Question Video: Understanding Fundamental Quantities Physics

Can the quantity “speed” be defined by multiplying or dividing fundamental quantities?

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Video Transcript

Can the quantity speed be defined by multiplying or dividing fundamental quantities?

To answer this question, we should begin by recalling what is meant by the quantity speed. The speed of an object is defined as the distance moved by that object per unit of time. So, for example, if an object moving with a constant speed traveled a distance of one meter and it took a time of one second in order to do this, then we could say that the speed of that object was equal to one meter per second. Taking a look at the units of this value of speed, we can see that we’ve got meters, which is a unit of length or distance, divided by seconds, which is a unit of time.

Now we can see that these units make sense in the context of this definition of speed. The quantity speed is equal to the distance moved, which is a measure of length, per unit of time. This means then that the quantity speed is equivalent to the quantity length divided by the quantity time. Now on the right-hand side of this expression, neither of the two quantities length or time can be separated into more fundamental parts. Quantities such as these that consist only of themselves and can’t be separated into more basic or fundamental parts are known as base quantities or fundamental quantities.

We know then that the quantity speed can be written as length divided by time, where both length and time are fundamental quantities. This equation defines the physical quantity speed in terms of two fundamental quantities, length and time. And so our answer to this question is that, yes, the quantity speed can be defined by multiplying or dividing fundamental quantities.