How long would it take to fall through the Earth?

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This is a classic calculation, and one that’s surprisingly tricky: suppose you could bore a hole all the way through the Earth. If you jumped in, how long would it take you to fall through and come out of the other side?

If you’re taking A-level physics you know pretty much everything you need to do the calculation for yourself, but there are a few fiddly little problems you need to deal with along the way. Most importantly: if you’re falling through the Earth, only some of it is below your feet. The rest of it is above your head, and the force of gravity from that part is pulling you not downwards but upwards. So working out the forces isn’t as simple as you might hope, but you do get something back: when you start picking away at the maths, you’ll find that what happens when you reach the centre of the planet is pretty important.

Have a think about how you’d tackle the problem yourself, then take a look at this video from MinutePhysics.

Tip of the hat to Alom Shaha for pointing us to this.

Engineering principles: keep it simple

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We’re developing a neat little workshop based around catapults, bits of which have sneaked out into the world in test events over the last couple of months. The core of the challenge is the simplest possible catapult we could dream up, which uses a paper cup, elastic band and a plastic spoon to fire a table tennis ball at least five metres. It’s tremendously satisfying, but it’s not quite enough on its own for the workshop.

My Mark II Catapult uses the same basic ingredients, but pivots the spoon on a kebab stick bearing. It’s even more satisfying, but a little more fiddly to make and – annoyingly – slightly less effective in range.

This morning: the Mark III Catapult, which uses the elastic band as a torsion spring. It’s fiddly to make, pushes the limits of cardboard cup rigidity even more than the other designs, and…

…is almost completely ineffective.

Back to the drawing board, with one key engineering principle ringing in our ears: keep it simple.

Turns out motor racing might be useful after all

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The Formula 1 Championship is a strange beast. I’m not alone in having become thoroughly bored with the political wranglings around it, and I’ve drifted far enough away that I no longer even recognise most of the team names. So it’s something of a surprise to learn that the engineering work going on behind the scenes might still be – whisper it – relevant and useful.

Animagraffs car engine

Click for animated diagram of an internal combustion engine, from the excellent Animagraffs.com.

Burning petrol in a car engine is fairly mad in the grand scheme of things, partly because internal combustion engines are horribly inefficient. They typically bumble along around the 20 or 25 per cent thermal efficiency mark: only one fifth or so of the energy input (in the form of petrol) is turned into useful work. That’s not necessarily a great surprise if you look at everything that’s going on inside an engine –  click the picture for a brilliant Animagraffe page illustrating the four-stroke engine cycle. Car engines get hot, and that heat isn’t doing anything to propel you down the road.

Diesel engines can head up towards 40% efficiency, but even as recently as 2014 it was big news when Toyota managed to hit 38% for a petrol engine, which I think is the one currently in their latest Prius hybrid.

So a rumour that the Mercedes and Ferrari F1 teams have petrol engines that achieve somewhere around 47% efficiency is eye-catching. They’re managing this thanks to German engine component supplier Mahle, whose design adds a secondary combustion chamber linked to the main cylinder head. The spark plug ignites a fuel-rich mixture in that secondary chamber, blasting a turbulent jet of burning gases into the leaner mixture in the cylinder. That leads to more complete combustion, and hence a more efficient engine overall.

Now, internal combustion engines are at their most efficient when they’re operating under load (ie. accelerating) and with the throttle full open (ie. accelerating hard). Which is more like the typical situation for Formula 1 engines than a daily commute, bumbling along in nose-to-tail traffic. So gains at the racing circuit don’t necessarily mean as much on the public road. Nevertheless, the thought that there are still major gains to be wrung out of old engine technology is surprising, and encouraging. Maybe we’ll see some of these ideas in road cars in the not-too-distant future?

Read more about the ‘Turbulent Jet Ignition” technology in this excellent Ars Technica article.

In fact, engine technology remains a huge field of research. Here’s engineer Hannah Petto giving a behind-the-scenes peek of the engine test facilities at Caterpillar’s engine research site, here in the UK, outside Peterborough:

The racing teams may have all the showy glamour, but there’s similar sorts of work going on for construction and agricultural machinery.

Not-so-coincidentally, the Think Physics office is currently reverberating to the sound of power tools and hydraulic hammers, as the building here at Northumbria University is being partially rebuilt to accommodate – amongst other things – a new engine test facility similar to the one Hannah shows in the film. It’ll be used to help deliver the new Automotive Engineering degree course we have starting up here from September this year.

The future may rest in electric vehicles, but we’re a long way from done with internal combustion.

A-Level Physics teachers: your thoughts welcome

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A few months ago, we made a film of an A-level core practical: measuring g via the free-fall method. Many teachers responded to our invitation to comment, and to our shameless request for recommendations for funders. Well… that worked. Thanks for your kind words, and thanks to your kind words we’re making more of these films. We’re not yet revealing the funder, but we can reveal the first three (or four) practicals we’re filming. We’d also like your help again.

We’re filming next weekend, 21st/22nd May, and we’d be delighted if these films could reflect your experience with practicals you’ve completed, your thoughts about ones you’ve yet to teach, and so on. We’ve a crack team of advisors and supporters already involved, but nothing beats the broad experience of teachers across the UK (and internationally).

