Can a 747 take off from a conveyor belt runway?

This question is currently going round on Facebook; one of my friends posted it, I answered it, and a few hours later entered a lengthy and circular debate in the comments section.  Here, with more space than a Facebook comments section, I'd like to pose the question, answer it and then address some of the misconceptions.

Here's the question:  Imagine a 747 is sitting on a conveyor belt, as wide and long as a runway.  The conveyor belt is design to exactly match the speed of the wheels, moving in the opposite drection.  Can the plane take off?

Shared originally by Aviwxchasers.Com a news and media site from the US.

My friend shared the post, and answered, "No - there's no way to generate lift."
My original answer:  

"I think you're assuming that the 747 will be moving because its wheels are being driven. The forward thrust of the aircraft comes from its engines, not from making its wheels turn (like a car). So the engines push the aircraft forward and the wheels just slide and skid along the conveyor belt , while the engines push the aircraft to take-off speed. The wheels don't have to turn to allow the aircraft to move."

However, this wasn't deemed sufficient by some other commentators, who (to summarise) posted the following questions or objections.

1. The conveyer would counteract the forward movement produced by the engines' thrust.  The conveyor matches the speed of the wheels in the opposite direction, so there can be no forward motion.
2. Lift is created by air flow over the wings. It doesn't matter how much thrust you have , if doesn't generate airflow over the wing, it won't fly.
3. The method of propulsion should be irrelevant. If the speed of the conveyor matches the speed of the wheels in the opposite direction, there can be no forward motion.
4. Take the vehicle out of the equation, it's all about the wheels and the conveyor. The faster the wheels turn, the faster the conveyor goes. Stick anything you want on top of the wheels, the principles are the same. Newton's third law
5. Indeed it's not about the wheels it's about forward movement (thrust from the engine) needed to take off but that forward movement is being counteracted by the conveyer    

Here, I propose to look at these arguments individually and collectively, and explain why the points which are raised aren't sufficient to stop the aircraft from moving and taking off.

1.  The conveyor would counteract the forward movement produced by the engines' thrust.  The conveyoy matches the speed of the wheels in the opposite direction, so there can be no forward motion.

1A.  The conveyor will only stop the wheels' rotation from generating forward movement.  However, it is not the wheels which are being driven - this is not a car or a truck.  The forward movement of the plane is not a result of the wheels successfully pushing against the conveyor belt; the forward movement of the plane comes from the push of the engines.  The result is that the plane will move forwards (the engine pushes against the air flowing through it, the air pushes back - Newton's Third Law) and the wheels will spin and skid down the track.

It's not "The plane moves forwards because the wheels go round", it's, "The wheels go round because the plane goes forwards [over a surface which has sufficient friction] ."


2. Lift is created by air flow over the wings. It doesn't matter how much thrust you have , if doesn't generate airflow over the wing, it won't fly.

True.  But there is thrust, and it is generating airflow over the wing.  The conveyor belt does not have the ability to resist the movement of the plane, only to counteract the turning of the wheels.  

The plane can move forwards -even along the ground - without its wheels turning.  The engine isn't driving the wheels.

3.  The method of propulsion should be irrelevant. If the speed of the conveyor matches the speed of the wheels in the opposite direction, there can be no forward motion.
and 
4. Take the vehicle out of the equation, it's all about the wheels and the conveyor. The faster the wheels turn, the faster the conveyor goes. Stick anything you want on top of the wheels, the principles are the same. Newton's third law

3A and 4A.  Comment 3 was a response to my question, "What happens if we replace the 747 with a space rocket, aligned horizontally on the conveyor belt runway, on wheels?"  and the comment suggests a misunderstanding about what's causing the forward motion of the plane.  The thrust of a space rocket is completely independent of the any wheels (they normally fly fine without them) and the wheels will just get dragged along the conveyor belt, without turning. 

Yes, the faster the wheels turn, the faster the conveyor belt goes.  But the wheels don't have to turn for the plane to move (as I said in response to 2).  The conveyor belt does not have some property which prevents something from skidding along it, just from preventing any forward motion due to wheels turning on it. 

You can only take the vehicle out of the equation when you realise that the vehicle isn't a car, with the limitations that a car has.

