What does density represent

Expected results The copper cube will have a greater mass than the aluminum cube. Lead a discussion about why the copper cube has a greater mass than the aluminum cube. Ask students: How can two objects, which are exactly the same size and shape, have a different mass? Help students understand that the difference in mass must have something to do with the atoms in each cube. There are three possible explanations about the copper and aluminum atoms in the cubes that could explain the difference in mass.

Copper atoms might have more mass than aluminum atoms. Copper atoms might be smaller so more can fit in the same volume. Copper and aluminum atoms might be arranged differently so more copper atoms fit in the same size cube. Give each student an activity sheet.

Project an illustration and use the pictures of the copper and aluminum atoms to introduce the concept of density. Show students the image Aluminum and Copper Atoms Point out that the copper atoms are slightly smaller than aluminum atoms. Show animations and demonstrate how to measure volume and mass of a cube. Show the animation Cube. Volume The cubes are 2. Show students that in order to calculate the volume, you multiply the length 2.

Rounding this number to Record the volume of the cube in cubic centimeters cm 3. Mass Demonstrate how to use the balance that students will be using to measure the mass of the cube. Record the mass of the cube in grams g. Density Show students how to calculate density by dividing the mass by the volume.

Explore Have students calculate the density of eight different cubes and use the characteristic property of density to correctly identify them. Question to investigate Can you use density to identify eight cubes made of different materials?

Materials for the class Set of eight cubes of equal volume Calculator Teacher preparation Use a piece of masking tape and a permanent marker to mark the eight cubes with the letters A—H. Materials for each group Cubes marked A—H that you will share with other groups Balance that can measure in grams Calculator Procedure The volume of each cube is given in the chart.

It is Find the mass in grams of each cube using a scale or balance. Record this mass in the chart. Trade cubes with other groups until you have measured the mass of all eight cubes.

Table 1. Approximate densities for various materials. Write the name of the material in your chart for cubes A—H.

Explain Discuss how the mass, size, and arrangement of atoms and molecules affect the densities of metal, plastic, and wood Explain to students that each substance has its own density because of the atoms and molecules it is made from. Metal Project the image Metal Most common metals like aluminum, copper, and iron are more dense than plastic or wood.

The atoms that make up metals are generally heavier than the atoms in plastic and wood and they are packed closer together.

The difference in density between different metals is usually bsed on the size and the mass of the atoms but the arrangement of the atoms in most metals is mostly the same.

Plastic Project the image Plastic Most plastics are less dense than metal but can have similar density to wood. Plastics are made from individual molecules bonded together into long chains called polymers. These polymer chains are arranged and packed together to make the plastic.

One common plastic, polyethylene, is made up of many individual molecules called ethylene which bonded together to make the long polymer chains. Like most plastics, the polymers in polyethylene are made of carbon and hydrogen atoms. The carbon and hydrogen atoms are very light, which helps give plastics their relatively low density.

Plastics can have different densities because different atoms can be attached to the carbon-hydrogen chains. The density of different plastics also depends on the closeness of packing of these polymer chains.

Wood Project the image Wood Wood is made mostly from carbon, hydrogen, and oxygen atoms bonded together into a molecule called glucose. These glucose molecules are bonded together to form long chains called cellulose. Many cellulose molecules stacked together give wood its structure and density. Density is one of the fundamental physical properties of any substance.

For more facts and fundamentals, read through these examples of physical properties and examples of scientific notation. All rights reserved. Oil and vinegar being poured into a bowl as examples of density. Equal to 20 degrees C 68 F and 1 atmosphere of pressure.

Our examples below are all at NTP. Equal to 0 degrees C 32 F and 1 atmosphere of pressure. Everyday Density Examples Examples of relative density, or different densities in different substances, occur throughout everyday life. In an oil spill in the ocean, the oil rises to the top because it is less dense than water, creating an oil slick on the surface of the ocean.

A Styrofoam cup is less dense than a ceramic cup, so the Styrofoam cup will float in water and the ceramic cup will sink. Wood generally floats on water because it is less dense than water. Rocks, generally being denser than water, usually sink. This obvious example illustrates the power of science in real life. Many widely used hardwoods, such as ebony , mahogany and lignum vitae , are dense enough to sink in water, and a few rocks, such as pumice, are light enough to float.

All that matters is the relative densities of the substances. Helium balloons rise because helium is less dense than the surrounding air. The measuring cup expresses liquid volume in the standard SI units of liters and milliliters. Most American measuring cups also measure liquid in the older system of cups and ounces. Scientists who work in a laboratory must be familiar with typical laboratory glassware, often called volumetric glassware.

These may include beakers, a volumetric flask, an Erlenmeyer flask, and a graduated cylinder. Each of these containers is used in a laboratory setting to measure liquid volumes for different purposes.

Different substances have different densities, so density is often used as a method to identify a material. Comparing the densities of two materials can also predict how substances will interact. If the object has a lower density than water, it will float to the top of the water.

An object with a higher density will sink. Air has a density of approximately 1. Liquids tend to form layers when added to water. Vegetable oil approx. Water itself is a complicated and unique molecule. Recall that the three basic forms of matter are solid, liquid and gas ignore plasma for the time being.