Earth Tides

In recent weeks my running has had a scientific bent in the spirit of enquiry.

I have got into the habit of running the same route regularly to see how the weather and my state of mind affect my running speed for the same distance.

Only - it is not the same distance.

At first I thought I must be cutting corners - so I carefully stuck to exactly the same route each time I ran. But the distance still varied.

On particularly hot and humid days I have been varying the time of day when I run - sometimes early morning and sometimes evening.

Then I found that the distance varied according to the time of day. Thus:-.

Serial Time of Day Distance Run Time

1. 06-57     10.43 Km     1:01:18
2. 08-12     10.44 Km     1:05:15
3. 12-29     10.46 Km     1:00:42
4. 12-30     10.47 Km     1:03:36
5. 15-44     10.54 Km     0:58:41
6. 16-25     10.46 Km     1:01:11
7. 18-43     10.49 Km     1:03:36

Now my Garmin is pretty accurate on distances. It did match the surveyed distance of the Bath Half Marathon and the 10km distance of the Swindon race.

My conclusion is that I have been measuring the phenomenon known as Earth Tides.

The moon causes tides in the oceans. But the gravitational pull of celestial objects is not just confined to very fluid elements like water but also affects the earth. The largest gravitational pull is from the sun and so this will have the largest effect - much more than other planets or the moon.

So as the sun rises and passes our hemisphere its gravitational pull causes the upper crust of the earth to heave up towards it, slumping down as the sun sets. As with the sea tides and the moon there will be a slight lag - with the highest “tide” occurring after midday. My runs at different times of day record the resulting larger radius curve as a longer distance and the figures reflect this “lag“ with the longest distances - and hence the highest “tides“ after midday.

Except for the run in the evening which shows a bigger figure than the late afternoon run. But this variation could be caused by the gravitational influence of heavenly bodies other than the sun - the figures are not necessarily the same on every day.

For a more scientific explanation, and some mathematics, see CalTech

Or for the rest of us try youtube

There are more things in heaven and earth,Horatio,than are dreamt of in your philosophy - Hamlet.

  

Or - it may just be down to satnav imperfections.