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Everyone Ever Tell You are Dense? Well, you all are… Because you all have these two properties You are made up of MATTER…which means you have mass You all have VOLUME…which means you take up space When You Combine Mass and Volume, you get… Density A measure of the amount of matter that occupies a given amount of space SPACE Amount of Matter Density Aim: How is density determined? What is Density? • Which one is more dense, a bowling ball or a soccer ball? • Even though they are both approximately the same size and shape, the bowling ball is much more dense. Density • Therefore, density depends on the mass of particles and how closely packed they are. • Density = Mass Volume Let’s put it all together… • DENSITY is the ratio of the mass of a substance to the volume of the substance UNITS: commonly expressed as grams per cubic centimeter for solids and liquids and grams per liter for gases So now you’re going to say we need more units, right? Right!!!! Units for Density = Grams per cubic centimeter g/cm3 What Do All Those Letters Mean? Quick Visual Aid Want to See An Example Question? An unknown object has a mass of 15 grams and a volume of 5 cm3. What is the density of this object? Density = Mass ÷ Volume Density = 15 grams ÷ 5 cm3 Density = 3.0 g/cm3 Your Turn!!! An unknown liquid has a volume of 6 cm3 and a mass of 6 grams. What is the density of this liquid? Density = Mass ÷ Volume Density = 6 grams ÷ 6 cm3 Density = 1.0 g/cm3 Find the Density of the Cube 8 cm Mass = 480 grams 480 g = 2 g/cm3 240 cm3 3 cm 10 cm Density Problems • Calculate the density of a rock that has a mass of 40 grams and a volume of 5 cm3. • 40g/5 cm3 = 8 g/cm3 • An unknown sample has a density of 8 g/cm3. If the mass of the sample is 16 grams, what is its volume? • 8 g/cm3 = 16g/V = 2 cm3 • An unknown sample has a density of 10 g/cm3 and a volume of 2 ml. What is the mass of the sample? • 10 = M/2 ml = 20 g Density Facts • The Density of a substance remains the same regardless of size, shape, or mass of sample!!! • Example: The density of a piece of aluminum is 2.7 g/cm3. • If you cut the Al bar in half, the density of each piece is still 2.7 g/cm3 • Even if you roll the aluminum into a sheet the density will still remain the same Density of Aluminum D = 2.7 g/cm3 D = 2.7 g/cm3 By simply cutting the bar in half, the density remains the same!!! What will change the density of an object? • Temperature • As the temperature of a substance INCREASES the density DECREASES due to the expansion of the substance Inverse Relationship Most substances EXPAND when heated and CONTRACT when cooled • Warm air rises because it is LESS dense • Cold air sinks because it is MORE dense What will change the density of an object? • PRESSURE • As pressure on a substance INCREASES the density INCREASES DIRECT RELATIONSHIP • Material DENSER than water will SINK in water • Material LESS DENSE than water will FLOAT • Materials with a density EQUAL TO water may remain at ANY LEVEL • When several objects of different densities float on water, the LEAST DENSE objects float HIGHEST. 1 g/ml Object D: 2 g/cc Object C: 1 g/cc Object B: 0.4g/cc Object A: 0.8g/cc D C B A A Mass (g) Water: B Volume (cc) C D