Science Quest: Calculating Density

This year we are teaching all kinds of different science in our homeschool. For a variety of reasons, our high schoolers are all doing different courses- physics, chemistry, and earth science. Our middle schoolers is doing a history of science with a big mashup different science disciplines which makes it easy for me to include him on what others are doing. So, whenever I have the opportunity to do labs together, we will.

Defining Density

An object’s density is defined as its mass per unit volume. Another way to think about it is how tightly packed that object’s atoms are within the space it takes up. The further apart, the atoms are, the less dense the object. The opposite is also true. The more atoms there are packed together, the higher the density.

Archimedes discovered the principle of density when helping the king to solve a problem with his crown.

We observe differences in density when we see things float on water or when we mix liquids and they sort themselves out in layers.

Today we are going to calculate density by finding the mass and volume of various objects to see which is the most dense. Science Quest lessons are meant to help you, as a homeschooling parent, to do labs with your kids. Web searches often give classroom instructions, but these Science Quests are written for families doing science at home.

Skills Used in Calculating Density

The following skills are used in calculating density:

• Making a prediction
• Designing a data chart to record data
• Using a triple beam balance
• Measuring the volume of an irregular shape
• Calculating the volume of a regular geometric shape
• Keeping track of units during density calculations (and those of volume)
• Analyzing data and making conclusions about observations and calculations

Materials Needed to Find Density

For this activity you need to gather:

• Variety of household objects– make sure they are waterproof if they are irregularly shaped
• Rocks & minerals– if you are studying earth science, this is a good way to observe the differences in the density of various rocks you might be studying (like pumice!)
• Balance– or another way to measure mass
• Graduated cylinder– or another container in which to measure volume accurately.
• Ruler– to measure the dimensions of a regularly shaped object. These are the numbers that will go into the formula that matches the shape.
• Calculator– of course you can have your kids calculate the density manually, but if you don’t want to get bogged down in that, use the calculator!
• Data chart– this is an easy to chart to make on your own and it’s an important skill to be able to design a way to organize information. Have your students look at what they will need to write down and they can decide how to draw the chart to match. If it’s not perfect, that’s ok!

Form a Hypothesis

Students will also be called upon to make a hypothesis about which of their objects is the most dense and why. I like to remind students of both parts of a hypothesis with the statement, “I think _____ because _____.”

Scientists make predictions everyday and they test them as a life’s work. Your student can make predictions or educated guesses about what they are studying too.

Measuring Volume

One of the variables in the equation for density is volume. There are a few ways to measure the volume of an object depending on its shape.

• Regular shapes– You can use these formulas to determine the volume of a geometric shape.
• Irregular Shapes– Determine the volume by using a graduated cylinder. Fill the cylinder and record the volume. Add your object, read the volume again, and determine the difference between the two. The difference in milliliters is your object’s volume.
• Record– the value in your data chart to use later.

Measuring Mass

Mass is determined by using a balance to determine the number of grams. A balance is a handy tool to have in your home for many different science adventures.

• Make sure the balance reads zero– before you begin. This is true if you have a digital balance as well.
• Place the object– on the balance pan and be gentle
• Move the weights– in order to get the lines to match on the balance
• Read the value– add the rows together to get the total mass
• Record– the mass in your data chart

We thought this would be a great opportunity for a video. Below we share with your our process of measuring mass and volume. It doesn’t matter which order you collect the data in. You can have some of your kids working on the volume while others are doing the mass.

Density Calculations

Density is calculated by dividing the object’s mass by its volume. The equation looks like this:

Use the information you collected in your data chart to do the calculations. Which object has the highest density?

• Do the calculations.
• Remember your units- density is recorded in grams per cubic centimeter (g/cm³) or grams per milliliter (g/ml).
• Compare the results.
• The results may be surprising- it is interesting to look at the mass and volume between various objects to see which one made the difference.

Which Object Has the Largest Density?

The last thing to do is to write about the results. Even if it’s just a sentence or two, you can have your students write about what they observed and how the calculations turned out.

• If there were surprises, they can tell about them.
• Was their hypothesis correct?
• How did the data collected help them to find out the results?
• List anything you might do differently.

That’s it! You’ve successfully learned about and calculated the density of an object. This lab is appropriate for earth science, physical science, chemistry, and physics.

How to Include Multiple Ages

We did this lab as a family and it could easily accommodate sixth to twelfth grade. My suggestions for including everyone:

• Involve everyone– in making predictions and collecting data. Make sure there are enough materials for everyone to engage easily.
• Require a formal lab report– from your oldest students. A formal lab report means writing out all the part of a lab report
• Provide a lab sheet– for your youngest students. This way they can focus on gathering information without having to worry about making their own data chart.
• Require calculations– if students are capable. But, younger students can use the results for their own work.
• Analysis only– for the younger students. They can make predictions about the results by looking at the data they collected, even if they don’t know the final density right away.
• Discuss the results together– Make sure younger students get to talk about what they know before asking more of the older kids.

More Science from Blog, She Wrote

We love science! We’re teaching several different science disciplines this year.  Here are more posts to help you teach science in your home- a sort of mash up of various kinds.

Trail Planning Using Topographic Quadrangle Maps– This is a fun earth science activity on

Teaching Geography with Earth Science– Are you teaching earth science this year? We like to incorporate physical geography with our earth science course.

Science Quest Measuring Lung Capacity– This is a lab based on the respiratory system and makes a great stand alone study on lungs.

Science Quest How to Determine the Frequency of a Trait– This is a lab on the Hardy-Weinberg Principle and is a hands on addition to any genetics unit.

Science Quest Observing Onion Cells– The procedure for looking at a single layer of onion cells under the microscope.

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