -196 degrees celcius) www.dkimages.com

What would happen???? Mercury density = 13600kg/m3 (13.6g/cm3) Lead density = 11340kg/m3 (11.3g/cm3) Sinking vial - make it float

Lead floats on liquid mercury! (so does this pool ball)

ICE (that’s why it floats) Special Case: Ice vs. water….. Which is less dense? ICE (that’s why it floats) Which is why ice forms on top of lakes and floats in drinks!

Why is density important? Rocks, woods, metals, everything really MUST have its own specific density This can be used to identify things! Beans/ping pong ball; Big jug of water in a pool Wouldn’t you like to have a bunch of THIS dense material?

Archimedes and the Kings Crown: How we discovered how to measure volume of weird shaped things http://www.youtube.com/watch?v=hIYdxQuzb60 250 b.c., the Greek mathematician Archimedes - story http://3quarksdaily.blogs.com/3quarksdaily/images/2007/07/18/archimedes.jpg

Factors affecting Density Temperature Pressure Which is high temperature, which is low? Low pressure High pressure High Temp Low temp Low density High density Add several drops of red food color to each of two 250-mL Erlenmeyer flasks; fill them with warm tap water. (If tap water is not warm, heat some tap water on a hot plate to 40-45 °C.) Add several drops of blue food coloring to each of the other two 250-mL Erlenmeyer flasks; fill them with cool tap water. Predict the outcome when one flask is inverted over the other. Place a paper card on top of the vessel filled with warm water. Invert the flask making sure to hold the card in place. Stack it on top of one of the cool water flasks. Remove the card. Remain prepared to catch the flasks.   ** Visual here. Place a paper card on top of the flask filled with cool water. Invert the flask making sure to hold the card in place. Stack it on top of the other warm water flask. Remove the card. Wide mouth containers may also be used.

Factors affecting Density Dissolved solids – in liquids Concentration and substance dissolved Which is more dense salt or fresh water?

DENSITY! Note: 1 mL = 1 cm3 and 1L = 1000 cm3 d = mass = g or g Density really just compares the mass of an object to its volume. This is a ratio d = mass = g or g Mass usually expressed in grams OR kg Volume usually expressed in cm3 or liters, etc. volume mL cm3 Note: 1 mL = 1 cm3 and 1L = 1000 cm3

Density = amount of matter per unit volume Density is the ratio of mass to volume If the volume stays the same and the mass increases . . . 5g/2cm3 = 10g/2cm3 = the density will increase If the mass stays the same and the volume increases . . . 5g/2cm3 = 10g/5cm3 = The density will decrease 2.5 g/cm3 5 g/cm3 2.5 g/cm3 2.g/cm3

DETERMINING DENSITY LAB TIME Regular Shapes – mass, then determine the volume by formula EX: cubes, cylinders, spheres, cones, etc. Irregular shapes – mass, then measure displacement of a liquid (usually water) by that irregularly shaped object Use a graduated cylinder Add water to a predetermined level - record. Gently drop in the irregularly shaped object. Read the graduated cylinder – record. Subtract the first water level from the second – this is the volume LAB TIME

Algebra! formula’s best friend. Here are some simple rules. 1. For any equation/formula both sides of the = sign must stay equal. 2. Whatever you do on one side of the = sign you MUST do on the other. 3. Whatever function x + ÷-is being applied to the variable you must do the opposite to get rid of it. X is the opposite of ÷; + is the opposite of - Lets solve for the 3 variables in density.

(If you are lost in algebra) The “DMV” Triangle for Volume, Mass, and Density ÷ ÷ d X V Density = m V Volume = m d Mass = d x V Memorization will allow you to answer a few questions Understanding the rules of algebra will let you answer millions of them!

How do you predict sinking or floating? If the density is greater than the substance you put it in… It sinks If density is less than the substance… It floats! Float SINK or FLOAT In Water Float Sink Sink Sink Density WS (alcohol) Float (fuel) Float