Question Video: Comparing Tools for Measuring Related Quantities Physics

A beam balance, a spring balance, and a digital scale are types of measurement tools. Which of the following physical quantities is typically measured by a beam balance and by a digital scale? [A] Length [B] Time [C] Mass [D] Weight. Which of the following physical quantities is typically measured by a spring balance? [A] Mass [B] Weight [C] Time [D] Length

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Video Transcript

A beam balance, a spring balance, and a digital scale are all types of measurement tools. Which of the following physical quantities is typically measured by a beam balance and by a digital scale? Is it (A) length, (B) time, (C) mass, or (D) weight? And which of the following physical quantities is typically measured by a spring balance? (A) Mass, (B) weight, (C) time, or (D) length.

Let’s make some room for the first part of our question here, looking at the beam balance and digital scale. Like all balances and scales, beam balances and digital scales measure in units of mass, which are typically grams and kilograms. But digital scales often have a button that when pressed switches the units and can include switching the units to weight, such as newtons or pounds. So, we already know that the physical quantity being measured here is not length and not time. The digital scale can measure mass and weight depending on the setting it is on.

So, in order to figure out which of these physical quantities is typically measured, we have to look at the beam balance. The way that a beam balance measures is by comparing the weight of an object that you place on one end of the scale to a permanently attached weight or weights on the beam. By moving the weights closer or further away, a balance can be found between the object and the beam weight, producing a measurement of mass. This is because by balancing the object and the beam weight against each other, it accounts for gravity, meaning that we’re only measuring mass, not weight, which is dependent on gravity. This means that, unlike a digital scale, a beam balance works just as well on Earth as it does on the Moon.

The physical quantity typically measured by a beam balance and by a digital scale is (C) mass.

Now, let’s clear some space to look at the other part of our question.

Which of the following physical quantities is typically measured by a spring balance? (A) Mass, (B) weight, (C) time, or (D) length.

To use a spring balance, we place an object on the hook at the bottom and then we look at how far the spring extends, measuring from the nearest line at the bottom of the spring. So, at first, it may seem like we’re measuring length since we’re looking at how far the spring extends when we place the weight on it. But this is not actually the case. The spring is just an intermediary. Remember that we’re actually measuring the object attached to the hook, so it’s not length. And since this is a balance, it’s not time. So, we have to determine whether it’s mass or weight that is being measured. The units that are typically written on the side of spring scales are newtons.

Newtons are a unit of weight. And the reason the units are weight is because the spring requires a certain amount of force to compress or extend a certain length. This means that it’s dependent on gravity. So, if we were to go somewhere with different gravity than Earth, like the Moon, then the reading of weight on the scale will be different. So, due to the spring, the following physical quantity that is typically measured by a spring balance is (B) weight.

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