16 August 2012

Drink More …! Or Is Volume Actually 3D?

According to Geometry and Physics volume is three dimensional. The volume of a cube is equal to the length of one side at the third power. This is something that anyone that graduated from secondary school consciously knows. However, (human) perception of volume is not actually three dimensional. It is not even two dimensional. It is in fact one dimensional.

But which dimension is used to evaluate the volume of an object? Is it height, length or depth? The dimension used by people to evaluate volume is HEIGHT. The area (surface) of the base of an object is ignored and the volume is evaluated solely by the height of the object.

Imagine that there are two types of glasses available – tall and short – and all glasses have exactly the same volume. People who drink from tall glasses will drink less than people who drink from short ones. Now assume that people who drink from tall and respectively short glasses are equally thirsty. The people who drink from tall glasses will need to drink less to satisfy their thirst than people who drink from short ones. So it is not only the eye that gets fooled, but also the brain and body.

This is something that people working in bars have already learned from practice. Maybe you’ve already noticed (if you didn’t you will after reading this post) that in bars drinks are usually served in glasses that are tall and ridiculously narrow (Small area of the base). This is done to sell a small quantity at a bigger price.

Similarly companies that sell beverages have learned this and make the recipients with a very small base and as tall as possible. This “trick” is also used when companies decrease the volume in a packaging and want to keep the same (or a very close) price. Suddenly a bottle of 750ml looks very much like a 1000ml one, a 400ml bottle looks like a 500ml one and a can of 250ml looks bigger than a 330ml one.

The implications for decision design and behavior building are strait forward. For beverages that should be consumed with moderation (such as, of course, alcohol, particularly strong drinks) it is preferred to serve or consume them from tall glasses with a small base. On the other hand, for things that should be consumed in larger quantities (such as water), it is preferred to serve or consume them from short glasses with a large base.

Even if this is strait forward and bars and restaurants will soon use “test-tube like” glasses, the second implication is not used at all. If we think that particularly during hot summer days water is sold and served as in winter days it is a bit awkward. It is more the case to use these behavior building insights for large events that take place in open air at 30+ degrees in the burning sun or at beaches or for people that work in high temperature conditions such as construction workers. Even if by using short and “fat” recipients people will drink more (in actual volume) than they (perceive) need, this is not actually an issue since they will lose a lot of water due to the heat… 

Here's a nice example: One glass and one 300ml bottle of beer. Which one is bigger?

Now let's see when the beer was poured into the glass...

The entire content of the beer bottle (300 ml) was poured into the glass... The glass has a volume of a little above 330 ml. I can fit a 330 ml can of juice in it and still can drink it without spilling.

Enjoy your drink!

Later Edit: Here is a brief article on how the shape of a glass influences the speed of drinking beer (but not soft drinks). The key idea is that a curved glass does not make it easy to evaluate how much has been drank already, while a straight glass facilitates this evaluation. http://www.bbc.co.uk/news/health-19436926 Thank you Cornelia   

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