Why do lower density things float

In these activities, students will learn about mass , volume and density and their relationship to each other by conducting investigations into buoyancy : floating and sinking objects used in their everyday lives. Dense, Denser, Densest! 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.

Density, Sinking and Floating Why do some things float, while others sink? You might expect heavier objects to sink and lighter ones to float, but sometimes the opposite is true. The relative densities of an object and the liquid it is placed in determine whether that object will sink or float.

You can really see relative densities at work when you look at a heavy object floating and a lighter one sinking. Awards Recognizing and celebrating excellence in chemistry and celebrate your achievements. Funding Funding to support the advancement of the chemical sciences through research projects. Lesson 2. Inquiry in Action. Lesson Overview for Teachers View the video below to see what you and your students will do in this lesson. Objective 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.

Key Concepts Density is a measure of how heavy something is compared to its size. If an object is more dense than water it will sink when placed in water, and if it is less dense than water it will float. Summary Students are introduced to the concept of density and that density has to do with how heavy something is relative to its size. Students are also introduced to the idea that whether a substance sinks or floats in water is a characteristic property of that substance and does not depend on the amount of the substance.

Students also learn that if an object is more dense than water it will sink when placed in water, and if it is less dense than water it will float. Evaluation Download the student activity sheet and distribute one per student when specified in the activity. Safety Make sure you and your students wear properly fitting safety glasses or goggles. Clean-up and Disposal Remind students to wash their hands after completing the activity.

All common household or classroom materials can be saved or disposed of in the usual manner. Materials Clay 1 ball for each group Clear plastic container of water Popsicle sticks 20 Rubber band. Engage 1. As a demonstration, place a clay ball in water to show that clay sinks. Materials for the demonstration: Ball of clay Clear plastic container of water Procedure Hold up a ball of clay about the size of a ping pong ball and ask students if they think it will sink or float in water.

Place the clay in the water. Expected result The clay ball will sink. Expected result It will sink. Explore 2. Have students put smaller and smaller pieces of clay in water. Materials for each group Clear plastic container of water Clay ball about the size of a marble. Procedure Place your ball of clay in the water to see if it floats of sinks. Does it float or sink? Repeat this process two more times to make smaller and smaller clay balls. The other should be a metallic object with a smaller mass than the wood.

A coin would do. Holding the two objects will give pupils a clear and immediate sense of a difference in mass. Following a prediction about which will float, the two objects can be lowered into a sink or bowl full of water.

For materials, it is some feature of the material, as opposed to the object itself, that determines if it will float or sink. Mass is a characteristic of a particular object. Volume is also a characteristic of a particular object. Density is an intrinsic property of a material. For deciding about objects, again the target concept is the compound property of density, not the contributing concepts of mass or volume alone.

For 6 Resources. Class practical: A group of blocks, all the same size but made from different materials, is used to introduce the concept of Practical Activity