Is this scientific idea really feasible?

[TheK1ll577]

My friend says this would work and although i am not a huge science dude i have no doubt that this would not work, can some1 explain the technical stuff i don't know?

 

[Danger]

Welcome to PF, TheK.
Very simply, the device is pulling against itself. The only possible movement from this arrangement is that the magnet could pull the boom in toward the front of the truck. (And that, by the way, would take a very powerful magnet.)

 

[jVincent]

If you make the same drawing, but replace the magnet and the metal plate with a rubber band stretched between the two points, you have physically the same situation.

You could argue using Newtons third law, which states that every action has an opposite reaction of the same magnitude.
The metal plate will be pulled forwards, but the magnet will be pulled backwards with the same magnitude, and since both objects are attached to the truck, the net force on the truck is zero. However if the force is large enough, the arm holding the magnet would likely deform or break.

 

[Pengwuino]

Imagine if instead of a truck, it were you... made out of metal. If you got that magnet and put your arm out and pointed it towards yourself, your body would feel attracted to the magnet, but the magnet would also feel attracted towards your body. Thus, both would move towards each other and eventually attach.

I know there's a VERY clear analogy to this that would make it very obvious why this won't work but I can't think of it at the moment.

 

[vlado_skopsko]

You know the story of Baron Munchausen, lift himself up by his ponytail from the quicksand. Does not work :)

 

[cragar]

However if you had an electromagnet and turned it on attracting the iron and then turned off the magnet when the iron was flying at the magnet, after the iron hits the magnet and bounces back, it will move forward a little. Because the change in momentum is greater when it hits an bounces back, then when the iron originally pushed off the truck .

 

[espen180]

That would not work either. At any point in time when the metal piece has a certain (horizontal) momentum, the truck will have exactly the same, but opposite, horizontal momentum.

 

[Office_Shredder]

However if you had an electromagnet and turned it on attracting the iron and then turned off the magnet when the iron was flying at the magnet, after the iron hits the magnet and bounces back, it will move forward a little. Because the change in momentum is greater when it hits an bounces back, then when the iron originally pushed off the truck .

You still have the problem where the electromagnet was pulled towards the iron as well. So maybe you ended up moving forward a little bit, but it's at the expense of your electromagnet being directly next to your iron plate. Either you need to reposition it or you've stopped moving.

I would also be surprised if the huge power expenditure required to drag a truck like that is anywhere close to efficient (keep in mind that electromagnets are powered by electricity)

 

[cragar]

That would not work either. At any point in time when the metal piece has a certain (horizontal) momentum, the truck will have exactly the same, but opposite, horizontal momentum.

Yes it would , it would be like standing in a railroad car and throwing baseballs at the front of the car. When you throw the baseball you might move back a little but when it hits the front of the car and bounces off the impulse you deliver is greater and it will move forward a little bit. It's not very efficient I'm just saying it will happen .

 

[Jon Richfield]

Yes it would , it would be like standing in a railroad car and throwing baseballs at the front of the car. When you throw the baseball you might move back a little but when it hits the front of the car and bounces off the impulse you deliver is greater and it will move forward a little bit. It's not very efficient I'm just saying it will happen .

Are you trolling us?
That is elementary. It would only work to the extent that you could make use of the friction against the ground etc. A clearer example would be that you could stand on a rug and move across a floor by jumping and kicking it sideways repeatedly. Without friction and similar influences you would get nowhere (apart from the option of throwing the rug in the opposite direction and not catching it)

Personally I reckon the clearest illustration would be along the lines of the Munchausen example. Replace the magnet with a rope and turn the whole kaboodle on its side so that it is like lifting yourself by your proverbial bootstraps. That has the advantage that K could try it for himself and see why it doesn't work. Having convinced himself, he could invite his friend to demonstrate the contrary either horizontally or vertically. :tongue2:

 

[Bob S]

My friend says this would work and although i am not a huge science dude i have no doubt that this would not work, can some1 explain the technical stuff i don't know?

If I were sitting on a donkey, and if I held a carrot on a stick in front of the donkey, the donkey moves forward. Isn't this the same?

 

[Danger]

If I were sitting on a donkey, and if I held a carrot on a stick in front of the donkey, the donkey moves forward. Isn't this the same?

No. That would be the same as driving the truck with its wheels.

 

[I_am_learning]

Ask your friend to lift himself up. He can't. (Although he can lift someone heavier than himself)

[But if he jumps up, and asks -"how is it possible then" then don't ask me! The question of why people are able to jump has always troubled me! )

 

[georgir]

In the magnet situation, the magnet is pulling the truck, but also the truck is pulling the magnet back equally, and as a result their center of masses stays immobile.
In the donkey situation, the carrot is pulling the donkey but the donkey is not pulling the carrot back, so you end up with a net impulse gain ;)

 

[Danger]

the carrot is pulling the donkey but the donkey is not pulling the carrot back, so you end up with a net impulse gain ;)

Not quite. The donkey is walking toward the carrot because it's too stupid to realize that it can't be reached.

 

[DaveC426913]

TheK1ll577, consider this:

If I hold a magnet near a large metal object, and let it go, it will jump to the metal object, right? I'm just establishing that, when it comes to the attraction between a magnet and a metal object, it works both ways, right? This isn't Wile E. Coyote here, a magnet will not remain stationary as it pulls a rocketship toward it. Magnets move. Agreed?