Newton's third law applies to rotating wheels and conveyor belts.  It also applies to the aircraft engines and the air flowing through them, or to space rockets and the fuel burning inside them.  I wonder if the Starship Enterprise (on wheels) would have this problem?

5.  It's all about forward movement (thrust from the engine) needed to take off but that forward movement is being counteracted by the conveyer  

The forward movement is not counteracted by the conveyor.  The conveyor just stops rotating wheels from generating any forward movement.  But if the wheels aren't rotating (because they're not being driven, such as in a car) then there's no movement to resist.

In conclusion, I'd like to offer this video from "Mythbusters" which shows a light aircraft attempting to take off against a conveyor belt (which in this case is being pulled by a pickup truck to match the plane's speed).  To quote one of the engineers, "People just can't wrap their heads around the fact that the plane's engine drives the propellor, not the wheels."

Some other 'everyday maths' articles I've written:

A spreadsheet solution - the nearest point to the Red Arrows' flight path from my house
The Twelve Days of Christmas - summing triangle and square numbers
Why are manhole lids usually circular?
"BODMAS" puzzles - what's the fuss?

The Science of A Good Hypothesis

Good testing requires many things:  good design, good execution, good planning.  Most important is a good idea - or a good hypothesis, but many people jump into testing without a good reason for testing.  After all, testing is cool, it's capable of fixing all my online woes, and it'll produce huge improvements to my online sales, won't it?

I've talked before about good testing, and, "Let's test this and see if it works," is an example of poor test planning.  A good idea, backed up with evidence (data, or usability testing, or other valid evidence) is more likely to lead to a good result.  This is the basis of a hypothesis, and a good hypothesis is the basis of a good test.

What makes a good hypothesis?  What, and why.

According to Wiki Answers, a hypothesis is, "An educated guess about the cause of some observed (seen, noticed, or otherwise perceived) phenomena, and what seems most likely to happen and why. It is a more scientific method of guessing or assuming what is going to happen."

In simple, testing terms, a hypothesis states what you are going to test (or change) on a page, what the effect of the change will be, and why the effect will occur.  To put it another way, a hypothesis is an "If ... then... because..." statement.  "If I eat lots of chocolate, then I will run more slowly because I will put on weight."  Or, alternatively, "If I eat lots of chocolate, then I will run faster because I will have more energy." (I wish).

However, not all online tests are born equal, and you could probably place the majority of them into one of three groups, based on the strength of the original theory.  These are tests with a hypothesis, tests with a HIPPOthesis and tests with a hippiethesis.

Tests with a hypothesis

These are arguably the hardest tests to set up.  A good hypothesis will rely on the test analyst sitting down with data, evidence and experience (or two out of three) and working out what the data is saying.  For example, the 'what' could be that you're seeing a 93% drop-off between the cart and the first checkout page.   Why?  Well, the data shows that people are going back to the home page, or the product description page.  Why?  Well, because the call-to-action button to start checkout is probably not clear enough.  Or we aren't confirming the total cost to the customer.  Or the button is below the fold.

So, you need to change the page - and let's take the button issue as an example for our hypothesis.  People are not progressing from cart to checkout very well (only 7% proceed).  [We believe that] if we make the call to action button from cart to checkout bigger and move it above the fold, then more people will click it because it will be more visible.

There are many benefits of having a good hypothesis, and the first one is that it will tell you what to measure as the outcome of the test.  Here, it is clear that we will be measuring how many people move from cart to checkout.  The hypothesis says so.  "More people will click it" - the CTA button - so you know you're going to measure clicks and traffic moving from cart to checkout.  A good hypothesis will state after the word 'then' what the measurable outcome should be.

In my chocolate example above, it's clear that eating choclate will make me either run faster or slower, so I'll be measuring my running speed.  Neither hypothesis (the cart or the chocolate) has specified how big the change is.  If I knew how big the change was going to be, I wouldn't test.  Also, I haven't said how much more chocolate I'm going to eat, or how much faster I'll run, or how much bigger the CTA buttons should be, or how much more traffic I'll convert.  That's the next step - the test execution.  For now, the hypothesis is general enough to allow for the details to be decided later, but it frames the idea clearly and supports it with a reason why.  Of course, the hypothesis may give some indication of the detailed measurements - I might be looking at increasing my consumption of chocolate by 100 g (about 4 oz) per day, and measuring my running speed over 100 metres (about 100 yds) every week.

