yeah thats exactly what i was saying...

Plane would need to go 200mph ground speed with a tail wind of 100mph. If it were to take off..

(remember the theoretical planes take off speed on a windless day was 100mph air speed)

haha, good one :)

Yes yes, your about 5 pages too late.. Read the whole thread before replying :P

Go stick your wang in that propellor you cheeky sod - if you had the mentality you'd see I was consistently correct. http://www.discussworldissues.com/fo...es/tongue1.gif

For the love of Gordon was just an expression lol, but feel free to think I meant you [rofl]

I don't know if it's been pointed out, but this sounds wrong.

2 cars head on at 60mph is a combined speed of 120mph. A bit like 1 car going 120mph and hitting a stationary car.

It must be possible to understand the plane thing. Forward motion comes from the jet engine/props. The wheels are only there to keep its belly off the ground.

Here's another question. If the treadmill only spins to match the force from the wheels.... would the treadmill need to spin at all if the plane was being powered forward by a jet. Would the wheels just roll over the top without exerting force on the treadmill?

No, 2 cars hitting each other at 60mph is the same as one car hitting a solid wall at 60mph.

you have 120mph of force/engergy or what ever you call it, and it is divided into 2 cars. So each car gets 60mph of damage.

So it should be the same as hitting a solid wall at 60 also.

Yeah and the plane on treadmill is so blatantly obvious to me now i dont know why i needed to ask in the first place.

Think of the plane being pulled off the belt by a winch, the winch does not need to pull the plane faster or with any more force regardless of is its on a conveyer belt or the ground. The plane pulls its self through the air and thus has nothing to do with the ground.

Plane is driven forward by the air it displaces - so only effected by wind speed, not ground speed
A car is driven forward by its wheels - so is effected by ground speed
A rocket is driven upwards by pure thrust - so is only effected by gravity and air resistance

I know [rolleyes], that's why i didn't take it seriously - esp' as you were getting at one of the other chaps.
BTW, how's the watch working out?

Forgot, the horse would lose because it'd be dead http://www.discussworldissues.com/fo...ilies/sad1.gif

No. Two cars, each travelling at 30mph towards each other, colliding is theoretically the same as one car travelling at 60mph hitting a stationary object.

No its not.

Its like one car going 30mph hitting a stationary object.

LOL - you're winding him up right?

I'm still lolling at this. OK....think about this.

Kinetic energy is generated by any object that is moving. When that object suddenly stops that energy has to be dissipated. If two moving objects collide then both sets of kinetic energy have to be dissipated. If a moving object collides with a stationary object both can share the dissipation of the kinetic energy.

http://en.wikipedia.org/wiki/Collision

You're not too sharp on this relative motion point are you? It's the crux of everythng you are trying to understand in this thread.

This was also debunked on Mythbusters.

They originally claimed the same as you. Loads of viewers wrote in and complained saying they were wrong.

They tested it - they were wrong.

2 cars at 30 mph hitting each other head on is the same as one car hitting a wall at 30mph.

EDIT: Here is a decent explanation:

http://warp.povusers.org/grrr/collisionmath.html

No?

look. 2 cars head on at 60mph =120mph of force. divide that force between the 2 cars and you have 60mph of force being afflicted to each car. Both cars are smashed up the same as if they would have hit a solid unbreakable wall at 60mph.

because the solid wall does not absorb any of the force, so the car gets the full 60mph of damage.

Its so obvious its easyer to understand than the plane thing.

2 cars at 60 = 120 they hit each other, the force is divided by 2. Each car get same damage as 60mph if hitting a solid wall.


thanks for insulting me Quantumdefect, when actually its blatantly obvious you are wrong. :D

See my previous post. You and Quantum are dead wrong on this subject i'm afraid.

yea

You cant magically get both cars getting a force of a 240mph if they are both going 60mph. 2 x 60 = 120 not 240.

120 / 2 = 60....

No. Two cars, each travelling at 30mph towards each other, colliding is theoretically the same as one car travelling at 60mph hitting a stationary object. Yes, the physics makes it clear that the impact velocity of two head-on objects will be viewed from the perspective of any one of the objects as being a collision equating to double the object's velocity. It's basic relativity, after all. However, impacts are about forces. In the case of each object in the collision, their change in momentum is not a change in relative momentum but an absolute one. So a 1000 kg car doing 20 m/s will have a momentum of 20,000 kgm/s and so if the impact time is 2 seconds, for example, that equates to an impact force of 10 kN and not 20 kN.

They wont understand that if they cant understand it put simply like, 2 cars going 60 is equal to 120
Divide 120 between the 2 cars, and you get 60.

So a car going 60 and hitting a solid unbreakable wall = 60mph divided by 1.

2x60/2=60
1x60/1=60

I hadn't thought about the impulse; I stand corrected.

StonedOne, you aren't understanding it either, just getting the correct result through incorrect reasoning.

Except it just isn't like that - your maths 'works' but there's no reasoning behind it, other than the numbers fit the problem.

Part of the misunderstanding from people comes from one of two areas: (1) you get taught about relative velocities a lot in maths and physics, and far too many teachers then carry this on through to collisions. I've even seen it been done incorrectly on A-level exam papers so it's not surprising that a lot of physics students think about the collision stuff incorrectly (when I was an A-level student myself, I always got the 'wrong' answer in such problems and couldn't understand where I was going 'wrong'!).

(2) Government and road safety campaigns have always maintained that head-on collisions are the worst accident to have. While this may be true, it's not, of course, due to the collision velocity being doubled but it's about the surrounding environment, e.g. other vehicles colliding with the impact vehicles and so on.