Determine which possesses more mass

You can really see relative densities at work when you look at a heavy object floating and a lighter one sinking. For example, imagine putting a small piece of clay and a large, heavy wax candle in a tub of water. Sinking and floating applies to liquids too. For example, if you add vegetable oil to water, the oil floats on top of the water because the oil has a lower density than the water. The water pushes upward against the object with a force buoyancy equal to the weight of water that is displaced.

When the ball is submerged in the water, it displaces its volume in water. However, the weight of the ball is more like 55 N. A beach ball may have the same volume as a bowling ball, but it has a much smaller mass. When you a beach ball in a tub of water, it displaces the mass of water equal to its own mass—about 0. If you were to try to push the beach ball down and displace more water, the water would push back with a force greater than the weight of the beach ball.

The push of the water keeps the beach ball afloat. Buoyancy is the upward force we need from the water to stay afloat. Buoyant forces are why we feel so much lighter when we are in a swimming pool.

Our bodies are mostly water, so our density is fairly close to that of water. Because of this, an average person needs only a little bit extra buoyancy to float. A life jacket provides this extra lift. Changing Density You can change the density of a substance by heating it, cooling it, or by adding something to it. There are two possible ways to make that object float, however:.

Archimedes : Greek mathematician, physicist, engineer, inventor and astronomer c. In other words, the buoyancy is equal to the weight of the displaced fluid.

There are several possible answers for why sample B is more dense than sample A. Any one of these explanations alone, or any combination, could be the reason why Sample B is more dense than Sample A.

The American Chemical Society is dedicated to improving lives through Chemistry. Skip Navigation. Lesson 3. Engage Do a demonstration to show that cubes of the same volume but made of different metals have different masses. Question to investigate Do cubes of exactly the same size and shape, have the same mass? Materials for the demonstration Copper cube and aluminum cube of the same volume Balance Procedure Place the copper and aluminum cube on opposite sides of a simple balance.

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. This demonstration illustrates the methods for measuring the density of solids and liquids. Using a volumetric flask and an analytical balance, the density of ethanol can be determined.

Using a graduated cylinder, analytical balance, and water as the displaced liquid, the density of zinc metal can be determined. By definition, all matter has mass and occupies volume. The density of a substance is the ratio of its mass to its volume. At constant temperature and pressure, the density of a substance is constant.

Thus, density can be used to identify an unknown pure substance if a list of reference densities is available, and the experimenter can choose a convenient amount of substance to work with when measuring density. To measure the density of a sample of a substance, it is necessary to measure its mass and volume. Mass is typically measured using an analytical balance, a precise instrument that relies on the force exerted by the sample due to gravity.

The container to hold the sample also used to measure volume is weighed and tared, so only the sample mass appears on the balance display when the sample is added to the container. For liquids, this container is typically a volumetric flask, which has one marking that corresponds to a specific volume. The container is filled to the line with the liquid sample and weighed again after the empty flask has been tared.

The measured density is the ratio of the measured mass to the volume indicated on the flask. Most solid substances are irregularly shaped, which complicates volume determination. It is inaccurate, for example, to determine the volume of a powder by measuring its dimensions. Instead of directly measuring dimensions or using glassware like a volumetric flask, it is necessary to make use of a liquid displacement method to measure the volume of an irregularly shaped solid.

A graduated cylinder containing a known volume of liquid in which the solid is insoluble is tared. The solid is added to the cylinder, and the total mass is weighed again to determine the mass of the solid. Addition of the solid causes an upward displacement of the liquid, resulting in a new volume reading.

The volume of the solid is equal to the change in volume due to liquid displacement i. As for liquids, the measured density of a solid sample is the ratio of the measured mass to the measured volume. Subscription Required. Please recommend JoVE to your librarian. Density, defined as a substance's mass per unit volume, is an important physical property for characterizing a material or chemical system.

To obtain the density of a substance, its mass and volume are determined by measurement. This video will introduce the principles of density determination, the procedures for calculating the density of both solid and liquid substances, and some applications of density in scientific research. However, the volume of space occupied by the same mass is different for different substances, depending on their respective density.

For example, a ton of bricks has the same mass as a ton of feathers, but occupies considerably less volume. Density is obtained by dividing mass by volume. Mass can be measured with scales or balances, and is expressed in grams or kilograms. By convention, the volume of liquids and gases is often expressed in units of liters or milliliters, measured with glassware. The dimensions of regularly shaped solids can be measured directly with rulers or calipers, which have linear units, giving volumes in units such as cubic centimeters.

One milliliter is equivalent to one cubic centimeter. The dimensions of irregularly shaped solid samples cannot be easily measured. Instead, their volumes can be determined by submerging the solid in a liquid.

The volume of the submerged solid is equal to the volume of liquid displaced. Now that you understand the concept of density, let's take a look at two protocols for accurately determining the density of a liquid and a solid. To begin this procedure, place a clean and dry mL volumetric flask on an analytical balance. After the measurement has stabilized, tare the balance. Assume coffee has the same density as water. What is the depth of the tank if it is 0.

A trash compactor can reduce the volume of its contents to 0. Neglecting the mass of air expelled, by what factor is the density of the rubbish increased? What is the average density of the full gas can, taking into account the volume occupied by steel as well as by gasoline? What is the density of These values are parts by mass, not volume. Assume that this is a simple mixture having an average density equal to the weighted densities of its constituents.

The nucleus of an atom has a radius about 10 -5 that of the atom and contains nearly all the mass of the entire atom. The average density of your body decreases when you take a deep breath, because the density of air is substantially smaller than the average density of the body before you took the deep breath.

Skip to main content. Fluid Statics. Search for:. Density Learning Objectives By the end of this section, you will be able to: Define density.

Calculate the mass of a reservoir from its density. Compare and contrast the densities of various substances. Which weighs more, a ton of feathers or a ton of bricks? This old riddle plays with the distinction between mass and density.