- Me: I need to get an A on this test
- Me: Doesn't study
No matter how long the slinky is, the bottom of the slinky will stay still (hover) until the top reaches it. Even if the slinky is over 1000 feet long.
not ‘no matter how long’… the material the slinky is made of matters, and the length too. you see, when you let a slinky hang from one end suspended, gravity is exerting force on the slinky while at the same time stretching out what is essentially a spring.
a string under pressure (even the pressure of gravity) stores that pressure in the form of heat energy to be released as kinetic energy when the pressure is released.
so when you drop the anchored upper end, gravity continues to exert pressure on the slinky in a downward motion at the same time that the stored energy is released. if you’d put the slinky on a horizontal surface and stretched it out, when you release both ends of the slinky (because to stretch a slinky on a horizontal surface you must either anchor one end while continuing to exert pressure on the other or divide the pressure evenly across each end) the slinky’s ends will each move towards the middle.
what you see in this gif is physics in action. gravity plus the stored energy in the slinky resulting in the illusion that the bottom of the slinky is hovering. it’s not hovering, it’s moving towards the middle of the slinky while falling downwards at exactly the same rate of speed.
if the slinky were made of different material or had a different length, the illusion wouldn’t hold, because the rate of contraction towards the middle wouldn’t match the rate of falling down due to gravity. both because materials move and act differently and because gravity isn’t constant at all elevations (so a mile long slinky would have different values of ‘g’, the ‘constant’ we think of as gravity, acting upon it at different points along it’s length.)
slinkys and physics are fun!