Slinky!!

Everybody as a little kid loves to play with a slinky. Even as an older kid or adult, they all grab our attention. I have to admit, they are pretty fun to play with. They "walk" down the stairs, get tangled up, and captivate our attention. But, how do they actually work?

The slinky was created in the 1940s by an engineer who thought nobody would buy it because of it's simplicity. A slinky, like all objects, tends to resist change in its motion. Because of this inertia, if it were placed at the top of the stairs it would stay at rest without moving at all. At this point it has potential or stored energy. But once it is started down the stairs and gravity affects it, the potential energy is converted to the energy of motion or kinetic energy and the Slinky gracefully tumbles coil by coil down the stairs. When you drop a slinky, the bottom stops falling once it hits the floor and the top appears to be levitating while it continues to fall. The explanation for this comes from Hooke's Law.

Along with Hooke's Law, the slinky also provides insight into many different physics topics. These topics include equilibrium and energy transfer. The slinky shows stable equilibrium. Stable equilibrium is an object in this state will return to its original position when it undergoes a small movement or displacement. If you move the slinky, it will flip over and return to its original position. The slinky also shows the principal of conversation of energy. The conversation of energy is the total energy in a conservative system at two different times or positions is the same. This means that when the slinky is moving, there is potential energy and kinetic energy that equal the total potential energy of the system. When the object is at rest, there is the total potential energy of the system. In addition, the slinky also shows the conversation of momentum. The conservation of momentum is the momentum of a conservative system at two different times in the same when there is zero external forces acting on the system. Once the slinky is in motion, there are no external forces acting upon it. This demonstrates the conservation of momentum. All three of these principals are shown when the slinky is "walking" down the stairs.

When a slinky is placed at the top of a flight of stairs or a stack of books, it will remain in a state of equilibrium. This is because the slinky is not moving. Once an outside force moves the slinky, it will begin to "walk" downwards. When the slinky is at the top of the stairs, will have potential energy stored in it due to its mass being at an elevated position. Once the slinky is tipped over the edge, the potential energy is converted to kinetic energy as the slinky moves down the steps. This transformation of energy, from potential to kinetic, is the reason that the slinky can "walk" down the stairs. 

The moving slinky also has momentum as it moves down the first step. As it reaches the first step, the momentum is conserved and travels back the opposite direction. This causes the slinky to tip over and continue "walking" down the stairs. However, due to friction, the slinky stops going down the stairs after only a couple. In the perfect situation with no friction, the slinky would continue "walking" until it finished all of the stairs. 

Sources:

http://www.reachoutmichigan.org/funexperiments/agesubject/lessons/newton/slink.html

https://schoolworkhelper.net/the-physics-of-a-slinky-hookes-law/

http://www.mace.manchester.ac.uk/project/teaching/civil/structuralconcepts/StudentCoursework/contents/52.pdf