Tests with a HIPPOthesis

The HIPPO, for reference, is the HIghest Paid Person's Opinion (or sometimes just the HIghest Paid PersOn).  The boss.  The management.  Those who hold the budget control, who decide what's actionable, and who say what gets done.  And sometimes, what they say is that, "You will test this".  There's virtually no rationale, no data, no evidence or anything.  Just a hunch (or even a whim) from the boss, who has a new idea that he likes.  Perhaps he saw it on Amazon, or read about it in a blog, or his golf partner mentioned it on the course over the weekend.  Whatever - here's the idea, and it's your job to go and test it.

These tests are likely to be completely variable in their design.  They could be good ideas, bad ideas, mixed-up ideas or even amazing ideas.  If you're going to run the test, however, you'll have to work out (or define for yourself) what the underlying hypothesis is.  You'll also need to ask the HIPPO - very carefully - what the success metrics are.  Be prepared to pitch this question somewhere between, "So, what are you trying to test?" and "Are you sure this is a productive use of the highly skilled people that you have working for you?"  Any which way, you'll need the HIPPO to determine the success criteria, or agree to yours - in advance.  If you don't, you'll end up with a disastrous recipe being declared a technical winner because it (1) increased time on page, (2) increased time on site or (3) drove more traffic to the Contact Us page, none of which were the intended success criteria for the test, or were agreed up-front, and which may not be good things anyway.

If you have to have to run a test with a HIPPOthesis, then write your own hypothesis and identify the metrics you're going to examine.  You may also want to try and add one of your own recipes which you think will solve the apparent problem.  But at the very least, nail down the metrics...

Tests with a hippiethesis
Hippie:  noun
a person, especially of the late 1960s, who rejected established institutions and values and sought spontaneity, etc., etc.  Also hippy

The final type of test idea is a hippiethesis - laid back, not too concerned with details, spontaneous and putting forward an idea it because it looks good on paper.  "Let's test this because it's probably a good idea that will help improve site performance."  Not as bad as the 'Test this!" that drives a HIPPOthesis, but not fully-formed as a hypothesis, the hippiethesis is probably (and I'm guessing) the most common type of test.

Some examples of hippietheses:

"If we make the product images better, then we'll improve conversion."
"The data shows we need to fix our conversion funnel - let's make the buttons blue  instead of yellow."
"Let's copy Amazon because everybody knows they're the best online."

There's the basis of a good idea somewhere in there, but it's not quite finished.  A hippiethesis will tell you that the lack of a good idea is not a problem, buddy, let's just test it - testing is cool (groovy?), man!  The results will be awesome.  

There's a laid-back approach to the test (either deliberate or accidental), where the idea has not been thought through - either because "You don't need all that science stuff", or because the evidence to support a test is very flimsy or even non-existent.  Perhaps the test analyst didn't look for the evidence; perhaps he couldn't find any.  Maybe the evidence is mostly there somewhere because everybody knows about it, but isn't actually documented.  The danger here is that when you (or somebody else) start to analyse the results, you won't recall what you were testing for, what the main idea was or which metrics to look at.  You'll end up analysing without purpose, trying to prove that the test was a good idea (and you'll have to do that before you can work out what it was that you were actually trying to prove in the first place).The main difference between a hypothesis and hippiethesis is the WHY.  Online testing is a science, and scientists are curious people who ask why.  Web analyst Avinash Kaushik calls it the three levels of so what test.  If you can't get to something meaningful and useful, or in this case, testable and measureable, within three iterations of "Why?" then you're on the wrong track.  Hippies don't bother with 'why' - that's too organised, formal and part of the system; instead, they'll test because they can, and because - as I said, testing is groovy.

A good hypothesis:  IF, THEN, BECAUSE.

To wrap up:  a good hypothesis needs three things:  If (I make this change to the site) Then (I will expect this metric to improve) because (of a change in visitor behaviour that is linked to the change I made, based on evidence).

