Physics / Science

The physics of maple syrup and orange juice

It was a lazy Sunday morning and I had my favorite breakfast in front of me – Pancakes. I love the taste of pancakes with lots of maple syrup drizzled over it. I was very very hungry and eager to tuck in. I lifted the bottle of authentic Maple syrup and positioned it over the hot pancakes waiting for the maple syrup to fall and cover my yummy breakfast. Was I imagining it or was it for real? The maple syrup was in no hurry to leave the bottle. You can imagine its movement in slow motion – slowly and slowly flowing down to the neck of the glass bottle and then very slowly drawn out in time, the first drop makes its appearance at the mouth of the bottle and then trickles very slowly on to the pancake. I waited rather impatiently till it coated the pancake and started gobbling it up. Fortunately, I did not have to wait that long for the orange juice to fill my glass though. Now with my stomach comfortably full, I sat back on my bean bag to ponder over the mysterious behaviour of these liquids. Why did the syrup take so long to come out of the bottle while the orange juice was more than happy to leave the bottle and quench my thirst?

The answer to this question which many of us may have thought about is the property of liquids, called viscosity. Viscosity is the resistance which the molecules in the liquids have to flowing freely. This is mainly due to an internal friction between the molecules in the liquid. The more the resistance, the more the viscosity, hence viscous liquids like syrup, honey etc flow very slowly compared to less viscous liquids like water, clarified juices etc.

One way to make these viscous liquids run faster is by heating it. Upon increasing the temperature, the speed of the molecules in a liquid increase and they spend less time in contact with each other making them runnier and less viscous. On the contrary when you heat a gas, the molecules which were freely moving now hit against each other more frequently than before thereby increasing their contact time. This in turn decreases the coordinated movement of these molecules as a unit which makes them thicker or more viscous.

Viscosity is measured using many methods, one of which is based on using capillary tubes and measuring the time taken for a given volume of liquid to pass through a given length of the tube, mainly driven by gravity. This is called a capillary viscometer. Rheometers are devices that are used to measure the flow of liquids whose viscosities vary with external flow conditions.

The viscosity of water is around 1 millipascals.second.

So thus I deduced that it was no conspiracy against me by the syrup manufacturers but rather due to this physical property of liquids – Viscosity, which made me wait before the first trickle of maple syrup on my pancakes. Satisfied thus, I stood up contemplating a second round of breakfast (or should I call it brunch (?)). Let me bid adieu to you for now as I leave to have some more pancakes with highly viscous syrup accompanied with a glass of low viscous orange juice.

To read more on viscosity:

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