Summary:

The purpose of these tutorials is to teach students about the density of objects and water. Through hands-on activities students will hypothesize, test and record their findings as they experiment with the density of different objects.

After this lesson, students will be able to:

• Understand the basic properties of density
• Identify and explain the difference between the density of different objects
• Demonstrate how to test the density of different objects

Recommended Grades 4-8th

Introduction:

Have you ever wondered why two objects that are the same size and shape can have different weights? Or how a larger object can be lighter than a smaller object? This is caused by an object's density which is its mass and volume. Everything is made up of tiny particles that we can’t see, and how dense an object is depends on how much space is between the particles of a particular object. In fact the density of an object can even help determine what it is made of!

Graphic displaying density of particles

Just like solid objects, water also has density which determines if an object will sink or float. Objects that are more dense than water will sink and objects less dense will float.

Materials Needed

• Cup
• Water
• Grape
• Orange
• Sugar

Experiment 1: Sink or Swim with a Grape
Using the video demonstrations provided, test, analyze and document the results of your experiments with your partner.

Questions & Hypothesis/Assessment:

First: Will a grape sink or float when placed in a cup of water? Write down what you think will happen.

Test

Next: In a second cup of water, add a 1 cup of sugar and mix. Now the density of the water has changed do you think the same grape will sink or float? Write down what you think will happen when you place the grape in the water.

Test

Conclusions: Were your predictions right? Did the grape sink and float when you expected it to? Did it float in one liquid and sink in another? Why do you think they acted the way they did?

Experiment 2: Orange Denisty

First: Will an orange sink or float when placed in water? Write down what you think will happen when you place the orange into the water.

Test

Next: Now peel the rind of the orange, will the peeled orange sink or float? Write down what you think will happen when you place the peeled orange into the water.

Test

Conclusions: Were your predictions right? Did the orange sink and float when you expected it to? Why do you think they acted the way they did?

The unpeeled orange floats because the rind is very porous and filled with tiny pockets of air. Even though you're removing mass when you peel the orange, the peeled orange becomes more dense than the water and sinks.

Sink or Float Experiments Continued:

Now that your students are more familiar with the density, have the students test and assess the density of different items like a penny, leaf, marble etc to see if they will sink or float and record their findings and observations.

Vocabulary

• Density – is the amount of mass per unit of volume
• Matter – is everything that exists that can be seen and touched
• Volume – is a measure of the amount of space that a substance or an object takes up
• Mass – is a measure of the amount of matter in a substance or an object

Facts about Density

Density of an object can determine what it is made of.