Up or Down? Demonstrate how the distribution of molecules in a substance determines its density. Predict, test and explain relative density by investigating the interactions of liquids and solids. For example, a suitcase jam-packed with clothes and souvenirs has a high density, while the same suitcase containing two pairs of underwear has low density. Size-wise, both suitcases look the same, but their density depends on the relationship between their mass and volume.
Mass is the amount of matter in an object. Volume is the amount of space that an object takes up in three dimensions. If we take the same volume one cubic centimetre of foam, wood and concrete, we can see that each has a different mass.
Less Dense, More Dense If something is heavy for its size, it has a high density. If an object is light for its size it has a low density. Imagine a big bowl of popcorn, compared to a big bowl of pebbles, which would feel heavier? It is easy to estimate relative densities if you keep either the volume or the mass of two objects the same. If you filled one bag with a kg of feathers and another with a kg of lead you would see that the feathers take up much more room, even though both bags have the same mass.
This because feathers are less dense, they have less mass per volume. If you made a copper cube and an aluminum cube of the same volume and placed one in each hand, you would be able to feel that the copper cube would be heavier. Copper has more mass per volume than aluminum. How can one substance have more mass per volume than another?
There are a few possibilities:. Any one or a combination of these explanations could be the reason why one substance has a higher density than another. In the case of copper and aluminum, their atoms are arranged similarly, but copper atoms are smaller and have more mass than aluminum atoms, giving it a higher density.
Materials for the demonstration 1 tea light candle Clay Clear plastic container Water Large balance Teacher preparation Use a small enough piece of clay so that you are sure that the candle weighs more than the clay.
Procedure Place a piece of clay that weighs less than a tea light candle on one end of a balance. Remove the candle from its metal container and place the candle on the other end of the balance.
Expected results Even though the candle weighs more than the clay, the candle floats and the clay sinks. Explore Have students compare the density of water, wax, and clay. Question to investigate Why does a heavier candle float and a lighter piece of clay sink?
Materials for each group 2 tea light candles in their metal containers Clay Water in cup Small balance Tape Dropper Procedure Compare the density of wax and water Roll two pieces of tape and stick them to the center of the pan at each end of the balance.
Attach each tea light candle to the tape so that each candle is in the center of the pan. Use the wick to pull one candle out of its container. Expected results The water has a greater mass than an equal volume of wax. Ask students: Which weighs more, wax or an equal volume of water? Water weighs more than an equal volume of wax. Which is more dense, wax or water?
Water is more dense. Compare the density of clay and water Make sure you have one piece of tape in the center of each pan on the balance. Fill one container with clay and place it on the tape so that it is in the center of the pan. Place an empty container on the tape at the opposite end of the balance. Slowly and carefully add water to the empty container until it is full.
Expected results The clay has a greater mass than an equal volume of water. Ask students: Which weighs more, the clay or an equal volume of water? The clay weighs more than an equal volume of water. Which is more dense, clay or water? Clay is more dense. Knowing the density of an object can help you predict if it will sink or float in water.
Instead of making an object less dense by adding bubble wrap, try changing the density of water to help an object float. Science Sparks Wild Sparks Enterprises Ltd are not liable for the actions of activity of any person who uses the information in this resource or in any of the suggested further resources.
Science Sparks assume no liability with regard to injuries or damage to property that may occur as a result of using the information and carrying out the practical activities contained in this resource or in any of the suggested further resources. These activities are designed to be carried out by children working with a parent, guardian or other appropriate adult.
The adult involved is fully responsible for ensuring that the activities are carried out safely. Your email address will not be published. Why do things float in water? Do the balls which float all have something in common? Are they hollow? Test each ball to see if your predictions are correct. Recognizing and celebrating excellence in chemistry and celebrate your achievements. Diversity in Chemistry Awards Find awards and scholarships advancing diversity in the chemical sciences.
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Students will be able to explain that the density of a substance has to do with how heavy it is compared to the size of the object. Students will also be able to explain that density is a characteristic property of a substance. Assessment does not include density or distinguishing mass and weight. Although the standard does not call for density to be used as a characteristic property to identify a substance, a basic introduction to density is included here as an optional element of a learning progression leading up to a middle school understanding of density.
Download the student activity sheet and distribute one per student when specified in the activity. The activity sheet will serve as the Evaluate component of the 5-E lesson plan. Students will record their observations, and answer questions about the activity on the activity sheet. If students dip the tiny piece of clay in the water beforehand and then put it back on the surface of the water, it should sink. Show the Animation — Density: Clay and Water.
Explain that density has to do with how heavy something is compared to its size. As you show the animation, explain that since a piece of clay weighs more than the same amount, or volume, of water, clay is more dense than water. Since clay is more dense than water, a ball of clay sinks in water, no matter how big or small the ball of clay is. Show the Animation — Density: Wood and Water.
If you compared the weight of wood and an equal amount, or volume, of water the sample of wood would weigh less than the sample of water. This means that wood is less dense than water. Since wood is less dense than water, wood floats in water, no matter how big or small the piece of wood is.
The key to floating is being light for your size.
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