Please Can Someone Help!

[benny3008]

Right, this has been driving me mad all day and if anyone can come up with a scientific answer (in simple terms) I would be very happy.

Imagine you have an articulated lorry, a bus, whatever, just an enclosed moving vehicle, you're inside it and the vehicle is moving...you throw a ball in the air, does it...

A. Fall straight back down into your hands or...
B. Stay put and land on the floor further back in the vehicle.

Asked my mum this earlier and she said well of course it would land back in your hands, so instead of a ball, I changed it for a remote control helicopter, or similar, hovering in the air at a set point, vehicle moves forwards, what happens to the helicopter, stay in position within the vehicle or stay in position with relation to the outside world?

What do you think, or do you know the answer?

[david small]

Stay in position within its constant environment. I.e. The vehicle. Same as on a train, plane, etc.

[maggiebee]

Not too sure, but have often had grandchildren in the back seat of my car and when they throw a ball etc up it just lands back in their hands.

[benny3008]

What if, say it was inside an articulated lorry and the rear doors are open, same story, regardless of where in the trailer you are stood? Close to opening or close to front.

[EDDIE51]

^^ Yes Same story.

[Buenchico]

Newton's First Law of Motion states "Every object in a state of uniform motion tends to remain in that state of motion unless an external force is applied to it".

The ball is already moving forwards (with you and the truck) before you throw it. So, in accordance with Newton's First Law, it will continue to do so unless something stops it (which it doesn't).

The upward force applied to the ball, as you throw it, acts as a vector at right-angles to the forward motion (and can thus have no effect whatsoever upon that forward motion).

Hence the ball will fall back into your hands.

Well that's the way that physics worked when I used to teach the subject but, with all these changes to the curriculum, who knows these days?
;-)

[benny3008]

So, use the remote control helicopter for example, same outcome? Surely there has to be a point within an open lorry trailer at which the helicopter will become outside instead of inside, what's the difference between doors being open or closed, surely you'd have the same outcome would you not?

[EDDIE51]

^^ I was going to put something along those lines Chris but I thought that someone who has to ask such an obvious question would struggle to comprehend Newton's first law and the concept of vectors.

[benny3008]

Obvious question?! Surely such an obvious question would not have such an explanation as above.

[retrocop]

//maggiebee
Not too sure, but have often had grandchildren in the back seat of my car and when they throw a ball etc up it just lands back in their hands.//

When my grand daughters ae safely strapped in their car/booster seats in the back and throw something heavy in the air it usually lands in Grandad's nether regions whilst trying to concentrate on his driving !!!
They are too young to understand physics so perhaps I will suffer less as they mature. !! :-)

[EDDIE51]

If you flew a remote control helicopter out from the back of a moving truck ,as soon as it was outside it would be affected by the air flowing past it, which would blow it away. Thus maintaining Newton's first law as the air flow would be an outside force ( 'something that stops it' in Buenchico's post)

[benny3008]

And if the helicopter were just hovering at a set point within the trailer, would it leave the trailer as the lorry moved or stay put within the trailer.

[EDDIE51]

No it would not move,it would stay at the same point in the trailer. Newton's first law again !

[Gizmonster]

It would all depend on its environment.
If the back door of the trailer is open, but the air remains still, then no external force is acting on the helicopter, so it would travel forward with the trailer.
If the air was "wooshing" around, then this would be an external force and would affect the movement of the helicopter accordingly.

[Old_Geezer]

A. The frame of reference for both you and the ball and everything else in the vehicle is the same so you move together. Inside the ball simply goes up and down.

(Viewed from outside you and the ball also move horizontally together, your motion describes a straight line, the ball's a curve.)

[Old_Geezer]

The helicopter is a more interesting question. You can send you helicopter out of the back door if you wish but that would be under its own power. Once out it would find conditions somewhat different. It is no longer in a the still air of the moving vehicle. It's air draft is down towards an unmoving road rather than the moving vehicle. Things change. It'd be interesting to see how the actual forces change and how. I leave that up to the physics teacher.

[Tilly2]

You'd catch it....hopefully.

[ToraToraTora]

Ok this is a standard thought experiment, we must ignore the air to illustrate the principle. say there is a cannon facing vertically up on an open back truck going at 100MPH. The cannon is fired, were does the ball land? The answer is back in the cannon. You see to the truck the ball goes up and down but to a stationary observer the ball scribes an arc from the cannon to the cannon. Same principle with you, helicopter, ball, kitchen sink everything.

[Clanad]

But... but... one cannot disregard the air in Triple T's example, because the changes wrought on the path of the cannon ball will be affected by the "open back truck"... The ball cannot descend back into the cannon's muzzle since, as pointed out earlier, the moving ball (it doesn't matter how fast the truck is going BTW)is being affected by the "external force" of the air.

All things considered, once the air movement is discounted/non-existant our pal Newton has it nailed...

[whiskeryron]

Is it the same sort of principle as the old tale of the truck driver who keeps stopping & banging the side of his truck, when asked by a following motorist why he was doing it he replied well this is a 2 ton truck & I am carrying 3 tons of Budgies & if ever they all settle at the same time they will surely break the truck springs ?

[ToraToraTora]

clanad I'm disregarding the air merely to illustrate the relativity, it is clear than in reality the cannon ball would miss the muzzle but it would be close and it would prescribe an arc to the stationary observer. It's like the falling object experiment with the heavy and light balls done by Galileo, he knew that objects will fall at the same rate if the air is removed but to demonstrate he had to use balls that were different weights but similar air resistance. An experiment later done with a feather and a hammer by David Scott on the moon.