Measuring Volume of Irregular Objects Using Water Displacement

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Objective

SWBAT: Measure the volume of various irregularly shaped objects using water displacement.

Big Idea

Students need to be exposed to various ways of measuring volume and building science skills. This lesson show students how they can measure the volume of an irregular object.

Lesson Overview

This lesson has students watch a TEDEd video that tells the story about Archimedes' discovery of volume and then has them develop a way to measure the volume of irregular objects.  Emphasis is placed on getting students thinking about the idea that objects take up space and therefore displace water, based on the amount of space occupied by the object.  

Students come up with several methods to measure the volume which is then used to introduce the importance of using a standardized instrument known as a graduated cylinder.

Although this lesson doesn't necessarily address a specific content standard, it helps students establish a deeper conceptual understanding of what volume means and how it can be measured.  In the process students develop their ability to Plan and Carry Out Investigations (SP3).

Using a Story to Hook Students

10 minutes

I want to get my students thinking about the concept of volume and water displacement prior to actually calculating volume of irregular objects.  I ask them how they would calculate the volume of a crown with irregular shape.

Field student responses and then show them this video:

Ask students why they can't calculate the crown's volume by using length x width x height.  Have a discussion and then get into how scientists measure volume of irregular objects using Archimedes' Principle.  

Ask students to come up with a way to measure the volume of irregular objects and circulate around the room listening to their discussions.  Then have students share their ideas.

Building off of Archimedes Bath Tub Discovery

20 minutes

I want to add a student-centered element to this lesson, as opposed to just showing them how to use water displacement to find the volume of irregular objects.  I start by asking students how they could take Archimedes discovery of water spilling over the side of the tub when he got in to explain how they could find the volume of an object.

Planning and carrying out investigations in 6-8 builds on K-5 experiences and progresses to include investigations that use multiple variables and provide evidence to support explanations or solutions.

  • Plan an investigation individually and collaboratively, and in the design: identify independent and dependent variables and controls, what tools are needed to do the gathering, how measurements will be recorded, and how many data are needed to support a claim.

  • Conduct an investigation and/or evaluate and/or revise the experimental design to produce data to serve as the basis for evidence that meet the goals of the investigation.

  • Evaluate the accuracy of various methods for collecting data.

  • Collect data to produce data to serve as the basis for evidence to answer scientific questions or test design solutions under a range of conditions.

  • Collect data about the performance of a proposed object, tool, process or system under a range of conditions.

 

I ask students: How can we find the volume of the crown?

I give each group about 10 minutes to discuss what they would do. I structure the discussion so that it builds student thinking, starting with a dig into their own thinking, and then growing ideas through sharing.

Structure of group work:

1) Everyone silently sketches a picture and describe (with words) what they would do. (3 minutes)

2) One student at a time, per group, has 1 minute to share what they would do. (4-5 minutes)

3) Groups decide what they would do, based on everyone's input, (5-8 minutes)

4) Each group then shares with the class what they would do.

I ask what they would use to measure the volume and take responses.  I then transition into introducing a graduated cylinder and how it works.  

Using Graduated Cylinders to Measure Volume of Irregular Solids

25 minutes

I first show students how to calculate the volume of irregular objects on a worksheet.  This builds their confidence before they are asked to calculate the volume of actual irregular objects using water displacement.  

I model one or two examples and then allow students to complete Practice Worksheet with a peer.

We review their responses to the worksheet and then transition to practicing measuring volume with water displacement.

 Since students already know how to read a graduated cylinder at the meniscus I only give them a reminder. If you haven't covered this, be sure to do it now.  I carefully note the water level, exaggerating this action to draw attention to this critical first step. Then I demonstrate the proper way of tilting the graduated cylinder and sliding the object in, being careful not to lose any water.  I then say that they should subtract the old volume from the new volume to find the volume of the object.  

I have six stations set up for student groups to circulate through. Each station has several items to measure.  Groups circulate at the designated times and we review the volumes of various objects at the end of class.  

Note:  Make sure that the objects fit in the graduated cylinder.  Another useful activity is to have kids compare the volume of the same object using two different containers, such as a graduated cylinder and a beaker.  You can point out the error that occurs when we don't use the appropriate instruments in labs and discuss how that can affect our results.