You thought you had enough of it at school (Physics...)

[bayrodney]

Ok, this question was raised while we were moving some furniture to our new house (more like a shed at the moment). We were moving a trampoline on a trailer (Love the Tramp) and i brought up the question: What if i was to jump on the Trampoline while it was travelling 80kmph (About 50mph) down the road, would i fly backward, or land back on to the trampoline?
Bring it on Nerds, this is your time to shine.
Thanks

 

[Fizl]

Land back on the trampoline I think. I don\'t understand the details - but it is to do with the theory of relativity I believe

Shaz

 

[bayrodney]

wow, they swarm in quickly, lol, joking...

I was thinking that to...
but..
we will leave it to the professionals

 

[Infidel Castro]

The only problem is air/wind resistance. As long as you\'re travelling at the same speed you\'d land back on the trampoline. Same as on a bus, you don\'t land further back if you jump on one of those as you\'re body mass is travelling at the same speed. With the trampoline, the wind resistance the front of your body causes would be a nightmare compared to a car or vehicle, and your time in the air would see you fall back a bit. Don\'t know how far though. Why don\'t you try? lol

In a vacuum it would be brilliant to see the laws upheld, but again, you\'d suffocate. Want to try it? lol

 

[bayrodney]

ok, so i can bounce as high as i want on this trampoline, and will land back on it....
but it depends on the air resistence...?

 

[Tony Manero]

Originally posted by bayrodney
Ok, this question was raised while we were moving some furniture to our new house (more like a shed at the moment). We were moving a trampoline on a trailer (Love the Tramp) and i brought up the question: What if i was to jump on the Trampoline while it was travelling 80kmph (About 50mph) down the road, would i fly backward, or land back on to the trampoline?
Bring it on Nerds, this is your time to shine.
Thanks

your head explodes.


just that

 

[bayrodney]

Really...!
I am gullible by the way...

 

[Infidel Castro]

Originally posted by bayrodney
ok, so i can bounce as high as i want on this trampoline, and will land back on it....
but it depends on the air resistence...?

Aye, but only in a vacuum my good man.

 

[Tony Manero]

thats why your head explode. u haven\'t seen any SF movie? lol

 

[Modderrhu]

From one of Newton\'s laws, an object will keep on moving in a straight line unless it is acted on by another force. Two forces will act on you after you have jumped, wind resistance which will tend to decelerate you, and gravity which will pull you back to the trampoline. So, you\'d land back on the trampoline, a little behind where you started off from.

Easy, huh?

 

[Tony Manero]

Originally posted by Modderrhu
From one of Newton\'s laws, an object will keep on moving in a straight line unless it is acted on by another force. Two forces will act on you after you have jumped, wind resistance which will tend to decelerate you, and gravity which will pull you back to the trampoline. So, you\'d land back on the trampoline, a little behind where you started off from.

Easy, huh?

THEN your head blows off lol

 

[Mosch]

Orginal gepostet von Modderrhu
From one of Newton\'s laws, an object will keep on moving in a straight line unless it is acted on by another force. Two forces will act on you after you have jumped, wind resistance which will tend to decelerate you, and gravity which will pull you back to the trampoline. So, you\'d land back on the trampoline, a little behind where you started off from.

Easy, huh?

Wait, the trampoline has a gravitational pull? Orbit too, eh?

Na, seriously, I don\'t know a lot about physics, but I am pretty sure that when you jump upwards, you accelerate upwards. While the trampoline accelerates forward. AKA away from you. Then it will seem as if the ground accelerates towards you. Actually, that\'s just you thinking what a stupid idea that was.

Seriously, think about it. How could you jump out of something that\'s moving (which works. believe me on that one ) if you automatically moved with the object? Also, you will not fly backwards, by the way: The car would just move away.

 

[Grey Area]

I can\'t tell if the \"theory of relativity\" comment was serious or not. Whatever the case, this problem certainly has nothing at all to do with either of Einstein\'s theories of relativity.

Originally posted by Mosch

Wait, the trampoline has a gravitational pull? Orbit too, eh?

Na, seriously, I don\'t know a lot about physics, but I am pretty sure that when you jump upwards, you accelerate upwards. While the trampoline accelerates forward. AKA away from you. Then it will seem as if the ground accelerates towards you. Actually, that\'s just you thinking what a stupid idea that was.

Seriously, think about it. How could you jump out of something that\'s moving (which works. believe me on that one ) if you automatically moved with the object? Also, you will not fly backwards, by the way: The car would just move away.

The gravitational effect of the trampoline is totally insignificant in this problem.

The word \"accelerate\" is used incorrectly in your post. After you leave the trampoline, the only forces acting upon you are your weight and air resistance. Your weight acts to accelerate you towards the earth, and the air resistance reduces your forward velocity. The trampoline, on the other hand, continues to travel at the same speed, and doesn\'t accelerate at all.

As has already been mentioned, the only reason for you not to land back on the trampoline is air resistance slowing down your forward motion.

 

[Modderrhu]

Originally posted by Mosch
Wait, the trampoline has a gravitational pull? Orbit too, eh?

Yeah, yeah, yeah, but they\'re negligible. Nitpicker!

Originally posted by Mosch
... when you jump upwards, you accelerate upwards. While the trampoline accelerates forward. AKA away from you.

