Topic: Measurement Aim: Describe density and how it is measured. Do Now: 1. Identify the instrument and units used to measure volume of a liquid? Of a regular solid? 2. Identify the instrument and units used to measure mass. 3. Identify the instrument and units used to measure mass. HW: 1. Research and hypothesis due on Wednesday 10/3. 2. Get Lab Safety Contract signed by parent/guardian. Density • Mass per unit volume Which box has a greater density? B A • Box A has a greater density than Box B • Why? Because it has a greater mass (more matter/ molecules) • Density of water = 1 g/mL • Density = mass = m volume v Example #1: What is the density of a metal block that has a mass of 525g and the volume is 50cm3? •D = m v •D = 525 g 3 50 cm •D = 10.5 g 3 cm Example #2: The metal block was split in half. The mass of each half is 262.5g and the volume of each half is 25cm3. Calculate the density. •D = m v •D = 262.5 g 3 25 cm •D = 10.5 g 3 cm What is the block made of? Silver = 10. 5 g/cm3 What happens to the density of a block if you cut it in half? • IT DOES NOT CHANGE!!! M = 20 gm V = 10 mL Density = 20/10 = 2 gm/mL Cut the block in half M = 10 gm V = 5 mL Density = 10/5 = 2gm/mL It remains the same !!!! • Each pure substance has it’s own density no matter what size it is. •The density of water is ALWAYS 1g/cm3!!!! Example #3 • The mass of a marble is 8.8 g. It has a volume of 2 mL. What is the density? •D = m v • D = 8.8 g 2 mL • D = 4.4 g mL Why will an • FLOATS when the object float density of the or sink? object is LESS than the density of the liquid. • SINKS when the density of the object is GREATER than the density of the liquid. Less dense than water More dense than water Warm air rises bc it is less dense than cold air which sinks. Let’s summarize… 1. What is the equation for determining density? 2. What do you know about the density of different substances? 3. Identify the density of water? 4. What would happen to the density of a substance if it was cut into four pieces? 5. Why do substances float in water? 6. Why do substances sink in water? Review: 1. The units of density could be a. milliliters per gram b. milliliters c. gram d. grams per milliliter 2. What is the density of a 40gram object with a volume of 20 milliliters? a. 2 g b. 2 ml/g c. 2 g/ml d. 2 ml/g 3. A cube is 1 cm on each side and has a mass of 2 grams. Will it float? a. yes b. no c. The only way to tell is to put it in water. . 4. The density of water is a. 1 mL/g. b. 1 g/L. c. 1 g/mL. d. 1 kg/mL. 5. An object that floats in water has a density of a.less than 1 g/mL. b.equal to 1 g/mL. c.greater than 1 g/mL. d.equal to 10 g/mL. 1. Will an object with a density of 3 3.4gm/cm sink or float in a cup of water? Explain why. 2. Will an object with a density of.086gm/cm3 sink or float in a cup of water? Explain why. • http://ippex.pppl.gov/interactive/matter/den slab.html