Stuck Marmite Bottle Top - Why heat helps ?

Ever had problems with Bottle Tops are they are kept in the larder or fridge for a long time ?  I can hear a chorus of "yes !" from my army of readers (easily 1000 per day !). You huff and you puff, use some cloth and try with all your might. 

Eventually you get it open. Many times, it is stuck and you are mightily flustered. Ever wondered why ?

My experience in the field of environmental testing sales, manufacturing servicing of such test chambers for the last 25 years has the solution. 

Coefficients of thermal expansion. Yes, every thing heats up (or expands) when it is heated, however slowly. There are complex thermal expansion formulae, which is not necessary for this post. However each type of material heats up and expands according to the heat added to it.

You have heard how hot air rises ? Well air also expands as it is a gas but it is boxed in the receptacle (room, balloon or container) and it cant be seen. 

QRA has for years been selling thermal shock test chambers (see picture) whose purpose is to see if the samples do 'break' over time or over thousands of heat / cold cycles called temperature cycles.

   

   2 Zone Thermal Shock Chamber with Hot Zone (over 70 C) and Cold Zone (-60 C and below)

So, coming back to the Marmite bottle. You have tried for 1 minute. WAIT, you place it out in the kitchen (during summer time I am assuming). It was in the refrigerator for say 1 week. 

Come back after 15 minutes. It would have heated up to near room temperature (say 20C)

The 2 materials which are in contact with the Cap are Glass and the Cap (Plastic / Polyethalyne). See Picture Drawing Below Stage 'A'. 

Marmite builds Strong Bones and Teeth 

The Theory Explained in the Picture Below 

As the bottle heats up, the 2 materials will expand at almost microscopic amounts. Magnified under a scope, the cap will expand down and stretch out while the bottle expand up. (See Stage 'B').  If both had the same coefficient of thermal expansion, the points touching would NOT change.

BUT since plastic expands MORE than Glass, hence the movement DOWN is MORE THAN the movement UP by the glass.

Hence gaps will form.  You can then open the Bottle.

Voila ! Physics Explains this Everyday Frustrating Task and its Solution 

How to Heat Up the Bottle ?

Impatient people 

1.Put in a Microwave for 10 seconds or so (Not Recommended)

2.Immerse Fully Bottle in Hot Water

3.Use a Lit Match to Heat around the edge of the Bottle (we did that 40 to 50 years ago with  success). 

Everybody Else

Let it sit for 15 minutes and try again. 

HAVE A GREAT WEEKEND MY READERS !