The trick is to think about the problem on two axes. The vertical (jump and gravity) and horizontal (vehicle and initial velocity)

When you jump, the trampoline and your legs are exerting a force to accelerate you upwards. As soon as you leave the trampoline, that force stops, and gravity starts to decelerate you again. Acceleration is the change in velocity. Just as velocity is a measure of how quickly distance changes. So on the vertical axis, you jump up and gravity pulls you down again. Actually, the presence of the trampoline has no effect other than to extend your flight time, allowing air friction a longer period to exert its force on you.

But the car is moving forwards... initially you are moving with the car. You jump. What force is there to change that forward movement except for air resistance? So, with only air resistance working to decelerate your horizontal velocity, the chances are that you\'ll pretty much keep pace with the car and land back on the trampoline, albeit a bit further back.

My head has just blown off.

 

[frenchkid]

hey highschool physiques !!
You know I get every morning thinking I don\'t have to do that kinda stuff anymore

As for the answer, like some said (asuming we\'re using a standard earth referential)
If you\'re moving at the same speed as the trampoling will jumping on the trampoling ( in the same care for exemple) you should land back on it if the the air resistance dosn\'t slow you down enougth and if you jumped straigth up. the two options seem unlickly too me so, if you should try it, I\'ll bet that you\'ll fall somwhere els then on the trampoling.

Now if kendaric is around here I\'m sure he can put all that in equation I just remember it as somthing to do with integrating the acceleration acceleration. Oh and if you want to nitpick you would have to consider archimede ( normally it\'s not taken in account in the air).

 

[Mosch]

First of all, I have no idea about physics, save for the electricity part - so give me a little leeway when I use the wrong phrases, please

Secondly, I seem to have misunderstood the idea. So you are saying you are driving 80 km/h, then doing the jump on the car, instead of doing the jump onto the moving car? In that case I humbly bow my head and agree to the theory.

Thirdly: How can that help me to improve my NMM?

 

[Tony Manero]

i still don\'t understand when ur head blows off ???

 

[LordofthePit]

Actually you don\'t need a vacuum to do it.. the only problem is -like mentioned before- the air resistance. So you could do it in a bus or even better, a train.. now I suppose that most public transportation doesn\'t allow you to take a trampoline with you, but you can just go stand in a bus and jump as high as you can, you\'ll see that you end up on the exact(provided you jump straight up) same spot you jumped.

Why is this? Because when you are in the bus (in a car/on a trailer) you move with it at the same speed and there is nothing that slows you down except for air resistance if you are outside. It was in fact Newton who discovered it and it is one of the three of his famous laws of motion (so not relativity then ):

Every object in a state of uniform motion tends to remain in that state of motion unless an external force is applied to it

Now this only works if the vehicle is travelling at a constant speed.. once it accelerates or brakes you will move backwards or forwards in relation to the vehicle (that\'s why you\'ll feel being pushed into your seat when it accelerates and nothing if it travels at a constant speed). Hope this clears it up somewhat..
Oh yeah apart from all this, your head WILL explode lol

 

[Fizl]

I knew a famous scientist did it, and I saw it on Brainiac (illustrated with a rickshaw rider and a dropped egg above his head)

Newton..Einstein...who knows the difference lol

Shaz

 

[Kendaric]

Well, there are quite a few parameters to take into account there...
Basically, when moving in the air you\'re subject to air resistance, it\'s value being proportionnal to v*v (v= your speed), but also your shape, the density of the air. Raw formula :

Fx = 1/2*t*S*Cx*v²

t = density of air, 1,224 kg.m^(-3) at our altitude
S = frontal maximal surface (I\'d say we can reasonably approx. it by your width*height. Anyway as we maximate it it\'ll no be a danger for further calculs)
Cx = the hard part. First hard to translate. \"Coefficient de trainée\" in French. Do whatever you will with that...
I\'d say we can approximate you into a cylinder . Numerically, Cx would be close to 0,7 in that case. And that\'s HUGE.
v = speed, 80 km/h there, that\'s to say 22.2 m/s

All right, we\'ll say there is no other wind at the moment you jump. Then the problem will be equivalent to you jumping on a stationary trampoline with wind blowing at 80 km/h. Frontally it\'ll be worse for you (worse \"coefficient de trainée), so let\'s see what it does then.
If you\'re 1,80 meter high, 45 centimeters wide without the arms.

Then: Cx = 1/2 *1,224 * 1,8 * 0,45 *0.70*22,2 * 22,2
Cx = 171 N

It\'s huge. Well, for further calculs you\'d get a non-linear differential equation of the first order with which you can calculate 1/v (do you want it frenchkid? ), you then integrate to see how far behind you end up. The heavier you are the closer you\'ll land back to your starting point. I\'m not so sure everything up there is accurate, I\'ve got no notions of aerodynamics, and it was done a bit too fast... If I\'m wrong please tell me where the error is.

Enough physics for now... They tell you: \"Don\'t do it!!\". Even if you control what you\'re doing a single wind gust could make you fall outside your trampoline. And at these speeds it\'s deadly. Besides you\'ll be standing which means you\'ll land badly.

It\'d be saner at 20 km/h maximum. Even then I\'d strongly advise against it. Cars coming from the other side, you don\'t control the wind: too many random factors that mean you\'ll be playing with your life . Even if you do land back on the trampoline.