The Doppler Effect

You know that noise a siren makes as it goes whizzing past atop of an ambulance or police car? As it approaches you the pitch of the siren changes. This is due to something we call the Doppler effect. But you don't have to wait for an emergency vehicle to hear it in action...

 All you need is:

• A length of string
• A kitchen timer

What to do:

1) Securely tie the string to the timer (Double check this, you don't want the timer flying around later)

2) Start the timer beeping.

3) Find a nice big open space and swing the timer round your head in a big circle.

Notice anything odd about the sound of the beeper?

Well you shouldn't, because if you are doing the swinging then the distance between you and the timer isn't changing, so you won't hear a change in pitch. Just like you wouldn't notice the sound of the siren changing if you were sitting in the emergency vehicle. 

However if you get someone else to listen (watch out they don't get hit by) , then they'll hear a different note depending on whether the timer is coming towards them or swinging away.

What's going on?
Sound travels as waves, and the pitch of note depends on how close together the peaks of these waves are. So a high note will be made of waves with peaks that are closer together that a low note.

The timer is emitting a constant  beep with a constant note i.e. the distance between the peaks of the waves are always the same. But when the timer is travelling towards an listener (i.e. not the person doing the spinning) each wave peak is emitted from a point that is closer to the listener than the previous peak.   Therefore the time between each peak arriving at the listener is reduced and so the note sounds higher. Then the reverse happens when the timer is moving away from the listener and the note sounds lower.

And of course the person doing the spinning doesn't notice any change because the distance between him and the timer doesn't change.

Garlic Challenge, the results show!

In my last post I posed a question: Does rubbing your hands on stainless steel gets rid of garlic smells? There's clearly plenty who believe it does, you can even buy stainless steel 'soap' .

Various theories as to how steel may achieve this were posited. But I wanted to know if there was a real effect in the first place.

Kitchen chemists everywhere helped answer this by taking part in a stinky citizen science challenge. And the results are, well, interesting.

I asked people to conduct a quick experiment whilst prepping dinner. The task was simply to rub the palms of their hands with garlic. Then treat one hand with a wipe from a stainless steel spoon and the other with a wooden spoon. Finally participants asked some other poor soul to take a sniff of their hands and report on whether there was a discernible difference. Thanks to everyone who took up the garlic challenge (especially the person who did their experimenting whilst cooking Christmas dinner).

And so to the results. These were collected via surveymonkey, with the question "Which hand smelt more of garlic?" and the answer choices a) The hand rubbed with the wooden spoon, b) The hand rubbed with the stainless steel spoon, c) Couldn't tell the difference. 44 allium lovers responded. Of those 17 thought the hand treated with the wooden spoon smelt more garlicky, 6 said the stainless steel treated hand was the stinkier. So far, so good. Looks like the stainless steel effect might be real. But here's the rub, there's still the other 21 responses, none of whom could tell the difference between the smelly hands.  

So we've got results that are significantly different from an even distribution between the options (the two-tailed P value equals 0.0163 ,according to a chi squared test). However, the stainless steel treatment seems to be only about 38% effective, assuming the wooden spoon is a good negative control. But maybe the abrasive, absorbent wooden spoon is also quite good at removing garlic smells? In which case the effectiveness of the stainless steel is an underestimate. Oh well, sorry people, but it looks like I can't really offer a definitive answer. In hind sight I think the experimental design could have been better. A before and after spoon treatment sniff test would have been a good idea. And maybe a better negative control was in order. Is another round of experiments could be in order?

Does stainless steel get rid of garlic smells?

This morning a tweet caught my eye

OK a chemistry question for @FunSizeSuze stainless steel seems to get rid of garlic odour from hands, but how? http://t.co/aFPDOJQ48q
— Dr Suzie Sheehy (@suziesheehy) October 15, 2013

Speculation followed.

@suziesheehy Good question! From memory, garlic odour comes from allyl methyl sulfides. Presumably the sulfide part reacts with a component
— Dr Suze Kundu (@FunSizeSuze) October 15, 2013

But before we get to the 'how' question maybe we should figure our if there is any truth in the anecdotes.

So how about an experiment? And I'll be needing your help for this one.

You'll need

• A clove of garlic.
• A knife.
• A timer.
• A wooden spoon and a stainless steel table spoon of about the same size.

What to do
1. Wash and dry your hands (so they don't smell of anything to start with).

2. Cut the clove of garlic in half (don't peel it, that way your fingers won't pick up garlic smells when you hold it).

4. Rub the freshly cut surface on the palm of one hand for 10 seconds (use the timer).

5. Rub the second piece of garlic on the palm of your other hand for 10 seconds (this way each hand gets rubbed with a fresh piece of garlic of the same size).