So: here are the outlines of the films we’re planning to make. Please leave a comment below if you’ve any pertinent thoughts. It’s extremely helpful if you sign your comments with your real name, and note your affiliations (ie. school, that you’re a teacher / head of department / examiner etc) if appropriate. As before, the films are intended primarily to support teachers, but may be of use to students for revision purposes.

Laser diffraction

  • Introduction to traditional two-slit diffraction apparatus, with recap of explanation.
  • Plotting slit/screen distance vs. slit spacing.
  • Discussion of laser safety issues and suppliers.
  • Suggestions around practicalities, and the value of the practical for exploring issues of experiment design.
  • Alternative arrangement using a wire rather than traditional double slit.
  • Second alternative using diffraction gratings and vertical arrangement.
  • (possibly – this film’s already getting quite long!) third alternative using diffraction from a CD, as suggested by OCR.
  • Discussion of historical context and significance.

Finding the EMF and internal resistance of a battery

  • Conceptual basis of internal resistance; review of relationship between EMF, terminal potential difference, current and internal resistance.
  • Apparatus, using multimeters, variable resistor, bare wire contacts.
  • Variations, including array of known resistors; switched contact; analogue meters.
  • Comparison of internal resistance of different battery types.
  • Discussion of value of this practical for exploring key lab skills, including careful but quick working.

Discharging a capacitor through a resistor

  • Using a data logger to explore capacitor behaviour.
  • Initial verification of \(V = V_0 e^{-t/RC}\); demonstrating that voltage decay half-life is constant, and the time taken to decay to \(1/e\) of the original value.
  • Manipulation of \(V = V_0 e^{-t/RC}\) to a form comparable with \(y = mx + c\); processing and plotting data accordingly.
  • Low-budget version of practical using voltmeter and stopclock, and with hand-processing of data.
  • Extend the practical to finding the value of an unknown capacitor.
  • Discussion of error.

Force on a current-carrying conductor in a magnetic field

  • The standard ammeter and balance arrangement.
  • Sequence of
  • Determining magnetic field strength.
  • Alternative arrangement with U-shaped wire segment.

Thanks in advance for all your comments and suggestions. Inevitably, we won’t be able to incorporate everything everybody suggests, but if you’ve come across a brilliant way of covering one of these practicals which we’ve not mentioned above, or have thoughts on aspects your students find particularly challenging – we’ll do our best to incorporate your ideas.

Final note: this post was written by Jonathan. Hello. I’m the film-maker behind all these videos, and while I am technically a physicist, I last saw most of these practicals in my own A-level studies more than 25 years ago. Any glaring howlers in the above are due to my misunderstanding of the scripts, and you can be reasonably confident that the many teachers involved in the filming will politely roll their eyes before we commit film-based crimes against physics.

Watch this marble run with magnets

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Brilliantly inventive. See if you can work out how all the different mechanisms work – there are some amazing and subtle ideas in here. Great stuff.

Tip of the hat to Joe for spotting this as it hit Digg this afternoon.

View the transit of Mercury on 9th May

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This May will provide us with a fantastic opportunity to observe a transit of Mercury. It should be possible to view the eclipse from your school or home, but we will need to keep our fingers crossed for good weather.

What’s a transit of Mercury?

Like a solar eclipse, when the Moon obscures the Sun, a transit occurs when Mercury or Mars (the only planets between us and the Sun) partially block the view of the Sun from the Earth. A transit is much rarer than a solar eclipse. A solar eclipse may occur a few times a year, while transits of Mercury occur between 3.5 and 13 years apart, and transits of Venus come along only every century or so.

The next transit of Mercury will start just after midday on 9th May and will finish at around 7:40pm

How to observe the transit safely

The best way to observe in a group is to project an image of the Sun onto a shaded white surface using a telescope. CLEAPPS Guidance leaflet provides excellent information about how you can set this up: www.cleapss.org.uk.

However if you do not have a telescope, or the weather is poor on the day, live streams of the transit will be available on the internet.  ESA will be providing one and the link will be provided on their website closer to the event.

 

Never look directly at the sun!

You could permanently damage your eyesight

 

Activities

The Royal Astronomical Society have produced a teachers activity pack (PDF link) which contains a range of different worksheets and activity suggestions for use with primary and secondary students. The pack also supports literacy and numeracy, and features Mercury-themed cupcake investigations.

You could ask pupils to compare the size of Mercury and the Sun. They could do this by looking at the diameter of the two objects, the area of the disc, or their volume. Which approach gives the best idea of the relative scale of the two? NASA has created a solar system explorer website that will help students investigate further.

 

 

British Science Week. That’s all for now, folks!

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Each March, British Science Week celebrates the awesomeness of science, technology, engineering and maths. Over this year’s week, from 11th – 18th March, Think Physics joined in the fun by opening up specially-designed workshops and lectures to schools from across the North East. The result was a fantastically action-packed and rewarding week of workshops. We had Key Stage 2 students making Incredible Machines and Key Stages 3 and 4 investigating Rollercoaster Physics.

