Triple Beam Balance: Definition & Use

Triple Beam Balance: Definition & Use
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  • 0:00 What is a Triple Beam Balance?
  • 1:00 How to Read a Triple…
  • 2:22 Practice Problems
  • 3:40 Lesson Summary
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Lesson Transcript
Instructor: Betsy Chesnutt

Betsy teaches college physics, biology, and engineering and has a Ph.D. in Biomedical Engineering

A triple beam balance is a really useful piece of laboratory equipment that you can use to find the mass of an object. In this lesson, learn what a triple beam balance looks like and how to use it.

What Is a Triple Beam Balance?

One day in his science class, Jamie is getting ready to start an experiment. He gathers all his materials and realizes that the first step in his experiment is to find the mass of a wooden block. He wonders how he can find this mass. Is there anything in the lab that he can use? Looking around, he sees a triple beam balance at the end of his lab table. Perfect! A triple beam balance is a device used to measure the mass of an object, so he can use it to measure the mass of his block.

Before using a triple beam balance, you need to know what it looks like and the parts that make it up. Although they may not all look exactly the same, all triple beam balances will have many of the same critical parts.

First, the pan is where you place the sample whose mass you want to find. Attached to the pan are three beams with measuring scales and counterweights on each beam. At the end of the three beams is a pointer that lines up with a scale on the base of the balance.

All triple beam balances will have a pan, three beams, three counterweights, a pointer, and a scale
parts of a triple beam balance

How to Read a Triple Beam Balance

When Jamie places his wooden block on the balance, he notices that the pointer suddenly moves upward, so it's not lined up with the scale anymore. In order to find the mass of his block, Jamie needs to carefully move the counterweights on the beams until the pointer is exactly lined up with the zero line on the scale once again.

First, he should move the largest counterweight one notch at a time until the pointer drops below zero. Then, move the counterweight back one notch. Repeat this process with the next largest counterweight, and finally the smallest counterweight. After adjusting all three counterweights, the pointer should be resting at zero on the scale.

When it is balanced, the pointer should line up with the zero line and rest there without moving
pointer on a triple beam balance

Now, it's time to read the balance to find the mass of the block. The largest counterweight tells you the mass to the nearest one hundred grams. Looking at his balance, Jamie can see that the largest counterweight is still on 0 g, so his block must have a mass that is less than 100 g. The next largest counterweight measures the mass to the nearest ten grams. On Jamie's scale, this counterweight is located at 40 g. Finally, the smallest counterweight measures the mass to the nearest 0.1 g. Jamie sees that the smallest counterweight is located at exactly 1.0 g.

To find the total mass, Jamie needs to add the measurements from each scale:

40 g + 1.0 g = 41.0 g

The mass of this objects is 40 g + 1.0 g = 41.0 g
reading the mass from the beams

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