Isn’t the answer to the question, “What does a scale measure?” quite obvious? For many, the answer is it measures our weight in kilograms, grams, or pounds (lbs), but is it the correct answer? Well, technically, it isn’t because kilograms or pounds are measuring units of mass. However, the scale measures something different, which is actually force.
In fact, if you get into more technicality, you may also have to ask if it measures our mass or our weight, because, by the definition, mass and weight are different.
What Does a Scale Measure?
The answer is not as obvious as you initially thought, right? The scales actually measure the force, which, if you remember your science class in high school, is measured in Newtons. The scale first measures the downward force and then convert it into kilograms or pounds.
So, how does it do it? How does it measure force? And how does it convert Newtons into kilograms?
The answer lies in the design of the scales we use. Almost all scales use springs that are concealed inside the mechanical structure of the scale. These springs actually measure the force that you exert on them when you stand on the scale.
How Does a Scale Measure Force?
When you stand on the scale or place something on it, the force you exert on the scale reduces the size of the springs. The scale actually measures the size of the spring to calculate the force. The shorter the size of the spring, the more force you are exerting, and thus the more weight you have.
The spring used by the scale is connected to the dial that is visible to you on each scale. When the size changes, the dial moves as well and tells you about the actual weight you have. In digital scales, modern technology is used to convert the difference in the size of the springs into the weight displayed on the screen.
What Do We Need to Measure: Weight or Mass?
However, here is the problem. Weight is actually the pull of the gravity on our body or any other object. The issue here is gravity changes for different planets, doesn’t it? For example, if you use the same scale on the moon, it will show you a different weight, as the force of gravity is much less than that of the Earth.
For example, if you weigh 70 kg on Earth, you will weigh only 11.6 kg on the moon. However, if you use the same scale on Jupiter, your weight will increase to 165 kg due to higher gravity on Jupiter. On the sun, you will weigh more than two tonnes!
To help you differentiate the two, here are the scientific definitions for both weight and mass.
- Mass: It is the amount of matter contained within our body or any object.
- Weight: It is the measurement of the force of gravity when applied on an object or given an amount of mass.
Even when you have different weights on Earth and moon, or on any other planet, the mass of your body remains the same. This means your weight may vary depending on the place you are using the scale, but your mass doesn’t.
Here is another difference. Kilogram or pounds are the measuring units of mass, not weight. As weight is also a kind of force, the pull of gravity on us, the measuring unit for weight is Newton as well.
Even though mass and weight are different, they are also linked with each other. If you go back to your high school science class, you will remember that objects with mass attract each other, right? The larger the mass an object has, the larger the force of attraction.
This is why, the larger the mass you have, the more weight you have. As the force is directly related to the mass, you will exert more force on the scale if you have more mass, and less force when you have less mass.
So, What Does Our Scale Tell Us?
As mentioned above, the measuring unit for weight or force is Newton. Does our scale show us Newtons? No, it doesn’t. So, it certainly does not tell us about weight.
On the other hand, the measuring unit of mass is kilograms or pounds (lbs), which is the unit our scale shows us. This means that our scale measures mass even when it uses the mechanism that calculates the force you exert, but later convert it into kilograms.
You can also see it as our scale reflects the measurement of our mass, but in reality, it is actually measuring force or in simple words, weight. This is obvious, as the same machine will show you a different measurement on the moon.
Does your mass change when you travel to the moon? No, it doesn’t. This means that the scale is showing you a wrong measurement of your mass, as it fails to convert the weight into mass due to change in gravity.
You can also do another experiment when standing on the scale. If you put your hands on a wall or something fixed and exert a downward force, the reading on the scale will increase. Again, your mass doesn’t change, but the reading increases on the scale due to more force.
Here is a simple fact. More people when using scale confuse that mass and weight are the same things. However, they are not. When we are using a scale, we actually want to learn about the mass we have, and this is what the scale shows us when it reflects the result in kilograms or pounds.
However, the scale is not measuring our mass. It just measures the force, which is our weight. It simply converts the readings from the force we exert into the measuring units of mass for our understanding.
So, what does a scale measure, really? The answer is, force or weight, but what we read on the scale is the measurement of our mass. However, you cannot use the same scale on any other planet to measure your mass, as you have to adjust the conversion of Newtons into kilograms according to the gravity of each planet.