Now, look at the diagram. You have a magnet attracted to a large metal plate. Why would we assume that it would be the truck that would try to move toward the magnet? It is just as valid to assume that the magnet should move toward the truck.

In fact, if your friend were right, one might expect the truck to actually move backwards, pushed by the magnet, which is pulling towards the plate.

This is every bit as valid as the original scenario (where the truck is pulled forward). Take a moment to convince yourself of this.

Now you have two situations which are identical yet exactly opposite each other. They can't both be true!
And if they're not both true, yet one can't be true without the other also being true (since they're identical) - the only option left is that they're both false.


(Or, simply put, the magnet pulls on the truck, tugging it forward; the truck pulls on the magnet, tugging it backward. Assuming the arm is rigid, they cancel out. The truck/magnet does not move.)

 

[cragar]

Are you trolling us?

you are good!

 

[TheK1ll577]

TheK1ll577, consider this:

If I hold a magnet near a large metal object, and let it go, it will jump to the metal object, right? I'm just establishing that, when it comes to the attraction between a magnet and a metal object, it works both ways, right? This isn't Wile E. Coyote here, a magnet will not remain stationary as it pulls a rocketship toward it. Magnets move. Agreed?

Now, look at the diagram. You have a magnet attracted to a large metal plate. Why would we assume that it would be the truck that would try to move toward the magnet? It is just as valid to assume that the magnet should move toward the truck.

In fact, if your friend were right, one might expect the truck to actually move backwards, pushed by the magnet, which is pulling towards the plate.

This is every bit as valid as the original scenario (where the truck is pulled forward). Take a moment to convince yourself of this.

Now you have two situations which are identical yet exactly opposite each other. They can't both be true!
And if they're not both true, yet one can't be true without the other also being true (since they're identical) - the only option left is that they're both false.


(Or, simply put, the magnet pulls on the truck, tugging it forward; the truck pulls on the magnet, tugging it backward. Assuming the arm is rigid, they cancel out. The truck/magnet does not move.)

You totally won me 50 bucks dude, thank you everyone.

 

[DaveC426913]

You totally won me 50 bucks dude, thank you everyone.

Cool. Have a ball spending what's left of it after you get my consulting bill.

 

[Danger]

Cool. Have a ball spending what's left of it after you get my consulting bill.

Your bill? Who was the first respondent to this question? :grumpy:

 

[Born2bwire]

Your bill? Who was the first respondent to this question? :grumpy:

I can't argue with Dave. No matter the content of his post, the disappointing glare of his avatar saps all the joy and life out of me. Forgive my trespasses oh Dave!

 

[Danger]

the disappointing glare of his avatar saps all the joy and life out of me

Yeah... easy for you to say. Try living in the same country with him for a few years and see how funny it seems.

 

[Ranger Mike]

nuff said

 

[Relay]

I love perpetual motion machines. Too bad none work.

 

[Jon Richfield]

I love perpetual motion machines. Too bad none work.

Well, surely that depends on how picky you want to be? If you would be satisfied with a perpetual motion machine of the second kind, and would accept a few times the age of the universe as perpetuity, then a nice big rocky planet circling a remotely intergalactic white dwarf at say an orbital radius of one light year seems pretty perpetual to me. In fact, if you were not too greedy, you could elaborate on the system slightly and milk it of enough energy to run your PC for longer than a political speech without much danger of causing the planet to spiral into that sun's Roche Limit. It thereby would be a useful approximation of a type 1 PMM!

Wanna buy shares in my PMM company?

Jon

 

[DLuckyE]

Well, surely that depends on how picky you want to be? If you would be satisfied with a perpetual motion machine of the second kind, and would accept a few times the age of the universe as perpetuity, then a nice big rocky planet circling a remotely intergalactic white dwarf at say an orbital radius of one light year seems pretty perpetual to me. In fact, if you were not too greedy, you could elaborate on the system slightly and milk it of enough energy to run your PC for longer than a political speech without much danger of causing the planet to spiral into that sun's Roche Limit. It thereby would be a useful approximation of a type 1 PMM!

Wanna buy shares in my PMM company?

Jon

Seeing the amount of energy the moon currently dumps into our planet without changing orbit all that much, i'd say you could safely run more than 1 PC ;-)

 

[Jon Richfield]

Seeing the amount of energy the moon currently dumps into our planet without changing orbit all that much, i'd say you could safely run more than 1 PC ;-)

Weeelllll... I wouldn't want to be greedy, but... let's say my PC plus a comfy condo to live in while using it. After all, it would be a mite chilly living 1 LY from a white dwarf, plus say, 1 million light years from the nearest galaxy.
Fortunately I needn't worry about comms bills; 2 million years response time for each message would be a wee bit on the tedious side for my taste, even just surfing phys forums! :zzz:

 

[sophiecentaur]

Wile E Coyote doesn't subscribe to Newton's Laws of motion. Th Th That's all folks,

 

[Acut]

As my Physics teacher used to say : "You can't save yourself from drowning pulling your hair up".

Just the same principle.

 

[Dale]

Ask your friend to lift himself up. He can't. (Although he can lift someone heavier than himself)

[But if he jumps up, and asks -"how is it possible then" then don't ask me! The question of why people are able to jump has always troubled me! )

Just draw the free-body diagram for each case. It should be crystal clear then.

 

[DaveC426913]

Just draw the free-body diagram for each case. It should be crystal clear then.

That's mean.