How does the size + weight of slinkys affect their
walking speed going downwards
at 45 degree angle?
INTRODUCTION:
To a kid the slinky may be just a simple toy that just moves back and forth and is nice to occupy time with, but to physics students, like Liz and I, it is a phenomenon to be studied!! Yes, we're geeks! ; )
This web page will help you understand the phenomenon of physics of slinkys. What factors affect the slinky's speed as it goes down 5 steps of the graduated stack of books? What is being demonstrated when the Slinky is "walking" down the steps or an incline? Hmmm... You'll learn this further down the web page.
RESEARCH:
Before we started our experiment, we did some research on the internet about slinkys, how it relates to Physics and how the slinkys relate to what we are currently learning in Physics: waves and frequency. One web page, Slinky PHYSICS, had an experiment on how to find the slinky walking speed vs.. angle, but we decided to do an experiment on the slinky walking speed vs. size. All the information we used is listed on the "Links" section.
The essential features we will be researching is walking speed of the slinky and how size + mass affect its speed. We could've studied how the initial speed affect its ability to make the slinky down 5 books, but we did not know how to measure how fast the slinky would be released in the beginning.
With our research we confirmed the factors that will contribute to the slinky's movements:
momentum: the force of the slinky, when it is pushed, gives off momentum to keep it going down the books
longitudinal waves: as slinky goes down the steps, energy is transferred along its length in a longitudinal wave
compression: as slinky moves down the steps, it comes together before going down again
You can use a Slinky to get a good idea of how compressional waves, such as sound, move. Stretch a Slinky out and then give one a good strong knock or jiggle. This will push the coils near your hand into the ones next to them, which will be pushed into the next and next and so on, all the way to the other end. At the other end, the compression will rebound and move back in the other direction. Thus, a "compression" moves back and forth comparable to a sound wave and an echo. In sound waves, it is molecules of air that get pushed into each other, rather than coils of a spring, but it is the same concept. The sound waves move by pushing molecules forward in the direction of motion.
Source: Slinky Compression Wave
inertia: the slinky in motion stays in motion
potential energy: is demonstrated before the slinky makes the next flip down the book (or step)
kinetic energy: is demonstrated when the slinky is released downwards, kinetic energy comes after potential energy
After our thorough research, we predict that the smaller slinky will go down the graduated steps of books faster than the bigger (regular) size slinky. The reason we have come to this conclusion is because the smaller the mass, the tighter the tension; the tighter the tension, the faster the wave speed. (Teaching Tools) So as a result, the wave will move faster through the smaller slinky. In the next section we will try to prove that our hypothesis is correct or not.
PROCEDURE:
MATERIALS & what it will be used for:
5 books (or more to support the stack of books), all the same books or the same thickness (7 cm). The books will be used for the slinky to walk down because we realized the gym stairs were too big for the smaller slinkys to make it down to at least 2 steps.
Stopwatch, for timing how long it takes the slinky for it to finish "walking" down the books.
Ruler, to measure the total height of the books for the slinky to go down.
Slinkys of different size and weight. No need to explain why we need slinkys; if it's not obvious, have you read the title of this home page or the last section? Hmmm...
Rip Wrinkly, Jiggl-o, David, & Joe Mamma
By using the materials listed above, find the data by following the procedure:
1) Stack 5 books like stairs
2) Measure the height of the books
3) Put the slinky's one end on the top and the other end on the next step
4) While holding one end of the slinky, flip the end on the top of the books over to the next book
5) Time when the slinky is released to when it reaches the bottom
6) Record the time and repeat 1-5 four more times
We had several discarded trials because either the slinkys did not go down the steps or it went sideways and fell to the side. If this happens during this procedure, continue until it "walks" down successfully. It may be frustrating at first, because we know we were, but persevere! That is our motto: Perseverence will work! = ) (Did we mention we're geeks?)
