Aim: Describe density and how it is measured. Do Now: Topic: Measurement Aim: Describe density and how it is measured. Do Now: Identify the instrument and units used to measure volume of a liquid? Of a regular solid? 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? 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 50 cm3 D = 10.5 g cm3

Example #2: The metal block was split in half 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 25 cm3 D = 10.5 g cm3

What is the block made of? Silver = 10. 5 g/cm3

IT DOES NOT CHANGE!!! What happens to the density of a block if you cut it in half?

Cut the block in half M = 20 gm V = 10 mL M = 10 gm V = 5 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

FLOATS when the density of the object is LESS than the density of the liquid. Why will an object float or sink?

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… What is the equation for determining density? What do you know about the density of different substances? Identify the density of water? What would happen to the density of a substance if it was cut into four pieces? Why do substances float in water? Why do substances sink in water?

Review: 1. The units of density could be milliliters per gram milliliters gram grams per milliliter

2. What is the density of a 40-gram object with a volume of 20 milliliters? 2 ml/g 2 g/ml

The only way to tell is to put it in water. 3. A cube is 1 cm on each side and has a mass of 2 grams. Will it float? yes no The only way to tell is to put it in water. .

4. The density of water is 1 mL/g. 1 g/L. 1 g/mL. 1 kg/mL.

5. An object that floats in water has a density of less than 1 g/mL. equal to 1 g/mL. greater than 1 g/mL. equal to 10 g/mL.

Will an object with a density of 3 Will an object with a density of 3.4gm/cm3 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/denslab.html