I Can Measure Mass, Not Weight, With A Triple Beam Balance!

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SWBAT accurately read the mass of an object to the nearest hundredth using the MTB (Middle, Top, Bottom) Strategy on a Triple Beam Balance.

Big Idea

Now that students have a clear understanding between mass and weight, they can learn how to measure mass using a triple beam balance. By utilizing free online tools students become comfortable reading a balance before using one.

Reviewing the Difference Between Mass and Weight

5 minutes

Students learned an important distinction between mass and weight in the prior lesson, so take some time to review the concept, discuss evidence to support their understanding and address any lingering questions.

I review the homework from the previous night.  Depending on the class they either continued writing their SEA formatted response or answer the writing prompt.

You may even consider having students watch this engaging video (Weight vs. Mass by Remi-Rix the Science Chick) to get their minds thinking about mass vs. weight again.

Modeling Reading Mass On a Triple Beam Balance

5 minutes

I have this website open prior to class beginning.

Notes on board: I write MTB on the board, which stands for Middle, Top and Bottom beams on the balance.  I explain to the students that I start reading the middle beam, because it represents that largest number value (hundreds) and then move on to the top beam which represents the tens number value.  Finally, I add the middle and top measurements to the bottom measurement (ones and tenths).  The logic is that you start by adding the largest numbers first and then the smaller numbers; this makes determining the mass of the object easier.  Students record notes in their science notebooks.

I then model how to use MTB beams to derive the mass of unknown object.  This is an interactive web site and I'll describe here how I use it in this lesson. I hit the next button at the bottom right corner on the OHAUS triple beam balance scale reading website.  Then click new unknown at the top middle of the next screen.  The weights on the beams will move and you will have to use MTB to get the correct mass.  Once you know the mass, type your answer into the 'Enter your weight here:' space and then hit 'check weight'. 

I repeat this a few times until I feel that the students are ready to try it on their own.

Students Discovery and Practice

30 minutes

The Ohaus website has many great features that students can click on to find out more about the theories behind balances and proper care, especially how to carry a balance in a lab.  I first have students practice measuring using MTB.  Once they can comfortably determine the mass of the objects, I ask them to click on each section on the website and record at least 2 important concepts or tips in their notebooks.

 Here are other pictures of students practicing measuring mass.

We then wrap up class by reviewing some of the tips and concepts learned, especially how to carry a balance, how to zero in a balance and the importance of doing so.  We will get into this more tomorrow when we actually use balances.


To help students remember, through practice, I hand out this worksheet as homework. It is practice in reading the weights shown on a TBB.