The Physics of Slinky Tricks: The Spring Constant, and How to Adjust It

In this post I'll explain why HyperSprings may dangle at different lengths, how that will affect they way they move for tricks, and why and how you may wish to adjust that by breaking off a few coils. First, it's important to understand what the spring constant is. 

The Spring Constant Explained

When held from the very end and allowed to dangle freely under the force of gravity, and once it stops bouncing up and down, the distance that a HyperSpring (or Slinky, or any spring toy) dangles at is proportional to its spring constant. This is a fancy physics term which basically equates to how stiff a spring is. 

Higher spring constant = more stiff. More force is required to stretch it out.

Lower spring constant = more loose. Less force is required to stretch it out.

The spring constant (k) is defined in the above equation: k = F/x. This is derived from Hooke's Law, as laid out by British physicist Robert Hooke in 1676.

Looking at this equation, we can assume that F (the force of gravity applied to the spring) is constant, and draw the conclusion that the greater x (the dangle distance) is, the lower the spring constant is. 

Thus, a spring with a higher spring constant won't dangle as far. 

A spring with a lower spring constant will dangle further. 

Two toy springs dangling freely under gravity. The one on the left has a higher spring constant, and thus doesn't dangle as far. 

The spring constant is not just important for physicists: it's extremely important to understand for those of us that enjoy the art of springbending / slinky manipulation / slinky juggling / slinky tricks (whatever you want to call it - it's a young art form and the jury is still out).

The spring constant is the main thing that determines how a spring toy will want to move, and what tricks are possible with it. 

Some springbenders think that counting the number of coils in a spring is the best metric for determining what tricks are possible with it. However, this assumes that the coils are the same thickness/density between springs, which is not at all the case.

I believe that measuring the dangle distance (under equilibrium, where it isn't bouncing up and down) is a much better way to get a rough sense of a spring's spring constant, and thus determine what tricks are possible with it. 

How the Spring Constant Affects Tricks

Springbending tricks are rhythmic. They are based on creating resonance: a single, powerful wave of tension that travels back and forth through the spring. The most basic form of this is the trick called the Basic Energy Beam. 

Thus, each spring has one rhythm that it naturally wants to move at. In physics terms, this is its natural frequency.  

(This is assuming that we don't change the number of coils we're gripping in each hand. Gripping more coils will decrease the number of coils a wave has to travel through from end to end, and speed up its natural frequency). 

The natural frequency is the rhythm at which you tug on each end when performing a Basic Energy Beam. 

Importantly, the natural frequency is proportional to the spring constant. What this means for you as a springbender is:

A spring with a higher spring constant (more stiff) will want to move at a faster rhythm, and in a shorter path through the air.

A spring with a lower spring constant (more loose) will want to move at a slower rhythm, and in a longer path through the air. 

These days, toy springs come in every different shape and size imaginable, all with wildly different spring constants. Most of them are not within the spring constant "sweet spot" for performing the widest variety of tricks. 

Luckily, the two main fundamental tricks that almost all other tricks are built upon, the Basic Energy Beam and The Basic Bounce, can be performed with almost any toy spring, no matter its spring constant.

(Though I highly recommend against any Slinky brand metal slinky, due to their inflexibility. Even the most basic tricks will permanently kink them in seconds. I also do not recommend the Slinky brand "Neon Slinky", as their coils are too thin and wide, which creates instability.)

For more advanced tricks, there is a more narrow range of spring constants that are ideal, and certain types of tricks may be easier with a slightly higher or lower spring constant. 

The tricks I call Flips, where the spring is tossed into the air and allowed to rotate end over end, are generally easier with a higher spring constant. This is because a spring with a higher spring constant will rotate end over end at a faster rhythm, and thus won't have to be tossed as high into the air to complete a single rotation. 

The tricks I call Twists, where the coils are manipulated into twisting shapes that appear to freeze back and forth in the air, will generally be easier with a somewhat lower spring constant. This is because the slower rhythm gives the user more time to complete each twist. 

Twists are an advanced form of Energy Beam. As such, the Basic Energy Beam will also probably be easier for beginners to learn with a slightly lower spring constant, because they will be able to move their hands with a slightly slower rhythm. 

Why Your HyperSprings May Dangle at Different Lengths

I've designed The Original HyperSpring and The Bigger HyperSpring to be well within the ideal range where all springbending tricks are possible. And actually, their spring constants are designed to be on the lower end of that range, with a little bit of extra length as a buffer. Allow me to explain why:

As part of my mission to become the #1 most trusted source for toy springs on the planet, I strive for perfect consistency in HyperSprings' spring constant, so you always know what you're getting. 

However, perfect consistency is extremely hard to achieve during the production process. Tiny variations in coil thickness/density will lead to noticeable differences in spring constant, and how it moves for tricks. 

This is why if you purchase two Original HyperSprings, they may dangle at slightly different lengths. 

