Triple Beam Balance

Triple Beam Balance

Middle School

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Learning Objectives

• Identify the main parts of a triple beam balance.

• Describe the process of correctly zeroing a triple beam balance.

• Accurately measure the mass of an object by following the proper procedure.

• Read the total mass by summing the values from all three beams.

Key Vocabulary

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Triple Beam Balance

A precise tool that finds the mass of an object by using sliding weights on three beams.

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Poise

These are the sliding weights on the balance's beams that you move to measure an object's mass.

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Zero Adjust Knob

This knob calibrates the balance, ensuring the pointer is at the zero mark before you start measuring.

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Notched Beams

These are the three beams on the balance with notches to hold the sliding poises securely.

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Parts of a Triple Beam Balance

• The weighing pan is the plate where you place an object to measure.

• ​Notched beams are the three bars that the sliding poises move along.

• Poises are sliding masses you move on the beams to find the mass.

• The zero adjust knob sets the balance to zero when the pan is empty.

• The vane and magnetic dampener help the beam stop moving more quickly.

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Multiple Choice

Which part of the balance is used to calibrate it to show zero when the pan is empty?

• Zero Adjust Knob

• Weighing Pan

• Notched Beams

• Poise

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Step 1: Zeroing the Balance

• Before measuring, you must zero the balance on a completely level surface.

• Slide all three poises to the zero position on the beams.

• If the pointer’s white lines do not line up, it isn't zeroed.

• Rotate the Zero Adjust Knob under the pan until the lines align.

• Always zero the balance after placing any container or paper used for holding the sample so only the sample’s mass is measured.

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Multiple Choice

What should you do if the white lines of the pointer do not line up after you have moved all the poises to zero?

• Wipe the weighing pan clean

• Rotate the Zero Adjust Knob until the lines match

• Place the object on the pan anyway

• Move the largest poise forward one notch

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Step 2: Measuring the Mass

• After zeroing, gently place the object on the weighing pan.

• ​Move the largest poise one notch at a time. Go back one notch if the beam drops.

• Repeat with the medium poise. Then, slide the smallest poise until the beam balances at zero.

• The object’s final mass is the sum of the values from all three beams.

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Multiple Choice

When measuring an object, what is the correct sequence for moving the poises?

• Medium, smallest, then largest

• Smallest to largest

• Largest to smallest

• Any order is fine

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Common Misconceptions: Triple Beam Balance

Misconception	Correction
You only need to zero the balance once a day.	The balance must be zeroed before every measurement.
You can move the poises in any order.	Always move poises from the largest mass to the smallest.
The measurement is final once the beam points down.	If the beam points down, move the last poise back one notch.
The mass is the reading from only one beam.	The total mass is the sum of the readings from all three beams.

Multiple Choice

How does failing to zero a triple beam balance affect the final measurement?

• The final mass will be incorrect by the amount the balance was off from zero.

• It has no effect on the final measurement.

• It only affects the measurement of very small objects.

• The measurement will be consistently accurate.

Multiple Choice

When using a triple beam balance, you place an object on the pan, and the pointer goes up. This means the pan is lighter than the weights. What is the correct next step?

• Move the largest poise forward one notch at a time until the pointer drops.

• Add a larger weight to the pan.

• Remove the object and start over.

• Recalibrate the balance using the zero adjust knob with the object on the pan.

Multiple Choice

A student moves the 100g poise to the 200g notch, and the pointer drops. They move it back to 100g. They then move the 10g poise to the 40g notch, and the pointer again drops. They move it back to 30g. Finally, they slide the front poise to 7.2g to make the pointer balance perfectly. What is the mass of the object?

• 147.2g

• 137.2g

• 247.2g

• 100.4g

Multiple Choice

If you are asked to measure the mass of a powdered substance, you first place weighing paper on the pan. If you zero the balance before placing the weighing paper on it, what will your final measurement represent?

• The mass of the weighing paper only.

• An inaccurate mass that is lower than the actual mass of the powder.

• The mass of the powder plus the mass of the weighing paper.

• The mass of the powder only.

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Summary

• Place the balance on a level surface and zero it before use.

• Move the poises from the largest beam to the smallest beam.

• If a beam makes the pointer drop, move its poise back one notch.

• The object's total mass is the sum of the values on all beams.

Poll

On a scale of 1-4, how confident are you about using a triple beam balance now?

• 1

• 2

• 3

• 4