=
Liz and Deb watching "Jiggl-o" slinky going down the books....................Liz watching "Rip Wrinkly" going down the books
DATA:
Height of the books: 7 cm per book, 35 cm total height
TRIALS WEIGHT |
1 |
2 |
3 |
4 |
5 |
| Slow David 47.11 g | 1.47 sec. |
1.31 sec. |
1.56 sec. |
1.69 sec. |
1.90 sec. |
| Rip Wrinkly 82.52 g | 1.50 sec. |
1.68 sec. |
1.68 sec. |
1.47 sec. |
1.56 sec. |
| Jiggl-o 74.61 g | 3.50 sec. |
2.44 sec. |
2.72 sec. |
2.84 sec. |
3.25 sec. |
| Joe Mamma 74.24 g | 3.79 sec. |
3.06 sec. |
3.32 sec. |
2.99 sec. |
3.29 sec. |
| SLINKYS | David | Rip Wrinkly | Jiggl-o | Joe Mamma |
| AVERAGE | 1.58 sec. | 1.57 sec. | 2.95 sec. | 3.29 sec. |
EXPLANATION OF DATA:
We took the weight of the slinkys to see if it affects its speed. Then we did 5 trials and found the average speed of the slinkys. The smaller slinkys had faster time than the regular size slinkys. The "Jiggl-o" took a second to compose itself together before moving down to the next step (shown below), while the "David" and "Rip Wrinkly" "hurried" themselves down the steps, without taking a second or so to compose themselves. It was difficult for the smaller slinkys to go down all 5 steps but "Jiggl-o" did not have trouble at all.
When we look at the average for the two small slinkys, we notice that "Rip Wrinkly," which has a bigger mass, is more speedier than "David." We had predicted that smaller the mass, the tighter the tension, resulting in a faster speed. The first part of our hypothesis is right (that small slinkys would go faster than regular size) but in the case of "David" vs. "Rip Wrinkly" the mass did not affect its speed. Also, "Jiggl-o" weigh a little bit more than "Joe Mamma" but it went faster. (Because of these datas, we had to figure out what affected the slinky's speed other than the size. Then Elizabeth figured, and Mr. Robinette suggested too, that its stretchiness might also be a factor. So we measured its stretchiness by measuring the slinkys' height before they are released and after they are released. First measure the height when the slinky is set on the table and record this as the starting height (first picture). For the released height measurement, hold the slinky down by the first "ring" and let it hang. Wait until the slinky stops bouncing and measure the length (second picture).
| David | Rip Wrinkly | Jiggl-o | Joe Mamma | |
| Starting height | 3.81 cm | 5.72 cm | 6.48 cm | 6.35 cm |
| Released height | 33.66 cm | 50.17 cm | 142.24 cm | 129.54 cm |
After finding the stretchiness of the slinkys, it showed that what we had predicted was correct; the mass was not a factor affecting the slinkys' speed but its stretchiness and size were. "Rip Wrinkly" stretched farther and went faster than "David" and "Jiggl-o" also stretched farther than "Joe Mamma" and it's time was faster. "Jiggl-o" stretched farther because "Joe Mamma" is metal and less elastic.
Graph of Stretchiness vs. speed--
Equation: f(x)= A*exp(B*x)
A= .566
B= .2497
Mean error= .231
CONCLUSION
The equation for the stretchiness vs. speed, f(x)= A*exp(B*x).
f(x) equals the average speed of the slinkys.
A and B equal the slope. When we changed the numbers for A and B, the curve line moved up and down.
X equals the elasticity of the slinkys.
Mean error was low, under one, even though our line did not connect through all the points.
Our results might have been a little off because there is always sources of errors. Human errors: not starting or stopping the stopwatch in time, our "steps" were a little crooked as you could tell from our pictures of the trial of the two slinkys, and measuring the slinky before it reaches its full length.
Reviewing what we have learned: Our hypothesis was the lighter and smaller the slinky, the faster it will go. That was not true in our case because "Rip Wrinkly" beat "David" even though it weighed twice as much as "David." But "Rip Wrinkly" did not have that great advance over "David," its average was just one second less. "Jiggl-o" went down the steps very well since it stretched 142.24 cm. The stretch of the slinkys affected its speed as it went down the steps because as it flipped to the next step, it could stretch more to be able to "walk" more smoothly and easily.
If we had more time, we would have studied the significance of angle vs. slinky's walking speed and compare it to our experiment size vs. walking speed. Or we could have put the two different experiments together, like if the stretchiness of a slinky affected its speed as it went down different degree of angles. And next time, we would probably manage our time better so that we could have gotten more slinkys to experiment with. Four slinkys were not really enough for good data or for testing this experiment where it relied on having a lot of slinkys.
LINKS:
Slinky
PHYSICS: By Bob Barrett.
I got the line (the one that says "Slinky
Homepage," right above the LINKS) of this web page from here. Also
from this web page, the diagrams of the wave movements and information about
slinky movements.
Teaching Tools A website that has several activities with the slinky, including "Racing Slinky" which is kind of like our experiment.
Created by Elizabeth Chan and Debora Ma (L to R) with the
help of Mr. Robinette (not shown), in his 7th period Physics class
June 1999
