How Are Scales & Balances Constructed?

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Scales and balances are constructed by balancing two objects against one another on something like a spring. Discover how gravity factors into a scale or balance with help from a science teacher in this free video on measurements in physics.

Part of the Video Series: Physics Help
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Video Transcript

Hi, I'm Steve Jones and I'm going to explain how scales and balances are constructed. Scales and balances are essential and we use them an awful lot to measure vital information, particularly mass, obviously, or force. And in fact, there are two basic groups of measuring devices which measure mass or force. That is this, which we call a balance. Strictly it is called a balance for a good reason and I'll explain in a moment. And this, which is also called a balance but we often refer to it as a spring balance. And it is a question of what are we balancing? Here, as you can see, we are balancing one object against another. Here we have a pivot in the center. Here we have two equal length arms and we balance an object of one mass with a set of standard masses. These usually start at a couple of kilograms and go down to a thousandth of a gram, depending on how accurate this device is. Some of these devices will measure to a thousandth of a gram easily and even less. But, generally, this is the kind of thing you might find in the old fashioned kitchen also. So this is a balance which depends on standard masses. We have standard masses. This is not. This is a spring balance. What we know is that if we put an object on the end of a spring, the spring gets longer. If we can put a scale down by the side, if we can add a scale to it, then depending on the length, obviously it goes down here, depending on the length, depends how much weight you put on it. And it is, in fact, gravity that is operating this object. Gravity. Well, gravity also operates this, but not just earth's gravity. We can use this in any situation where we have gravity. This works on the moon as well. This doesn't because the actual gravity stretching the spring is less on the moon. So things weigh less. So, this measures force or weight, and we know that you can be weightless. This measures mass. You cannot be massless. So we have these kind of different objects. This scale is simply something getting longer, shows you that there is more weight. This is a balancing situation where we balance an object against some standard object which we know the weight of. So, that is basically and simply how scales and balances are constructed.


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