# Lesson: Measuring Mass with a Triple Beam Balance

David Kujawski Bird Middle East Walpole, MA
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### Lesson Objective

YWBAT: 1) Accurately define matter and mass 2) Accurately read the mass of an object to the nearest hundredth place.

### Lesson Plan

Do Now: What do you know about mass and matter?

Rationale: My incoming 6th graders have varying degrees of science knowledge.  This type of do now gives me a sense of how much they already know.  I don't go into to much detail with mass and matter; it is covered more in the next unit (physical science).

After seeing what they know I define matter and mass on the board.  Matter: anything that takes up space and has mass.  Mass: the amount of matter that something has.

State: "Just like measuring the length of something to see how long or short it is, scientists can also measure that amount of matter that something has."

If you'd like to discuss the difference between weight and mass here, you can.  Weight is the amount of mass something has multiplied by the gravitational pull at a particular place in the solar system.  I go to this website http://www.onlineconversion.com/weight_on_other_planets.htm and show them how much they would weigh on different planets.  They find this to be very interesting, however, my main goal is to teach them the skill of measuring mass...

State: "Scientists use balances to measure the mass of most objects.  Today we will learn how to read a triple beam balance, and tomorrow we will actually use a triple beam balance to measure mass."

Next: Open this site and project it with an LCD projector.

http://www.ohaus.com/input/tutorials/tbb/tbbentry.swf

I like to begin by clicking on the 'balance theory' link at the bottom of the screen.  This gives students a sense of how a balance works.  (5 minutes)

Next: Get back to the original site by hitting the back button and click 'practice weighing'.  I get right into how to use a triple beam balance.  I first emphasize the importance of 'zeroing in' the balance and then model how to read the mass of each beam and add them together to get the mass of the object.

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.

Next: Model using MTB to derive the mass of unknown object.  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'.

Model several examples to the class and then call of students to give you answers to other examples.

TIP!  The tenths place value can be difficult to see.  If you place the cursor over the bottom beam and right click the mouse, you will have the option to zoom in.  If you zoom in once or twice, students in the back will be able to see the numbers!

Classwork Option 1:  You can continue to have students practice by repeating the method above

or

Classwork Option 2: Reserve the computer lab and have student practice on their own.

Checking for understanding:  Circulate around the computer lab and have students show you that they know what they're doing.

Homework: (Homework 1)

### Lesson Resources

 Homework 1   Homework 6,744 Weight on different planets 15896 Triple beam balance tutorial link 15896