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# How to Test your GPS (and fill up classes with interesting but manageable practicals)

Many us on here are indebted to the (UK) National Physics Laboratory for their Virtual Physics Laboratory, put together by John Nunn and made available for free to teachers in Ireland who attend one of the frequent training sessions run by the IoP.

But I hadn't until recently explored their website and so was unaware of the great 'measurement-at-home' page which is full of interesting-but-practical activities and which could be a real goldmine of ideas over the next few weeks - particularly with junior years. Particularly coming into the summer. And particularly coming into the summer with junior years and without the threat of exams to keep some sort of order and focus.

Some ideas will be familiar: checking reaction times with a dropping ruler, or measuring how the height of a bounce is affected by the temperature of the ball, for example, But others were new to me, such as calculating the energy-efficiency of a candle.

But the one I've got most out of so far, is the one labelled 'where on earth am I?' This simple activity allows us to check the reliability of the GPS function in most of our phones, while also teaching students how the GPS system works, and investigating to what extent it's affected by being inside a building.

As with all of the suggested activities, it's really well explained and has an introductory video, but the essence of it is this:

• choose an exact location for your phone (maybe the corner of a desk)

• note the latitude reading to 6 decimal places

• walk around a bit to force it to reset

• repeat a few times

• subtract the smallest measurement from the largest, and multiply by 110,000

This will yield any variation between the readings in metres. Obviously all the readings are in the same location so any variation is a good measure of precision, or the lack thereof. The NPL suggests doing it indoors and then outdoors and comparing the results, but I didn't have time to go that deeply into it.

For the record, We checked six phones: one was out by 13 m, four were out by around 30 m, and one was out by.....970 m!

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