The physics behind an Ice-Popsicle not falling off the stick.
A colourful Ice-Popsicle (Ice-Gola in Hindi)
When I eat an Ice-Popsicle (which we call as Ice-Gola in Hindi) with someone and ask the question:
Why does the ice stay still on the stick without just falling off?
Either he/she is confused and doesn’t know the answer or I get the reason “The shredded pieces of ice don’t move because of friction between surrounding ice particles” as an answer.
And then… to blow his/her mind, I tell that the reason behind this is a phenomenon in physics called Regelation.
But hey, I just don’t leave after blowing minds.
I explain the mechanism properly after that.
(To explode minds).
Lol.
Before knowing about the phenomenon, you should know this fact:
When we apply pressure on the ice, its melting point decreases.
- I will explain Regelation with an example:
I take an ice block, which is frozen at the room temperature. Then I apply some pressure on it. We know that the melting point of ice is 0°C.
This value of melting point decreases for the ice (of the ice block) near the area where the pressure is applied (say -1°C). So, this part of the ice block starts melting.
Now, I remove the pressure. The value of the melting point of ice is restored back to 0°C. So, the ice (which was melted to liquid water due to a decrease in melting point) is frozen back.
We call this phenomenon as Regelation.
Coming to the making of Ice-Popsicle.
The person (who makes it) takes an ice slab and shreds it into fine ice particles using a shredding machine.
Ice-shredding machine
Then he takes the shredded ice and puts it inside a frustum shaped object made of a non-crystalline transparent amorphous solid (i.e. a cup of glass).
After that, he puts a thin stick inside the cup and compresses the ice hard.
Once the shredded ice is compressed for long, all of the tiny ice particles exert pressure on surrounding particles.
To understand what goes on at the microscopic level, consider a pressurized contact between any two ice particles:
When the person compresses the shredded ice, a resultant pressure is created between neighbouring ice particles at the microscopic level.
For the two ice particles, this pressure decreases the melting point of ice present near their surface of contact. So, this part of both ice particles melts and forms liquid water, which is stuck between their surfaces of contact.
On releasing the pressure, this layer of liquid water is frozen back to ice.
As a result, the two ice particles are attached.
Similarly, all of the neighbouring ice particles inside the shredded ice (all around the thin stick) are attached to each other by forming a strong bond.
And finally, the compressed shredded ice becomes a single object, which is attached to a stick.