Gifted Issues Discussion homepage Forums General Discussion How to present logarithms to an 8 year old?

My son is doing a project on earthquakes. In order to interpret the Richter scale he is going to need to understand logs.

Obviously, I'll be doing some other research on how to present this, but I saw a recent post about continuous compounding here that got some really great responses.

So I thought I'd throw this out and see if anyone had any advice. If I had to do it right now I'd probably just run through some examples of "taking the log"

Does he know exponents? Logs are when the exponent is the unknown. Does he need to work problems or just understand his data?

He has had some exposure to squares, but he doesn't know exponents.

He only needs to understand the data. That's why I'm currently leaning towards just giving examples. He will be making a seismograph, so he'll have an understanding of the difference between a magnitude 4 quake (which I'm guessing will be bumping the table lightly) and a magnitude 8 quake (really banging the table around?). But I want him to be able to explain how it's expressed with the Richter scale.

Sounds like a really interesting project. Is it for science fair?

{I've been lurking for a long while on this board. Your question made me register.}

I would teach the logarithms as just base ten logs initially, explaining that the number represents how many zeros after a number. log_10(100) = 2, as in 2 zeros after the first digit. Note that earthquake magnitudes scale as log_30, though.

The Richter scale represents the unit measure of the maximum sweep of the s-wave arrival on a certain type of 1930s seismograph placed 100 km from the source.

Now that seismograph:

*Realize that no one uses the Richter scale anymore. The scale is only valid for that type of seismometer and only valid for the Los Angeles basin.

*The Richter scale has been replaced by a variety of measures, all scaled to give approximately the same value for a given event. Each point of magnitude on any scale represents about an additional factor of 30 in total energy release. That's energy release, not displacement or acceleration. I would probably skip that distinction for an 8 year old, though.

*Use the Mercalli scale to give him a decent sense of what the different magnitudes mean.