6. Rub one palm with the back of the stainless steel spoon and the other palm with the wooden spoon (the wooden spoon is our control experiment). Again for 10 seconds each. Make sure you remember which hand was rubbed with which spoon.

7. Find a willing volunteer, ask them to close their eyes (with their eyes closed they are less likely to notice any signals from you about which hand has had what treatment).

8. Hold a hand under their chin (that way each hand will be the same distance from the test subjects nose) and ask them to smell it. Then do the same with the other hand.

8. Ask them which hand smelt stronger of garlic.

9. Let me know the results using the survey below. We'll need plenty of tests if we are going to be sure of our results, otherwise it's just more anecdotes.

I'll  get back to you with a conclusion when enough results are in.

Create your free online surveys with SurveyMonkey , the world's leading questionnaire tool.

The Underground Map of the Elements

If anyone wants a high res copy feel free to download it here.

Full story over at the Guardian.

And now available in mousemat, poster and mug form!

The Underground map of the elements Mousepad

The Underground map of the Elements Poster

The Underground map of the Elements Mugs

How to turn chlorophyll red

What colour is chlorophyll? Obviously its green. After all chlorophyll is the pigment in leaves that absorbs the Sun's rays in the first step of photosynthesis. It reflects the green light which is why the leaves are that colour. But what colour is chlorophyll under UV light?

You'll need.

• Some green leaves, spinach works well.
• A pestle and mortar
• A clear spirit like gin or vodka (best to ask an adult before using this)
• An ultra violet torch 
• A glass 
• Some kitchen roll

What to do.

1. Put a few leaves in the mortar.
2. Pour in about 20ml of gin
   
   
   
3. Gently mash it all up with the pestle until the chlorophyll dissolves in the alcohol and the liquid goes green.
4. Filter the bits out of the chlorophyll extract by pouring it through some kitchen roll and into a glass.
   
   
   
5. Now shine the UV light through your green liquid. You'll notice that where the UV light passes through the chlorophyll extract a reddish light is emitted. 
   
   
   
   
   
   
   
   
   
   What's going on?
   Chlorophyll fluoresces, this means that it absorbs light of one colour and emits it as another. So in this case the UV light gets converted into red light by the chlorophyll. You wouldn't notice this effect in leaves because the chlorophyll is bound up with a huge amount of protein machinery that the plant needs for photosynthesis. These proteins take the energy emitted by the chlorophyll and pipe it into complex pathways that result in the plants using the suns energy to grow. But strip away the proteins, using some alcohol, and that energy gets emitted as red light instead.

Dear all, it's a parody.

My Guardian post is meant as a parody of the Buzzfeeds article that I linked to at the top of the piece. I thought it was explicit enough to make that clear, however this doesn't appear to be the case.

My only intent was to show how, with the wrong spin, you can make anything sound dangerous.

So in case things still aren't clear.

1) E290 is just carbon dioxide. We breath it out all the time and is safe to consume in foods.

2) 8-methyl-N-vannillyl-6-noneamide is also know as capsaicin. It generates the 'heat' in chilli peppers and spice food. Riot police also use it a tear gas.

3) Denatured proteins in eggs don't cause any diseases.

4) DHMO or dihydrogen monoxide is just water

5) NaCl, as many have pointed out is table salt. The fact that both sodium and chlorine are dangerous is irrelevant.

6) And uranium oxide has long been used to make green glass. It too is perfectly safe.

Fancy some uranium?

Now, how about that uranium!

You can get hold of it really quite easily and better still it really does glow in the dark!

I'm actually talking about uranium oxide, not the metal itself. And you find it in some green glassware, were it gives a lovely minty colour. You might even have some at home without realising it.

Its easy to check if green glass contains uranium oxide because it fluoresces under UV light. Here's a bowl I bought for £5 under normal light and then under UV.

If you want to hunt some of this really cool (and slightly radioactive) glassware out then get yourself an ultra violet keyring torch and check out  green glass you come across in carboot sales, charity shops and antique markets.

Safety:
Fear not, uranium glass is safe. In fact when I ran a Geiger counter over this piece I couldn't measure anything above background radiation levels.

There may be a mild concern if you happen to have a large collection. But a small number of pieces is certainly nothing to worry about.

P.S. The ratio of uranium and oxygen in uranium oxides follows Fibonacci ratios i.e.  U₂O₅, U₃O₈, U₅O₁₃, U₈O₂₁, U₁₃O₃₄ ! Anyone care to explain why?