DIY Firestarters

Last week a listener told us you could use Twisties as firestarters.

Being a scientist I had to check it out of course. And while I was at it I thought I’d check out some other snacks.

So here’s the list:

  • Twisties
  • Chezels
  • Smiths chips
  • Burger rings
  • Woolworths rippled wholegrain chips
  • Chezels bacon boy rashers
  • Peanuts

The test was that I simply lit them and see how well they burnt.

Did the Twistie work? Yes it did, and as it burnt you could see the fat melting and running back down it.

In fact, they all pretty well worked OK, but there was one standout performer – the Chezel. It’s cylindrical shape meant that there was enough air flow to ensure highly efficient combustion, and in fact it was the only one that burnt completely.

So there you go – next time you go camping, pack the Chezels, just in case you forget the firestarters.

No one can say that I don’ttackle the big issues on this blog.



Science and the Olympics

Last night whilst watching the trampolining Liz Chetkovich noted that they now quote “time of flight” as one of the measurements that defines an athlete’s performance.

She then went on to say that this advantaged heavier athletes as they could depress the springs further when they landed, thus getting more push into the air.

Not quite right.

In layman’s terms, although the heavier athlete will indeed push the springs down further, the springs then have more weight to lift when they push him back into the air.

In fact, if you dropped two different weights onto a trampoline, and there were no energy losses in the system, and the springs obeyed Hooke’s Law perfectly, then both would bounce back into the air to exactly the same height from which they were dropped.

But of course there are energy losses in the system, and so they would not in reality rebound perfectly.

But the trampolinists of course continue to bounce high, and the reason simply is that they are putting energy into the system with their legs as they push off.

Thus the time of flight is determined not by the weight of the athletes, but by their power to weight ratio – their ability to generate the explosive power in their legs that will overcome gravity and push them higher into the air.

How to Make Your Own Toothpaste

I came across the recipe for making your own toothpaste.

The basic idea is sound, but I have a few suggestions that would improve upon this recipe.

Firstly, baking soda would probably be too abrasive, mostly because of the relatively large particle size.  And I don’t think that substituting salt in its place is a very good idea, beef only because it would taste terrible.

Want would be much better is alumina, which is what’s in commercial toothpaste anyway.  Alumina is aluminium oxide and is a very fine, free flowing white powder that is used to make abrasive pastes in many different industries, such as optical and jewellery.

It should be readily available from most chemical suppliers and shouldn’t cost much, which is the whole point of the exercise anyway.

But you will will still want some sodium bicarbonate (baking soda), in there, as it neutralises food acids.  Perhaps three parts alumina to 1 part bicarb is what you want.

But I’d go very easy on the hydrogen peroxide, as you won’t need much to burn your skin.  I’m not sure how many places sell it, but it’s available as a 50% solution from Tasman chemicals in Wangara, which is mighty strong. Make sure you take note of the safety instructions on the label.

As a starting point for toothpaste, I wouldn’t use it at any more than 1% (so a one in 50 dilution).

if you have a go at this, let me know how you get on.

A Neat Detergent Trick

Some time ago I described the nature of detergents, with particular emphasis on a neat demonstration you can do.

Well, someone has come up with an even better one.

To reiterate what I said before, detergents are surfactants, which is an abbreviation of surface active agent – so any detergent loves surfaces, and this is why they clean dishes – they go looking for any interface they can find – liquid/solid or liquid/air. So when the tiny drop of detergent touches the surface it spreads out along the surface, pushing the pepper out of the way.

Why Do Helium Balloons go Flat so Quickly?

When we blow up a balloon normally, they can stay inflated for a couple of days.  But we all know that helium balloons normally go flat within one day.


The answer comes when we consider what pressure is.  Put simply, pressure is caused by the gas molecules whizzing around inside the balloon and banging against the sides.  Each time they collide with the side of the balloon, they bounce off, but in doing so push the rubber out a little bit.

Now it makes sense to say that the heavier the molecule, the greater the impact when it hits the sides of the balloon, and therefore the more pressure it exerts.

Well, helium is a very small molecule, and air is much heavier, being composed mostly of nitrogen and oxygen.  In fact, the ratio of the weights of helium to air is about 7 to 1.  So the air molecules are about seven times as heavy as the helium.

But here’s the funny thing – according to the ideal gas law, a certain number of molecules of air under the same conditions will exert exactly the same amount of pressure as the same number of molecules of helium.

But how can that be?  If we have just seen that the air molecules are heavier, and exert more force, shouldn’t they cause more pressure if there is the same number of them?

Well, as it happens, there is one other factor that we must take into account – speed.  How fast are the molecules travelling?  Well, it turns out that the heavier air molecules are not moving as quickly as the helium molecules so although each impact exerts more force there aren’t as many impacts as there are fewer molecules.

On the other hand, the much lighter helium is moving far more quickly, and therefore colliding with the walls of the balloon more often.

And this is the simple reason why the balloons go flat – there are defects in the structure of rubber that allow the occasional gas molecule to escape.  Put simply, on a statistical basis alone, since the helium molecules are colliding more often with the walls of the balloon, they will escape more quickly.  So it’s purely a function of the frequency of their collisions with the sides of the balloon.  A statistical factor you might say.

Hydrogen, the other common lighter than air gas, is also a very small molecule, and would do the same as the helium (and probably quicker).