Init << 1/12/2012 by Daniel R. Barnes How to use the Triple Beam Balance Init << 1/12/2012 by Daniel R. Barnes WARNING: This presentation may contain graphical items and other intellectual content that was lifted from the world wide web without the permission of the owners. Do not copy or distribute this presentation. Its very existence may be illegal.

Intro stuff: * Mathematical teeter totter toy thingie * Mass vs. Weight: tbb vs. spring scale

SWBAT . . . . . . zero, adjust, and read the triple beam balance.

The triple beam balance measures mass.

Put the balance on a level surface. Slide all the masses to zero. If the two white lines don’t touch, Rotate the screw under the pan until the white lines do line up.

BELCH Once the scale is properly “zeroed”, put the object to be massed on the pan. (in this case, a delightful little hamster.) BELCH Okay. We’re ready to start moving the sliders, so let’s zoom in on them

Move the masses one at a time, starting with the biggest one. If the pan goes up, you need to move the slider backward one notch and leave it there. Once the big mass is on the correct notch, don’t ever move it again.

If putting the medium mass on 70 makes the pan go up . . . . . . slide it back to 60 and leave it there. Repeat the procedure with the medium mass.

Notice that the large and medium masses have notches on their rails.

Notice that the large and medium masses have notches on their rails. This reminds us that we should never leave the large mass or the medium mass between numbers. We must “click” the large and medium masses right onto the numbers.

Finally, slide the little mass on the front rail until the two white lines match up. Because there are no notches on the front rail, you can slide it to the exact position you want.

Usually, the little pointer on the small slider won’t point exactly to a line. For instance, the slider here is about halfway between 1.5 and 1.6. In such a case, you are allowed to estimate a hundredths digit. Since it’s exactly half-way this time, you could call this one . . . 1.54

This time, the little slider reads . . . 4.71 or so. Can you see how the pointer is just a little bit past the 4.7? Maybe you think it’s closer to 4.72 than it is to 4.71. This is where the measuring process loses some of its precision.

This time, the little slider reads about . . . 3.39. Can you see how the pointer is almost to the 3.4 but not quite?

This time, the little slider reads about . . . 8.24. This time, the pointer is about halfway between the 8.2 and the 8.3 marks, but it’s just a bit closer to the 8.2.

And now . . . some scale-reading practice.

Ok. I get it. That’s enough practice reading the numbers. 521.2 grams Triple Beam Balance Demonstrator by Daniel R. Barnes, init 9/18/2006

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TRIPLE BEAM BALANCE TIPS * ZERO THE SCALE before working with it. * BIG mass first, MEDIUM second, then SMALL mass. * Never leave the big or medium masses between numbers. (Notice the NOTCHES!) * NO TURNING BACK: Once you’ve got a mass in the right spot, don’t move it again. * USE PENCIL ON LITTLE MASS: Use the tip of a pencil to move the little mass once you’ve got it close to the right spot. This keeps you from knocking the scale arm and making it rock up and down, wasting your time.

TRIPLE BEAM BALANCE PRACTICE You and the person sitting next to you must decide who is person A and who is person B. Person B, go get a triple beam balance from the cart if you need to. Carry it with two hands. Treat it gently. Person A, zero the scale. Wait for teacher approval. Person A, determine the mass of a phone or wallet. Record its mass AND what each slider reads, in your notes. Describe where the little slider is.

MORE HANDS–ON PRACTICE Partner B should now measure the mass of his/her phone, calculator, or wallet. Record, in your notes, what each slider reads. Describe where the last slider is. Now, partner A should measure the mass of a piece of paper. Partner B should now measure the mass of a paperclip. Partner A should now measure the mass of his/her student ID card. Next, partner B should try to measure the mass of a pencil or a pen.

even more HANDS–ON PRACTICE Measure and record the “tare” mass of an empty 50-mL graduated cylinder. Fill the cylinder up to the 43-mL mark. Measure and record its “gross” mass now. Use math to determine the “net” mass of the 43 mL of water. What do you conclude from the data about the water? Repeat the above procedure with 28 mL of water. This time, let someone else get their hands on the materials. What does all this tell you about the density of water?