All About Density! Homework: Density Worksheet due tomorrow!

Aim 4: How do we interpret and apply density to a number of problems? Jumpstart: Write down the three phases of matter and one property of each: 1. 2. 3.

Phases of matter 1. Solid A. Retains a fixed (permanent) volume and shape B. Rigid – particles are locked into place C. Most materials are densest in the solid face. * The exception is water

Phases of matter continued…. 2. Liquids A. Capable of flowing B. Both liquids and gases are fluids

i. Liquids . Takes the shape of its container but does not fill it

ii. Gases Takes the shape of its container and fills it

How much “stuff” is in the object or sample What IS Density? Density is defined as the amount of matter in a certain amount of space. The quantity of the material (matter) is its mass How much “stuff” is in the object or sample The amount of space occupied by the material is its volume The size of an object and how much room it takes up

So density is…. How tightly packed the matter is in an object or sample

So how is Density different than weight? Weight is the measure of how strong Earth’s gravitational pull is on you It changes depending on where you are

Density factors Think back, what instrument do scientists use to measure mass? An electric balance! Or a triple beam balance What unit is used? grams

What about its volume? A. Solids Objects with regular shapes of a regular measure with a ruler use the formula for volume. Volume = (length x width x height)

Volume continued B. Irregularly Shaped Objects 1) Use a graduated cylinder that is appropriate to the fluid 2) Volume units: (a) The unit for volume is the liter i) milliliter is commonly used for density measurements 3) Units: Usually expressed as mL 4) Water Displacement can be used for irregularly shaped objects. Objects volume = Final Volume – Initial Volume

Important reminder! Remember to read the bottom of the liquid’s meniscus to find the volume! Meniscus!

Finding Density Remember, Density is the ratio of an object/substance’s mass to its volume Density = mass/volume

Density Units a. Density is labeled using a compound unit. b. For solids use g/cm3 c. For liquids use g/mL Where can I find the density equation: Use Page 1 of the ESRT (Reffy!)

Two examples Example 1: A block has a mass of 200g ad a volume of 250 cm3. What is the blocks density? Was this item a regular or irregularly shaped object? Example 2: A 5g rock was dropped into a graduated cylinder that had 15 mL of water in it. When the rock sank to the bottom it, the meniscus read 25 mL. What is the rocks density?

Comparing Densities by Floatation in Water You can compare the density of objects when they are placed in water. Substances that are less dense than water float The less dense an object is, more it floats! Substances that are equal to water in density remain suspended in the water Substances that are more dense than water sink

Let’s estimate! Estimated Density: H2O ________ A ________ B ________ C ________ D ________ E ________ A B C D E (H2O)

Fluids will Separate According to Their Densities – which affects objects placed in them! 1.4 g/mL How far will the ball sink? Guess which colored liquids will the ball stop between? Or will it float in one liquid? ______________ Red Fluid: 2.4 g/mL Yellow Fluid: 1.0 g/mL Blue Fluid: 1.3 g/mL

Aim 5: How do we generalize and apply density to disciplines of Earth Science? Jumpstart: Solve the following density problems. Be sure to show all work! You have a rock with a volume of 8 cm3 and a mass of 24g. What is its density? You have another rock with a volume of 10 cm3 and a mass of 50g. What is its density? Of the two examples, which rock is the heaviest? The lightest? Explain. Of the two examples, which rock is denser? Explain.

How Does Density Relate to Earth Science? Factors affecting Density and Density in Earth Science A. Temperature As temperature of most substances increases Atoms move faster and spread apart Colder Warmer

Temperature continued…. Expansion increases the volume which decreases the density because the mass remains the same. This is an inverse/indirect relationship This is because one value is increasing and the other is decreasing (Moving in opposite directions)

Pressure Solids i. At great depths below the Earth’s surface, there is extremely high pressure from the overlying rocks. ii. Materials are compressed 1) Volume decreases 2) Density Increases iii. This is an Indirect relationship – because both values are moving in the Opposite direction

Pressure continued… b. Fluids (particularly gases like the atmosphere) i. As pressure decreases gas expands ii. This results in an increase in volume iii. Density decreases IV. This is an Indirect relationship

C. Shape and Size If the temperature of a material remains the same, the size and shape will not affect its density The mass and volume change proportionately Do the Aluminum pieces In both pictures have the same density? Why or why not?

D. Phases of Matter a. For most substances, atoms are most closely packed in the solid phase b. Most materials are densest in their solid phase c. What is unusual because it is densest as a liquid? i. As liquid water cools, it CONTRACTS to become denser until it reaches 4°Celcius (3.98°C) ii. As water cools PAST 3.98°C to 0°, it EXPANDS, becoming LESS DENSE – WOAH!

Why do we care Ms. Sklar? This factor is PIVOTAL to our environment Water’s strange behavior causes… Ice to float! Icebergs floating on the ocean Lakes freezing from the top down Expanding water Expanding water in pipes and cracks in the rocks will cause them to break apart

Okay, so why is water so unique? The reason for this unusual property is the nature of the water molecule: When water freezes, the water molecules form an ordered pattern. This open crystal structure causes the water molecule to spread out compared to the more closely packed molecules in liquid water. Liquid water Ice

Exit Ticket What happens to the molecules in most objects when you heat them up? In turn, what happens to the density? What happens when you cool down an object? What happens to its density?