So how does the Slinky "walk" down a flight of stairs? To do this, the Slinky slowly flips end over end. If you watch closely, you'll see it stretches to reach the next step down, reforms itself, then stretches again to reach the next step, and so on. This process is possible because of gravity and the Slinky's own momentum. In this way a Slinky can walk down other surfaces, too, such as an inclined plane, which is a type of sloping surface that you will use in this activity.
Try to find one that's about two feet long by one foot wide, at least. This is the largest angle you will be testing. Using a protractor, measure the angle formed where the base of the plane meets the floor. Use the protractor to confirm the angle formed where the base of the plane meets the floor.
Let the lower part of the Slinky just barely touch the plane. This may mean that you are holding around half to two thirds of the Slinky's coils on the upper part of the plane. Why do you think you should hold the Slinky this way? Also count how many flips the Slinky does during this time.
Tip: Make sure the Slinky doesn't tumble down the plane but actually flips end over end; do not count any of the "walks" in which the Slinky tumbled. Write down your results. How long did it take in these other trials, and how many flips did it make?
Use the protractor to confirm this. Learn about nodes and antinodes of motion and compression. Hold the Slinky between your hands—it will be horizontal and will sag. Move both of your hands up and down together. Find the lowest frequency that produces the largest motion of the Slinky using the smallest motion of your hands this should be about one cycle per second. One large hump—half a wave—should appear, moving up and down on the Slinky see illustration below.
Count the rhythm every time the middle of the Slinky hits bottom—1, 2, 3, 4, 1, 2, 3, 4, etc. If you have trouble, try doing this same experiment using a side-to-side motion on a table top. Notice that the center portion of the Slinky moves up and down the most and the portions nearest your hands the least. Try moving your hands in opposite directions—that is, move the right hand up when the left hand moves down and vice versa. Move them in the same rhythm as above.
Notice that your hands move a large distance while the center of the Slinky hardly moves at all see illustration below. Again, if you have trouble, try this on a tabletop. When you move your hands together, you make a half a wave on the Slinky. The middle of the Slinky is an antinode , a point of maximum motion, while the hand-held ends are nearly but not quite nodes , points of no motion. When you move your hands in opposite directions, a half a wave also appears on the Slinky.
However, this half-wave has one node in the center and two antinodes near the hand-held ends. The timing on both of these is the same—that is, the period is the same. They both are resonances in which one half-wave fits onto the Slinky. Both of these patterns of motion have the fundamental frequency of oscillation, the lowest frequency of motion for a Slinky held at both ends—close to 1 hertz.
For the transverse motion of the Slinky, at places where the motion of the Slinky passes through zero a node of motion , the slope of the Slinky changes the most an antinode of slope.
So at the same spots where there are nodes of motion, there are antinodes of slope. Tie the fishing line to a chair. Slide the slinky onto the fishing line, and then tie the other end of the fishing line to another chair. Pull the chairs apart until the line is taut.
But the more stretched-out top would snap back faster toward the bottom, resulting in the same levitation time. As Kolkowitz pointed out, however, the Slinky's center of mass — which shifts, but is always located somewhere in between the top and bottom of the toy — still accelerates according to gravity all the way down to the ground from the moment it's released.
So there's no violation of any of Newton's laws or Galileo's observations about falling objects. The levitation time would only increase with a heavier Slinky and decrease if the coils were stiffer.
The spring's mass and stiffness, Kolkowitz said, are the only two factors that affect the duration of levitation. Kolkowitz pointed out this levitation effect would occur when any other spring or other elastic, nonrigid object is dropped -- and no object is completely rigid. Another way to think about the levitation problem is that "the wave velocity in that Slinky is all that matters," Kolkowitz said.
The wave velocity dictates "the length of time it takes information to reach the bottom of the Slinky," he said. Once that wave slams into the bottom, the bottom no longer levitates. In his analysis, Unruh observed that the collision of the upper part of the Slinky with the motionless lower coils is an example of a shock wave, analogous to a sonic boom that occurs in aircraft traveling faster than the speed of sound.
As the slinky moves down the steps, energy is transferred along its length in a longitudinal or compressional wave, which resembles a sound wave that travels through a substance by transferring a pulse of energy to the next molecule.
How quickly the wave moves depends on the spring constant and the mass of the metal. Other factors, such as the length of the slinky, the diameter of the coils and the height of the step must be considered to completely understand why a slinky moves as it does. James originally developed the Slinky for the Navy as an anti-vibration device for ship instruments. When the Slinky failed to work for the Navy, it became one of the most successful toys of all time!
Longitudinal Wave --A wave in which the vibration is in the same direction as that in which the wave is traveling, rather than at right angles to it. Sound waves are longitudinal waves. Transverse Wave --A wave in which the vibration is at right angles to the direction in which the wave is traveling. Waves in the stretched strings of musical instruments, upon the surfaces of liquids, and the electromagnetic waves which make up radio waves and light are transverse.
Inertia --A property, or quality, that tends to keep objects in motion in a straight line, or to keep objects at rest motionless, unless either one is acted upon by an outside force. Friction --The force that acts when two surfaces rub against each other. Friction always acts to slow movement and if no other force is applied, it will bring motion to a stop.
You can overcome an object's inertia and watch physical forces act on it as it moves.
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