TOPIC: Measurement Aim:: What is mass and how is it measured? Do Now: Explain the difference between volume and mass. HW: Create 20 Density problems

Density Mass per unit volume

Box A has a greater density than Box B Why? Because it has a greater mass (more matter/ molecules) A B Which box has a greater density?

Density of water = 1 gm/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 of each half is 50cm 3 ?

D = m v D = 525 gm 50 cm 3 D = 10.5 gm cm 3

Example #2: The metal block was split in half. The mass of each half is 262.5g and the volume of each half is 25cm 3. Calculate the density.

D = m v D = gm 25 cm 3 D = 10.5 gm cm 3

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

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 gm. It has a volume of 2 mL. What is the density?

D = m v D = 8.8 gm 2 mL D = 4.4 gm mL

Why will an object float or sink? FLOATS when the density of the 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

slab.htmlhttp://ippex.pppl.gov/interactive/matter/den slab.html

Why does ice float in a glass of water????????

Notice the empty spaces within the ice structure, as this translates to a more open or expanded structure. The ice structure takes up more volume than the liquid water molecules, hence ice is less dense than liquid water.

Density of ice = 0.92 g/mLDensity of water = 1.0 g/mL

Warm air rises bc it is less dense than cold air which sinks.

D M V D = M V V = M D M = D x V

Example #1 M = 45gm D = 20.1 gm/mL Volume = ? D M V

V = M D V = 45 gm 20.1 gm/mL V = 2.2 mL

Will this object float or sink in water? Why? Sink Density is greater than the density of water

Topic: Measurement Aim: To practice measuring volume. Do Now: Explain why some objects float while others sink. HW: Ditto – Volume & Density (Finish Volume Activity)

Example #2 D = 3.5 gm/mL V = 1.6 mL Mass = ? D M V

M = D x V –M = 3.5 gm/mL x 1.6mL –M = 5.6 gm

Let’s summarize… 1.What is the equation for determining density? 2.What do you know about the density of different substances? 3.What is 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 40-gram 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 3.4 gm/cm 3 sink or float in a cup of water? Explain why. 2. Will an object with a density of.086 gm/cm 3 sink or float in a cup of water? Explain why.