In Incredible Machines, pupils explored the simple mechanisms of gears and linkages and made their own machines from cardboard and paper fastners. The workshop invited children to look at the role of engineers in designing and creating machines which help shape the world around us.

In Rollercoaster Physics, pupils got hands-on with rollercoasters, building their own K’nex test track and using data loggers to measure the speed of a golf ball as it looped-the-loop. Would its speed match the predictions of the physics?

It was a pleasure to deliver workshops to schools including:
Corpus Christi Primary, Wellfield Middle, Stephenson Memorial Primary, Monkseaton Middle, Marden High, Burradon Community Primary, Southridge First, West Jesmond Primary, The Drive Community Primary and Usworth Colliery Primary.

We did not stop there, though. Oh, no. We ended the week with Physics in Perspective, a half-day of talks and discussions combining physics lectures and STEM careers information. We were delighted to welcome Professor Danielle George, a former pupil of Kenton School, who is now Professor in Microwave Communication Engineering at the University of Manchester and was the brilliant host of the 2014 Ri Christmas Lectures Sparks will Fly: How to Hack your Home. Danielle talked about the new rules of invention and showed participants how to use modern tools and technologies to have fun, transform everyday items and make a difference in the world. We were also joined by Northumbria University’s very own Dr. Rodrigo Ledesma-Aguilar who illustrated how nature has evolved some of the cleverest solutions to everyday problems by building “soft matter” structures. Exploration of these natural solutions is inspiring cutting-edge technological developments: bio-inspired smart materials.

We rounded off the day with a careers panel, where pupils had the opportunity to learn about the variety of pathways open those who study physics at A-Level, and to ask questions of the panel (Candace Adams from QuantuMDx, Paul Casson from Macaw Engineering and Danielle George).

Tomorrow’s Engineers EEP Robotic Challenge

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The Robotic Challenge is a curriculum-linked programme run by Tomorrow’s Engineers that sees students (11-14) working together in teams to solve real-world engineering, technology and computing challenges. Teamwork, robots, design, discovery, fun and loads of LEGO are all part of the mix, as are real-world challenges, teacher support and some great prizes.

Students learn how to build, program and control autonomous LEGO robots to complete a series of short, exciting space missions using LEGO® MINDSTORMS® Education EV3 sets. From assembling the crew to launching the satellite, they’ll demonstrate the skills they’ve learned at challenge events held around the country.

The journey starts in school. The challenge events are the culmination of a ten-week extra-curricular or in-school programme where students learn how to design and control their robots to complete the space challenges. Tomorrow’s Engineers will provide structured activity plans and learning software, training and equipment.

Activities can be run with your team outside the classroom or during lessons. The challenge could take your team all the way from regional heats to the national final!

Booking opens: April 2016
Visit robotics.tomorrowsengineers.org.uk/What-is-the-challenge/ for the latest information

Introducing the Technology Wishing Well for Maker Faire UK 2016

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At Maker Faire UK last year Think Physics had two stands; a wall of light boxes, and a magnificent harmonic pendulum display which, slightly embarrassingly, I still haven’t written up. Hoping to avoid a similar mistake this time around, I should introduce you to this year’s new installation: the Technology Wishing Well.

WishingWell v1

Er… yeah, that’s a bit of a mess. What you’re looking at is a corner of my desk, on which you can see the black disc of a small turntable. That’s part of the light box installation, repurposed shamelessly (hey, I’m allowed to steal from myself, right?). On the turntable are a couple of LED lights. The green one is pointing upwards, the red one fell over and is pointed off to one side.

Left of frame is a retort stand, holding a Raspberry Pi (Pi 3! Woohoo!) and a PiCamera, which as far as I can tell is a mobile phone camera module on the end of a stubby little cable. The Pi is driving the big monitor upper right, and the window in the top corner is showing… what, exactly?

OK, so I’ve written a little Python code which does the following:

  1. Grabs a picture from the camera.
  2. Takes all the stuff which is ‘dark’ in that image, and turns it transparent.
  3. Adds the result to the previous image.
  4. Repeat.

So, as the turntable turns the green light smears into a ring, and the fallen-over red light smears into a… weird red blobby donut thing. My python code is appallingly slow, but conveniently the result is mesmerising to watch as it gradually builds up. Which is a relief, because we’ve committed to building this thing and there’s no turning back now.

The plan is to build a big one of these, so the current turntables can sit on the big turntable, and then we’ve made a giant light-powered video Spirograph-like-thing. We’re also planning to build little gizmos which move lights around, or change their colour over time, or … well, you’ll have to wait and see. You’ll also be able to make your own lights and toss them onto the turntable disc to add to the artwork as it develops, which is where the whole ‘wishing well’ idea comes in.

There’s lots to do before Maker Faire, but right now I’m just excited (and a little relieved) to see something on a screen rather than in my imagination. This moment’s been a long time coming.

The header image shows the first run of the software – here’s detail of the second, just before the Pi crashed hard. Umm… I should probably look into what caused that.

Tech wishing well second run