UNIT 1: DENSITYAND

CONNECTIONSGranite

Density: 2.7 g/mL

BasaltDensity: 3.0 g/mL

IceDensity: 0.9 g/mL

WaterDensity: 1.0 g/mL

After Unit 1 you should be able to:

o Understand how to make observations and develop inferences in Earth Science

o Calculate density using the proper unitso Work interchangeably within the density equation to determine mass

or volume of a substanceo Understand that density describes how much matter is in a given

volume of a solid, liquid, or gaso Understand the properties of volume and masso Understand how substances in a mixture behave when they have

unique densitieso Understand that heat expands the volume of a substance and

decreases the density, and that cooling a substance decreases the volume and increases the density

o Navigate the reference tables that use density in some wayo Calculate volume and use the water displacement methodo Convert milliliters to cubic centimeterso Understand that density of a uniform substance does not change

regardless of sizeo Understand how convection currents form

Unit 1 vocabulary you should be able to use and understand:

o Observationo Inferenceo Triple Beam Balanceo Elevationo Jovian planetso Terrestrial planetso Convection currents

o Formulao Masso Volumeo Densityo Gramso Millilitero Centimetero Cubic centimetero Electronic balanceo Water displacemento Ratioo Mattero Contracto Expando Crusto Tectonic plateso Continental crusto Oceanic crusto Convergent boundary

The scientific method is driven by a balance between making accurate observations and developing reasonable inferences from those observations. This course requires you to think with a scientific mind. Being able to develop sound, evidence-based inferences from observations made in Earth Science will ensure your success.

Making Observations

Observations are made using the five senses: Sight Touch Taste Smell Hearing

Of these five, the sense of sight is the most commonly relied upon sense in Earth Science investigations.

Observations often require the use of scientific instruments to be accurate. A scientific instrument is any tool that you can use to make measurements or additional observations.

Examples: hand lens, electronic balance, triple-beam balance, graduated cylinder

Making Inferences

An inference is an educated guess or conclusion derived from one or a series of observations

For example: A student discovers a very large boulder in upstate New York that does not match local bedrock in the area. An inference could be that the boulder was transported by glaciers. The student observed the differences in bedrock, but did not see glaciers transport the rock, however there is supporting evidence for glaciers covering the area.

Density is a property of matter that is the ratio of mass to volume of a substance. Understanding how density impacts the behavior of interacting substances is critical in Earth Science.

The Equation in the Earth Science Reference Tables

Density = mass/volume

Before we get into the equation as a whole, let’s consider the components:

mass and volume

What is mass?

Mass is the measure of a substance’s inertia, or resistance to movement. It is very similar to weight but is not the same.

Object with a high mass: an anvil, containing iron

Object with a low mass: a feather

What is volume?

Volume is the amount of space an object takes up.

Container with a large volume: water tower

Container with a low volume: water bottle

How do you find an object’s mass?

Place the object on an electronic balance or triple beam balance

A triple beam balance requires you to find the sum of the mass of all three bars

How can you determine an object’s volume?

If the object is a regular shape, like a rectangular prism, the volume can be determined mathematically by performing the following calculation (length x width x height)

When performing such a calculation, centimeters are used. When multiplied (#cm x #cm x #cm), the appropriate units are cm3.

How can you determine an object’s volume?

The second method is water displacement. Measure the preexisting amount of water in a container, then gently place the sample in the water. Record the difference between the new measurement and old measurement. This value is the volume of the sample in milliliters (mL).

1 mL is equal to 1 cm3, so these units may be used interchangeably, although milliliters are commonly used for liquids or irregular samples.

Before finally diving into density, let’s consider our earlier examples for understanding mass.

Which is heavier, a pound of iron from the anvil, or a pound of feathers?

A pound of which material would take up the most volume?

Let’s look back at the equation:

Density = mass/volume

Density is simply the ratio of the amount of mass (matter) inside the space of an object

So in our feathers and anvil example, we can say that the feathers are much less dense than the iron from the anvil.

Sample Problem:

An Earth Science student is trying to determine the density of a sample of basalt she discovered in the field. The sample has a mass of 60 grams and a volume of 20 mL.

What is the density of the sample?

Density = mass/volumeSolution: ___________ g/mL

What if an object is cut in half? Does the density change?

A student has a wooden block that has a mass of 36 grams and a volume of 48 cm3. The density is 0.75 g/cm3

After cutting the block in half, the mass is now 18 grams, and the volume is 24 cm3. The density is 0.75 g/cm3

Density remains the same in the same material, no matter the sample size.

How can the density of a substance change?

Density will decrease if you increase the volume of an object (expansion).

Most materials decrease in density by increasing in volume during heating.

If the material cools, it will contract and become more dense.

What do less dense materials tend to do when mixed with more dense materials?

Less dense materials rise!

More dense materials sink!

In liquids and gases, this results in the formation of convection currents, a transference of energy upward due to differences in density.

Convection commonly takes place in the atmosphere and in a layer of the Earth known as the asthenosphere.

Things to know about density in Earth Science:

1. The Earth is layered based on density, with more dense materials in the core, pulled there by gravity

2. Planets closest to the Sun (Terrestrial: Mercury, Venus, Earth, Mars) are more dense than ones farther away (Jovian: Jupiter, Saturn, Neptune, Uranus)

3. Warm air will expand and become less dense, and rise

More things to know about density in Earth Science:

4. Cool air will contract and become more dense, and sink

5. Earth’s crust is made up of plates of varying densities. More dense plates (oceanic crust, made of basalt) plunge below thicker, but less dense plates (continental crust, made of granite) at convergent boundaries.

Relevant Reference Tables for Density