When there's no if:  you aren't making a change to the site, you're just expecting things to happen by themselves.  Crazy!  If you reconsider my chocolate hypothesis, without the if, you're left with, "I will run faster and I will have more energy".  Alternatively, "More people will click and we'll sell more."  Not a very common attitude in testing, and more likely to be found in over-optimistic entrepreneurs :-)

When there's no then:  If I eat more chocolate, I will have more energy.  So what?  And how will I measure this increased energy?  There are no metrics here.  Am I going to measure my heart rate, blood pressure, blood sugar level or body temperature??  In an online environment:  will this improve conversion, revenue, bounce rate, exit rate, time on page, time on site or average number of pages per visit?  I could measure any one of these and 'prove' the hypothesis.  At its worst, a hypothesis without a 'then' would read as badly as, "If we make the CTA bigger, [then we will move more people to cart], [because] more people will click." which becomes "If we make the CTA bigger, more people will click."  That's not a hypothesis, that's starting to state the absurdly obvious.

When there's no because:  If I eat more chocolate, then I will run faster.  Why?  Why will I run faster?  Will I run slower?  How can I run even faster?  There are metrics here (speed) but there's no reason why.  The science is missing, and there's no way I can actually learn anything from this and improve.  I will execute a one-off experiment and get a result, but I will be none the wiser about how it happened.  Was it the sugar in the chocolate?  Or the caffeine?

And finally, I should reiterate that an idea for a test doesn't have to be detailed, but it must be backed up by data (some, even if it's not great).  The more evidence the better:  think of a sliding scale from no evidence (could be a terrible idea), through to some evidence (a usability review, or a survey response, prior test result or some click-path analysis), through to multiple sources of evidence all pointing the same way - not just one or two data points, but a comprehensive case for change.  You might even have enough evidence to make a go-do recommendation (and remember, it's a successful outcome if your evidence is strong enough to prompt the business to make a change without testing).

Chemistry Dictionary: Adrenaline (epinephrine)

Adrenaline (epinephrine)

Adrenaline is a hormone, which is a chemical messenger in the body.  When the body is panicked, adrenaline is released into the bloodstream, and it acts on many parts of the body.  It tells the liver to release glucose (sugar) into the bloodstream; it tells the heart to pump faster, and tells the airways to open to get more air into the lungs and more oxygen into the bloodstream.  This is called the ‘fight or flight’ response, as the body prepares to respond to a perceived threat.

The shape of the adrenaline molecule fits into specific ‘receptors’, called adrenergic receptors, found on the cells in the heart, liver and lungs (and many other organs too), and when the adrenaline molecule fits into one of these receptors, it activates the receptor and tells the organs (through further messages) to respond in their own specific way.

Adrenaline was first artificially synthesised in 1904, and since then has become a common treatment for anaphylactic shock. It can be quickly administered to people showing signs of severe allergic reactions, and some people with known severe allergies carry epinephrine auto-injectors in case of an emergency.  Adrenaline is also one of the main drugs used to treat patients who have a low cardiac output — the amount of blood the heart pumps — and cardiac arrest. It can stimulate the muscle and increases the person's heart rate.

It's also a useful starting point for many drugs, because it has a wide range of effects on the body.  For example, its effect on the lungs means that a variation on adrenaline can be used to treat asthma.  One particularly successful drug is salbutamol, and the salbutamol molecule has a lot in common with adrenaline.

Adrenaline

Salbutamol

The differences between salbutamol and adrenaline make salmeterol more "specific" - in other words, salmeterol is designed (or adapted) to make it target just the soft tissue in the lungs and wind-pipe, and affect the heart less strongly.  If you think of adrenaline as a super key that can open many doors, than salbutamol is an adapted key that's only able to open some doors.


You may recall diagrams such as these from from school chemistry classes - chemicals and molecules being illustrated by a series of carbon, oxygen and hydrogen atoms joined together by little lines.  The manufacturers of pharmaceutical compounds pay very close attention to these diagrams.  After all, the difference between a successful drug and a dangerous, toxic or addictive one is often just a hydrogen atom here, a carbon atom there.  Any drug which is released and authorised for sale in the UK has gone through rigorous checking to ensure that it is effective and that any side effects are also known.  Adrenaline is an ideal starting point for drugs, given its widespread effect on the human body; however, it's possible to begin with other starting points, and look to achieve different effects.

