Different Types of Metal Slinky Drops

These drops were recorded using a Canon Optura digital camera. The higher image resolution of this camera will allow motion to be seen in greater detail than in the plastic slinky drops.

The metal slinky has 90 coils, compared to the 39 coils of the plastic slinky. Its inner and outer radii are smaller than those of the plastic slinky, and each individual coil has a smaller surface area than individual plastic slinky coils.

The metal slinky is heavier, longer, and has less surface area per coil than the plastic slinky. Whereas the plastic slinky experiences a greater drag force, the metal slinky should experience less drag due to its smaller overall surface area. This lower drag force will allow the metal slinky to accelerate more closely to g than the plastic slinky is accelerated) and to fall more uniformly without rotating too far into the horizontal plane.

Questions to investigate with the metal slinky:

• Does the number of coils held before release change the motion of the slinky? This question was asked because when coils are held, the location of the center of mass of the slinky is changed, and this may produce changes in the slinky's motion upon release. Is there a number of coils for which the bottom of the slinky does move before the top reaches it?

• While dropping the plastic slinky, an interesting observation was made. It appeared that the top end of the slinky was falling faster than it would if accelerated by gravity alone. With the metal slinky, the rate of the top end's fall was investigated. With the plastic slinky, if one coil is held, the top end falls faster than g. When one coil of the metal slinky is held, the top end also appears to fall faster than g. Can the acceleration of the top end be changed by changing the number of coils that are held before release?

• To investigate this second question, a baseball, with roughly the same radius of the metal slinky (but not the same surface area) was placed on top of the slinky. The slinky was released with the baseball on top to see which fell faster. Different numbers of coils were held during each of these baseball drops to determine if changing the location of the slinky's center of mass had any effect on the acceleration of the top end.

• As another method of investigating this question, the slinky was positioned next to the baseball and dropped from roughly the same height as the baseball. This method offers a different way of comparing the acceleration of the baseball and the top end of the slinky.