Rest assured, even if one seems more "loose" (a slightly lower spring constant), they are still both capable of all tricks, beginner through advanced. 

If you have any doubts about this and think you might have received a dud, please email us an image of your spring along with its measurements (diameter and length) in the compressed position (not dangling), and its weight in grams, to info@hyperspringtoys.com, and we'll investigate. 

Furthermore, a few coils can easily be removed to increase the spring constant and make it feel more "stiff" if desired. I'll teach you how to do this in a moment. 

However, coils can never be added back on to decrease the spring constant. You can try this with duct tape, super glue, or whatever else if you don't believe me, but the joint will always be a weak spot where the wave does not pass through the coils properly. 

Because there will always be some variation in spring constant, and because coils can always be removed but never added back on, it is better to err on the side of them being too long. If your spring has a higher spring constant than you'd like, there is no way to fix this. But if your spring has a lower spring constant than you'd like, this can easily be fixed by removing coils. 

This is why in late 2024 I decided to have all Original HyperSprings come with an extra centimeter of length from now on. They will be 10 centimeters in length going forward. Some of you who purchased one in 2024 may already have one that is 10 centimeters in length.

Thus, if you prefer a slightly lower spring constant for learning Energy Beam Twists, you're good to go. And if you prefer a slightly higher spring constant for Flips, just remove a few coils and you're also good to go.

(As of January 2025, the Original HyperSprings I have left are still the old shorter 9 cm length, but when I restock in April, they will all be 10 cm in length, the same length as The Bigger HyperSpring.)

Why You Shouldn't Remove Coils

Before we get to how to remove coils, a disclaimer:

I do not recommend total beginners to remove any coils from their HyperSpring, at least until they've perfectly mastered the Basic Energy Beam and Basic Bounce. There are a few reasons for this:

1. The Basic Energy Beam will probably be easier to learn with a lower spring constant, since you won't have to move your hands at as fast of a rhythm. 
   
   
2. A lower spring constant will make your HyperSpring better at walking down stairs, if that's something you care about.
   
   (Though, stair walking is the least fun thing you can do with a HyperSpring. Check out the free Fundamentals of HyperSpring Video Course to learn 10 way cooler tricks you can do anywhere.)
   
   
3. After many hours of advanced use, a few coils will naturally break off the end of your HyperSpring anyway. 

Yes, unfortunately nothing lasts forever, HyperSprings included.

Practicing advanced moves like Twists puts a high level of tension into your HyperSpring, creating invisible micro-fractures near where you grip it, eventually leading to a few coils snapping off near the end.

Practicing in cold temperatures may accelerate this breakdown, while practicing in warmer temperatures may make your HyperSpring last longer.

Don't forget though that your HyperSpring is guaranteed to last at least 60 days from when you receive it, per the HyperSpring Guarantee. If it snaps before then, reach out to us at info@hyperspringtoys.com to request a free replacement. 

⚠️ If and when your HyperSpring snaps, the snapped end will be sharp. Be sure to sand it down on any piece of concrete or brick to make it safe for continued use. This only takes a few seconds. 

Once your HyperSpring snaps, you can enjoy the new higher spring constant, which will make Flips easier. Eventually it will snap again, and you can keep challenging your skills with a higher and higher spring constant until you can't use it anymore.  

How to Remove Coils to Increase the Spring Constant

If you've already mastered the Energy Beam and the Bounce, and you're sure you want to remove some coils without waiting for them to break off naturally, this is how you do it:

1. Pick a spot no more than 2 coils from the end. Remember, you can always remove more coils, but you can never add them back on, so I recommend removing no more than 2 coils at a time and testing the new rhythm after each break. 
   
   
2. Bend the plastic extremely back and forth on itself at that point about 20 times, like you're creasing a piece of paper. This weakens the plastic.
   
   
   
   
   
3. Twist the plastic continuously in one direction at this point over and over, like you're twisting off the stem of an apple. The coils will break off. 
   
   
   
   
   
4. If the end isn't smooth, sand it down by forcefully rubbing it back and forth on a piece of concrete a few times. Throw away the resulting plastic piece. 
   
   
5. Do an Energy Beam or other tricks for a few minutes to test the new faster rhythm. Repeat these steps if you want an even higher spring constant. 

That's it! You now know how to customize your spring constant like a pro. 

If you haven't yet, be sure to check out the FREE Fundamentals of HyperSpring Video Course to learn 10 beginner tricks that will turn your HyperSpring into an endless source of fun and fulfillment.

And if you've mastered at least the Basic Energy Beam, Basic Bounce, and Ground Bounce, you're ready for the intermediate video course, Twists, Flips, and Beyond (Part 1), where you'll start learning the really cool tricks. 

Keep practicing,

"Slinky Josh" Jacobs

Founder, HyperSpring Toys


PS: If you'd like to read more about the physics of the spring constant, check out this WikiHow article and the Wikipedia page on Hooke's Law.