- #1
DuncanM
- 98
- 2
Hi, folks.
I am looking for some help to understand the physics of a water pendulum (in fact, I don’t even know if my terminology is correct). It has been several years since I left school and my math/physics tools are rusty.
Here’s the set up:
Whenever I come back from the beach with a partially-empty soda pop bottle and balance it on the roof of my car, it always seems to oscillate back and forth and the oscillations grow until the bottle finally falls over. Now I am wondering why the oscillations grow; as far as I can tell, nothing nearby is feeding it energy (there is no railway, etc. nearby to create a resonance vibration. I am not touching it, breathing on it, etc.).
What I am now considering doing is creating a science project for my son (in elementary school) based on this phenomenom. The equipment is simple and inexpensive: a plastic 2 Litre pop bottle partially filled with water and set on a convex surface.
I was planning to tell my son the oscillations grow because the water keeps changing its center of gravity, much like a person adjusts their body position on a playground swing when they want to go higher.
But first, I want to make sure I am correct.
Do the water bottle’s oscillations, indeed, grow because of the changing center of gravity? Or is another force at work (i.e. - lunar/tidal, or some other force)?
Duncan
I am looking for some help to understand the physics of a water pendulum (in fact, I don’t even know if my terminology is correct). It has been several years since I left school and my math/physics tools are rusty.
Here’s the set up:
Whenever I come back from the beach with a partially-empty soda pop bottle and balance it on the roof of my car, it always seems to oscillate back and forth and the oscillations grow until the bottle finally falls over. Now I am wondering why the oscillations grow; as far as I can tell, nothing nearby is feeding it energy (there is no railway, etc. nearby to create a resonance vibration. I am not touching it, breathing on it, etc.).
What I am now considering doing is creating a science project for my son (in elementary school) based on this phenomenom. The equipment is simple and inexpensive: a plastic 2 Litre pop bottle partially filled with water and set on a convex surface.
I was planning to tell my son the oscillations grow because the water keeps changing its center of gravity, much like a person adjusts their body position on a playground swing when they want to go higher.
But first, I want to make sure I am correct.
Do the water bottle’s oscillations, indeed, grow because of the changing center of gravity? Or is another force at work (i.e. - lunar/tidal, or some other force)?
Duncan