This page has been translated from Italian

My son is in second grade, but, like his sister , is a very curious child so today, while I was watching an electrocardiogram, comes up and asks me what I'm doing.

See, I make on this strip of paper is designed our beating heart. In the background are designed for large large checks. Five big squared is equivalent to a second. This, for example is a heart that beats once every second. See? Every five large checks, ie every second, there is a heartbeat.

As her heart beats once every five big squared, ie once per second, how does this heart beats per minute? Philip is an intelligent child is immediately to respond. A beat per second, sixty seconds in a minute, then the heart represented above beats 60 times per minute.

Philip Fine, but what if now the machine that makes the ECG will print a sheet in which the heart beats each square box that is five times faster?

How many beats per minute will now this heart? Philip's answer is almost immediate, if beats 5 times faster than before then beat that three hundred sixty five times a minute.

Okay Philip, so far is easy. But now comes the hard part. And if, instead of a beat every five large checks, large checks every two beats?

Philip was not discouraged and, after thinking a little, 'I says, means that is two times slower than when he went five times faster. Bravo Philip, and then? So, if when he went five times faster than it was 300 beats per minute, now that is twice slower, will 150 beats per minute.

Ok, and now makes a beat every three large checks.

This time Philip understood the trick and immediately tells me that my heart will go three times slower than when it was 300 beats per minute ie moment's pause, 100 beats per minute.

Bravo Philip latter case, what happens to the beats per minute when it is instead a beat every four large checks?

I immediately replied that the heart will be four times slower than when it was 300 beats per minute. This time, however, needs paper and pencil to divide 300 four times but the result gets to wait and soon we hear his voice ringing answer 75.

Now I wonder if my son in second grade he realized this, because a university student of medicine they say, a square box 300, two large checks 150, 100 three large checks, four large checks 75, 60 and five large checks when someone asks why instead of using the trivial explanation above, it is from the fantastic first response: "because it is signposted, so you can find it signposted" and then, because, from our faces, the explanation does not seem to be satisfactory, you begin to pull out the uniform rectilinear motion of the paper and, to my attempt at an explanation, she gets out the fact that "oh well, but a doctor mica can get to come to terms."

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