Mobile phones and other smart devices are packed full of sensors that students can use to collect data on temperature, pressure, light intensity, relative humidity, sound, acceleration and vibrations and there are a huge number of free utility apps that can be downloaded and used to turn these sensors into seismometers, rangefinders, anemometers, speed guns and heart monitors. What’s more, such apps provide quick and easy ways to engage students in fun problem-based activities with minimal resources. **It really gets them thinking!**

Here’s a **‘Hackshop/Appshop’** that @ka81 and I run as an ice-breaker to get students thinking about (a) how to solve problems and (b) how useful their mobile phones and smart devices can be! We give them about 10 minutes per question and usually run it in groups of 2-3 so that they can all get involved.

**Here’s how it works…**

Each group of students is given a **‘tray of stuff’** containing the following; A 133mm long piece of wire (we usually use a male-male jumper wire), a cardboard right-angled triangle, two coins (we give them a 2p and a 1p), a piece of *blutak* that has exactly the same mass as one of your coins – we use 3.56g, the mass of a 1p), a piece of thick card (it has to be stiff), 2 rubber bands, 3 pencils, scissors and sticky tape. These are the KEY ITEMS you need. We also throw into the tray a random assortment of odds and ends; paper, batteries, paperclips, anything you like. These are really red-herrings, because all the problems can be solved using the key items, but it makes for a more interesting lesson! Students are told that they will be given a number of problems to solve and that they can use their mobile phones / tablets and anything in their ‘trays of stuff’ to solve them, but nothing else. We then set them the first question.

**QUESTION ONE – How long is the piece of wire?**

It doesn’t students long to figure out that without a ruler they need some frame of reference. They need to know the measurement of ‘something’ in order to use it to create some kind of scale. Our experience is that their first choice of solution is not usually the obvious one, which is to **download a ruler app** on their phones and actually MEASURE the wire 🙂 No, what most do is to Google the diameter of the 2p coin (25.9mm) and the 1p coin (20.3mm) and use multiples of these to work out the length of the wire. At this point many get stuck because they quickly find that 133mm is neither an exact multiple of 25.9 nor 20.3 and so decide their approach has been wrong. You see, this where we were a little trixky, it’s actually the length of (2 x 2p coins ) + (4 x 1p coins)… some figure this out… whereas other abandon using the coins and finally cotton on to the fact that they can download a phone app to do the job. The most ironic solution to the problem we had was one group of students who Googled the DIMENSIONS of their mobile phone and then used their actual phone as a (very) crude ruler. Others made the mistake of getting an image of a ruler on their phones and tried to use this…until we pointed out that the scale wasn’t going to work unless the ruler was ‘life-size’ 🙂 Whatever their initial approach, it’s a simple way to give them a wake up all regards simple ways to solve problems using apps. We then discuss with the students the various uses to which such an app might be put. One point to note… you have to use wire… string stretches!

**QUESTION TWO – what are the three angles on the cardboard triangle?**

Students again typically head in totally different directions with this question. The simple solution is to **download a protractor app** and simply measure the angles directly…but again, students rarely do this straight off the bat. Instead many get stuck with the ruler app idea and resort to using the ruler to measure the sides of the triangle and then try to Google Pythagoras’s Theorem and use their phone’s calculator to do trigonometry. Some use a low-tech phone based solution approach… they simply go to Google images and find **an image of a protractor** and use this to measure the angles by placing the triangle on it. Again, we round off the question by discussing the various solutions and the ways in which such apps can be used.

**QUESTION THREE – what is the mass of the blutak?**

Of course if you want to make this a little more silly and fun you can shape the *Blutak* into something… we have used rabbits in the past 🙂 What’s the mass of the rabbit? SO, by question three students have got the idea that their first port of call for solving our little problems is to **download a phone app for it**, so when faced with THIS question they naturally look for an app to weigh the *Blutak*. This is rather sneaky of us to be honest, because most of the apps don’t work and those that do, require something that we have deliberately left out of their trays – a small polythene bag. Most students quickly find and manage to download a scales app **BUT be careful here** and consider the age of your students because the top hit for a search of ‘scales’ on Android’s playstore gives you the **‘ Weed Scale‘ app**… and yes, it does what it says on the app! Either way, when they put the

*Blutak*on the phone scales of their choice, nothing happens. Here’s why. Weighing apps use the phones accelerometers to measure movement of the phone when a mass is applied BUT it relies on the tiny displacement of the phone due to its slightly increased mass and when you put your phone on a hard surface it has nowhere to go. This is why you need the small polythene bag we’d deliberately left out. If you partially inflate it and sit your phone on top THEN add additional mass to the the phone (e.g. your

*Blutak*) the phone ‘sinks’ a bit into the soft bag and this movement is detected by the phone’s accelerometers and converted to mass by the app’s algorithm. Cool huh? Well it is, but in the absence of a poly bag, not an option our students could use…but it generates a lot of intersting discussion about the use of apps, phone sensors and their limitations!

So, how can you solve this particular problem without an app using just the items in the tray? Answer, build yourself a small balance from the bits in your tray (see image below). Here’s how: cut a strip of stiff card about 12cm x 1cm. Tie the three pencils together with the rubber band so that they stack lengthways into a triangular cross section (stops the fulcrum of your balance wobbling). Place the card over the fulcrum like a see-saw. Place your *Blutak* on one end and your 1p coin on the other and the two perfectly balance… your *Blutak* therefore has the same mass as the 1p. Google the mass of a 1p and you have your answer = 3.56g. The most ingenious solution we came across was a group of students who solved the problem (albeit not quite as accurately) by forming the *Blutak* into a cuboid, measuring it’s dimensions using a ruler app, calculating its volume and the Googling the density of *Blutak* to calculate the mass – very nice, and not one we’d thought of! You never can tell how students are going to solve problems… so never underestimate what YOU can learn during such activities 🙂

There are literally dozen of other ideas you could come up with along similar lines, so if you do, we’d love to hear from you!!!