# Trampoline double jumping

1. Jan 6, 2008

### h.g.Whiz

suppose you had a trampoline that you could increase the tension in between jumps so that every time you landed. (and there is plenty of room between the surface and the ground) what would happen .what if someone double jumps then two people etc.. would your jump height keep increasing

2. Jan 7, 2008

### keinve

it would increase to some extent, till the tension would be similar to jumping on a flat surface. it would most likely break at that point, assuming you made a big enough tension increase in one jump, otherwise, it would gradually decrease... that's not clear, is it?

3. Jan 7, 2008

### stewartcs

You would eventually break a leg or something. Your body couldn't handle the extra stiffness of the springs. It would be like jumping off of a tall building and bouncing as you hit the ground.

4. Jan 7, 2008

### rcgldr

Increasing the tension won't increase height, it just increase the g forces involved during the bounce. I'm not sure what you mean about two people, but one or more persons can provide the energy to bounce another person on a trampoline.

5. Jan 7, 2008

### Math Jeans

Exactly, you would decellerate, and accellerate quicker for each bounce, however, we all know what happens when you decellerate too quick.

6. Jan 7, 2008

### dst

The only way your jump height would increase is if you pumped energy into the system somehow. Increasing the tension doesn't change a thing about that.

7. Jan 8, 2008

### nanoWatt

If the trampoline resonated with you, meaning, just as you went up, it stiffened to give you more acceleration up, I believe then you would have a partial harmonic-oscillator. partial because it's not a continuous spatial displacement.

If then you loosened it as you fell to allow for more displacement, and tightened it again in the periodic fashion, you definately could increase your height.

8. Jan 8, 2008

### Math Jeans

However, tightening it only does one thing: it increases the rate at which you decelerate and accelerate on the trampoline with the same displacement of the trampoline on landing.

A better way to achieve the same result without hurting yourself (provided that the springs are perfect, and you recieve the same force upward that you do downward), is to dig a hole under the trampoline. Instead of increased acceleration through the tightened springs, the higher you bounce, the more displacement will occur in the springs, and you will get higher without hurting yourself. However, in reality, this will not work.

9. Jan 8, 2008

### nanoWatt

That would be correct assuming a rigid body. With biological systems, it's more complicated. IRL, the tighter membrane might make you react to avoid injuring yourself.

To get good height, start with more potential energy like jumping from above the trampoline onto it. Don't go crazy though. I've heard stories of kids who tried jumping from a tree onto a trampoline. Not good.

10. Jan 8, 2008

### dst

And where does the energy to tighten & loosen it come from?

11. Jan 8, 2008

### Math Jeans

Perhaps it could be possible to create a contraption that puts a plate at each end of the spring in which one plate is at a distance from the end that extends. When the spring then extends to a certain point, it would make contact with the plate and complete the circuit, in which the plates would then apply force to the ends of the springs causing more force upward from the trampoline before returning to their original position.

It would take a little work, but it doesn't seem like a hard thing to do.

12. Jan 8, 2008

### dst

I meant as a restricted version of the original problem, i.e. nothing but gravity supplies the original energy.

Rephrased: Is there a maximum jump height, if we have nothing but gravity, the trampoline, human and well, a surface for the trampoline to rest on?

13. Jan 8, 2008

### Math Jeans

Well, there is a maximum hight considering we are taking into account wind resistance. Eventually as we all know, you will reach terminal velocity (if it is a perfect trampoline). When your speed does reach terminal velocity, the difference in hight will depend on at which point in the trampoline's acceleration do you reach terminal velocity, and over time, that will be a constant point, and thus a maximum hight.

14. Jan 9, 2008

### rcgldr

A few web sites mention olympic competitors reach heights of 25 to 30 feet (top of head to the ground), which translates into an actual bounce height of 15 to 20 feet, with a trampoline that is 3.75 feet (45 inches) above the gym floor.

A competition trampoline "bed" is web made up of paired 1/8 inch diameter nylon chord, spaced about 5/8 inches apart, (called an "ozzie" bed, since an Australian manufacturer apparently made the first ones of this type), and is 7 feet wide by 14 feet long. There is very little air resistance on this type of trampoline bed, so the bounces are very elastic, not requiring a lot of energy. Former USA competition trampolines used 1/4 inch wide canvas strips instead of the nylon chords, and also had very little air resistance.

Home type trampolines typically have significant air resistance, and are not as energy efficient. Really old ones used canvas strips about 3/4 inch wide with about 1/4 inch wide holes. Outdoor trampolines use some type of black mesh which also has significant air resistance.

Last edited by a moderator: Sep 25, 2014
15. Jan 9, 2008

### nanoWatt

Man that's crazy. I've been up on a utility pole at 30' above the ground, and that's scary. Though, I've also been at 60-feet as well which has a very nice view.

16. Jan 9, 2008

### dst

Right that's just monstrous. I guess the added energy comes from the trampoliner pushing their own weight, so to speak, adding to momentum and that gets stored + released by the trampoline. So it should be, in theory, possible to jump higher and higher and higher if you upped the tension each time (obviously G-forces would limit things somewhat).

30ft is just scary.