Sadly, in the UK, there has recently been an explosion of compounds which mimic the effects of popular illegal drugs such as cocaine, ecstasy and cannabis, but are chemically different enough to avoid being illegal.  Keeping up with the new highs is difficult. Chemical compounds are effectively legal until they are banned, which means the UK Government has no choice but to be reactive once a chemical hits the market, and must move switfly to determine if it is legal.  A recent report from the European Monitoring Centre for Drugs and Drug Addiction, stated that one new legal high was being “discovered” every week in 2011. Additionally, the number of online shops offering at least one psychoactive substance rose from 314 in 2011 to 690 in 2012.

Chemistry moleculemolecule

Blood Sweat and Tears (GlaxoSmithKline)

It only seems fair that as GlaxoSmithKline (GSK) continue to produce ever more images for their anti-doping advertising campaign, that I should try to keep up with them.

Their latest and final range, "Blood, Sweat and Tears," now features with two Olympic gold medal winners, Beth Tweddle and Sophie Troiano.  GSK have even put them on their own Flickr site. They've drawn some criticism (in fact, the whole range has) for their inaccurate usage of chemistry, and in some cases, totally nonsensical chemistry in their advertising, but I'm still happy to keep parodying them, in an affectionate but not pedantic way.   Having said that, it does seem strange that a multinational chemical and pharmaceutical company hasn't bothered to display its scientific knowledge in its advertising, and has left the science to a group of non-scientific marketing folks.

It is worth pointing out that GSK is the Official Laboratory Services Provider for the London 2012 Olympic and Paralympic Games, but that they are not actually carrying out the testing - just providing the facilities. These labs, facilities and equipment are provided to enable expert analysts from King's College to independently operate a World Anti-Doping Agency (WADA) accredited laboratory during the Olympic Games.

After that brief aside, here is what will probably be my final poster, celebrating the vast majority of non-Olympians who also believe in training, running and playing sports in a doping-free environment.  It's meant to be humorous, not political, and I'm not trying to promote or discredit any manufacturers of anything in particular (such as 'high-energy' soft drinks).

Chemistry Advertising: GlaxoSmithKline Chemistry Again

I'd like to follow up on my previous post about how GlaxoSmithKline (GSK) have recently been promoting their anti-doping testing technology for the Olympic games.  They've done this with some very impressive 'chemistry' adverts featuring British athletes. 

 Now that the athletes are winning medals, they've changed the message to one about 'blood, sweat and tears', see below (taken from GSK's FB page) :

After my first set of chemistry images based on GlaxoSmithKline's advertis, I think it's only fair that I try to keep pace with these new developments, so I've produced a few more of my own.  They're designed to recognise those of us who aren't Olympic standard athletes, but who still believe in drug-free sports and improving our performances through hard work and practice.  What do you think?

Chemistry Advertising: Glaxo Smith Kline

A different slant on Chemistry cartoons this time.  I've recently noticed (with enjoyment) that GlaxoSmithKline (GSK) have recently been promoting their anti-doping testing technology for the Olympic games.  They've done this with some very impressive 'chemistry' adverts featuring British athletes (some of them medal winners).  GSK have put these on their Facebook page, and so I've borrowed them, and produced some of my own alternatives.


Mine aren't meant to be offensive, just comical parodies.  I'm not intending to criticise GSK, just borrow their 'chemical plus picture' motif.  I'm not even going to criticise the chemistry of the 'molecules' they've designed... I'm just going to smile and participate in the chemistry advertising as well.


Here are GSK's (taken from their FB page) :

And here, just to raise a smile for the 'every man' who also doesn't believe in taking drugs to enhance his performance, are mine.

What do you think?

Chemistry Apparatus Cartoon: The Boiling Tube

I realise that my series of Chemistry Apparatus Cartoons has a large number of tubes in it.  But, to be fair, chemistry is full of tubes.  This is the last one in my series - I have two more non-tubes to follow.  After the measuring cylinder, I thought it was time to go back to the tubes:  here he is - the boiling tube.

Next time?  I only have two more in the series (unless inspiration hits me again), but we're not scraping the bottom of the barrel yet!

So far, the series of Chemistry cartoons has included The Test Tube, The Side-Arm Test Tube, The Delivery Tube, the beaker and The Measuring Cylinder.  I do have a 'formal' Chemistry background (I completed a Natural Sciences degree at Cambridge University) and have also written some more serious articles on Chemistry, including how I transferred from Chemistry to a career in online web analytics.