# What makes a bottle full of water soo bouncy?

Let's take a small coke bottle (a plastic one). Now fill the bottle entirely with water not even letting a small air bubble, however we cannot stop forming a tiny bubble. Now this water bottle when dropped will bounce of the floor as shown in the image.

I think that it became elastic due to the shock waves produced in water due to sudden impulse on the bottle.

However, if the air bubble inside the bottle is somewhat large then it would lose it bouncy nature. I don't know how these waves make this. Could you help me to understand the exact reason behind this?

Even the bouncy nature is dependent of configuration of fall. In the given figure if the bottle is allowed to leave at the below given configuration the bottle is not a bouncy one. How could you help me in understanding this phenomenon?

Also, I found an interesting fact about this. Not only this orientation, but also it depends on the stiffness of the material. I expected that when stiffness decreases then it will bounce more. But after observations on it, I got result that when stiffness increases then bouncy nature increases to a peak value then after increasing the stiffness the bouncy nature decreases. But why?

Why this phenomenon is seen in bottles with liquids but not gases? What if it is a solid!

I even found a new thing that bounciness also depend upon the length of the bottle. I had guessed that “The more spherical it is, the more bouncier it is”. That is length is inversely proportional to bounciness. Is this assumption correct?

• I got result that when stiffness increases then bouncy nature increases to a peak value then after increasing the stiffness the bouncy nature decreases - This is interesting, but how did you experimentally change the stiffness, take a bottle of thicker plastic? – Aleksey Druggist Oct 7 '19 at 10:49
• After observing that it has bouncy nature. I and my friends played with it for sometime. Then the bottle became softer, and bounced height also got reduced. But if I take a thick bottle intially, I didn't see any thing like before. – Sandesh Goli Oct 7 '19 at 10:58
• But also, great to get a reason for it. What might be the reason!!! – Sandesh Goli Oct 7 '19 at 10:59
• I'm not sure, but perhaps the whole thing is the viscosity of the water. A plastic bottle can be considered as a spring with a bending stiffness $k$, mass $m$ in the presence of damping force. If the stiffness is too high, the damping time when hitting the surface is short. The velocity components arising in the fluid upon hitting are higher and, accordingly, the internal friction (damping) is higher and the impact is inelastic with no bouncy. That is, a stiffer collision with the surface is less elastic – Aleksey Druggist Oct 7 '19 at 12:27