# The Naked Scientists Forum

### Author Topic: does bouncing on a space hopper whilst on a trampoline get me higher?  (Read 3874 times)

#### paul.fr

• Guest
##### does bouncing on a space hopper whilst on a trampoline get me higher?
« on: 22/05/2007 01:01:31 »
Do you remember space hoppers from years back? Well i could bounce about a meter or so on one of them, on a trampoline i can bounce a few meters. If i bounced on my space hopper whilst on a trampoline, how high could i get?

#### another_someone

• Guest
##### does bouncing on a space hopper whilst on a trampoline get me higher?
« Reply #1 on: 22/05/2007 02:38:50 »
I suspect you would fall over (try balancing on a space hopper as you hit the trampoline - not an easy thing to do I suspect - not that I have tried).

First problem will be one of resonance.  The way that both space hoppers and trampolines work is by excited resonance (a specific mass - namely your body mass - and a specific spring vale, will create a resonant system).  If the space hopper and the trampoline are tuned to different resonant frequencies, you will probably lose energy.  If they were tuned to identical frequencies, then I can imagine you could create a stronger resonant system (if maybe difficult to manage).

#### lyner

• Guest
##### does bouncing on a space hopper whilst on a trampoline get me higher?
« Reply #2 on: 22/05/2007 11:42:54 »
another_someone is right about the resonance thing, of course and the two resonant frequencies would need to be equal - or at least, harmonically related.
As usual, I will bring energy into my argument.
Each time you bounce, you put some energy into the system with your leg muscles. The height you reach depends on the kinetic energy with which you start each upward trip.
(Potential Energy Gained = kinetic energy lost)
When you return, you have alomst the same KE as when you left (less the friction losses) The springs and fabric stretch and store most of your KE plus the energy from your legs, returning it on the way up. The limit to your height reached will be when your legs just supply enough energy to make up for what you lost due to friction each bounce.
Your space hopper would probably introduce MORE loss into the system so you would probably not get as high, in fact.
You could discuss this with the doctor in casualty, when you get there!
A more efficient system would get you much higher - suspending yourself on a long spring and carrying some heavy masses  would work well, once you had found the right (resonant) frequency.
One of the problems in any such system is 'matching' the energy input to the system. There will be an optimum length of leg and body mass for getting the best height on a particular trampoline. A mouse, for instance, wouldn't get anywhere on a human trampoline but could jump quite high (with practice) on a specially designed one. Though, whether he would be bothered to, is another matter.
Btw, your achilles tendon (and a kangaroo's even more so) stores a significant amount of energy whist you are running. You spring higher than you would with a non resilient  tendon.

#### paul.fr

• Guest
##### does bouncing on a space hopper whilst on a trampoline get me higher?
« Reply #3 on: 22/05/2007 13:49:00 »
another_someone is right about the resonance thing, of course and the two resonant frequencies would need to be equal - or at least, harmonically related.
As usual, I will bring energy into my argument.
Each time you bounce, you put some energy into the system with your leg muscles. The height you reach depends on the kinetic energy with which you start each upward trip.
(Potential Energy Gained = kinetic energy lost)
When you return, you have alomst the same KE as when you left (less the friction losses) The springs and fabric stretch and store most of your KE plus the energy from your legs, returning it on the way up. The limit to your height reached will be when your legs just supply enough energy to make up for what you lost due to friction each bounce.
Your space hopper would probably introduce MORE loss into the system so you would probably not get as high, in fact.
You could discuss this with the doctor in casualty, when you get there!
A more efficient system would get you much higher - suspending yourself on a long spring and carrying some heavy masses  would work well, once you had found the right (resonant) frequency.
One of the problems in any such system is 'matching' the energy input to the system. There will be an optimum length of leg and body mass for getting the best height on a particular trampoline. A mouse, for instance, wouldn't get anywhere on a human trampoline but could jump quite high (with practice) on a specially designed one. Though, whether he would be bothered to, is another matter.
Btw, your achilles tendon (and a kangaroo's even more so) stores a significant amount of energy whist you are running. You spring higher than you would with a non resilient  tendon.

I thought someone would bring energy in to the problem .So, how about those balls made of rubber bands that kids, and bored adults make. Do they gain or lose energy when bounced?

#### another_someone

• Guest
##### does bouncing on a space hopper whilst on a trampoline get me higher?
« Reply #4 on: 22/05/2007 14:13:10 »
I thought someone would bring energy in to the problem .So, how about those balls made of rubber bands that kids, and bored adults make. Do they gain or lose energy when bounced?

They cannot gain energy as such, but if they can retain enough energy from one bounce to the next, and then you (the human cargo) adds a bit more energy in each bounce, then there will be a cumulative build up of energy.  It is exactly analogous to a swing that you sit on, that is also a resonant system which has a relatively low loss at its resonant frequency, so if you give it a slight kick at the right point in each cycle (and thus synchronous with the resonant frequency) you can build up ever more energy in the system.

#### The Naked Scientists Forum

##### does bouncing on a space hopper whilst on a trampoline get me higher?
« Reply #4 on: 22/05/2007 14:13:10 »