- #1
quietrain
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Can this be Done? | Solutions to Uncertainty
- Thread starter quietrain
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Discussion Overview
The discussion revolves around the feasibility of using internal forces, specifically involving magnets and springs, to propel a car forward. Participants explore concepts related to Newton's laws, internal versus external forces, and the implications of these principles in a mechanical system.
Discussion Character
- Exploratory
- Technical explanation
- Debate/contested
Main Points Raised
- Some participants express uncertainty about the possibility of achieving motion using internal forces, with one stating, "to tell the truth, i don't know."
- One participant argues that magnets pulling towards each other would prevent motion, comparing it to the impossibility of flying by pulling one's feet up.
- A proposal is made to install a spring to create a jerking motion of an outer magnet, suggesting this could generate a forward net force.
- Another participant questions the outcome of adding a spring, prompting consideration of the forces at play when the spring is compressed and released.
- Concerns are raised about the principle of action and reaction, indicating that any forward motion would be countered by an equal backward force from the magnets.
- Participants discuss the necessity of external forces to achieve work on the system, with one stating that internal forces will cancel out and cannot do work.
- References to Newton's laws and conservation of linear momentum are made to support the argument that only external forces can change the speed of the system's center of mass.
Areas of Agreement / Disagreement
Participants generally agree that internal forces cannot produce net work on the system, but there is ongoing debate about the mechanics involved and the implications of using springs and magnets.
Contextual Notes
Limitations include assumptions about the behavior of springs and magnets in a mechanical system, as well as the dependence on definitions of internal and external forces. The discussion does not resolve the complexities of these interactions.
- #2
Doc Al
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What do you think?
- #3
quietrain
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to tell the truth, i don't know :(
- #4
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No because the magnets are pulling towards each other, to put it another way; have you ever tried to fly by reaching down and pulling your feet up?
- #5
Doc Al
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Consider the net force on the system.quietrain said:
- #6
quietrain
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what if i install a spring at the top right corner of the holder, such that i can swing the outer magnet outwards anticlockwise,
like using the spring to produce a jerking circular motion of the outer magnet outwards,
will i be able to now cause the car to move forward abit?
since now the net force is +ve forward?
like using the spring to produce a jerking circular motion of the outer magnet outwards,
will i be able to now cause the car to move forward abit?
since now the net force is +ve forward?
- #7
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If you put a spring on the top right what do you think will happen? Consider A) the bottom of the arm has a magnet near a magnet and B) what happens when you hold a spring at arms length facing down (does it oscillate forever)?
- #8
quietrain
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well, the forever part can come later, but for now, i am thinking of this type of spring,
so maybe i can make use of the stored force when the spring is compressed , and then "release" the compressed spring so that i jerk the outer magnet arm forward.
it will now cause the car to move forward?
so maybe i can make use of the stored force when the spring is compressed , and then "release" the compressed spring so that i jerk the outer magnet arm forward.
it will now cause the car to move forward?
- #9
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- 727
No matter what you do you every action has an equal and opposite reaction
If you jerk the arm anticlockwise it will exert a backwards force equal to that of the forward force. The rear magnet is pulling the front magnet back remember
If you jerk the arm anticlockwise it will exert a backwards force equal to that of the forward force. The rear magnet is pulling the front magnet back remember
- #10
quietrain
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ah i see...
so there's no way that internal forces can ever make the system do work? only an external can?
thx
so there's no way that internal forces can ever make the system do work? only an external can?
thx
- #11
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Visualise it this way, if you and me were in space connected by a /\ shaped beam and joined hands to pull at each other would we fly through space? No, we would just put force on the beam connecting us. Even if one of us pulled harder than the other the effect is the same.
Some energy or mass has to leave the system I.e. exhaust from a rocket. Look up Newtons laws, that should explain it all.
Some energy or mass has to leave the system I.e. exhaust from a rocket. Look up Newtons laws, that should explain it all.
- #12
Doc Al
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I'd put it this way: The only way to accelerate the system is by using an external force. (Internal forces will just cancel out.)quietrain said:
- #13
e2m2a
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Also, check out the conservation of linear momentum and Euler's First Law. The man, car, and 2 magnets in your diagram constitute a system. The system has a center of mass.
Essentially, Euler's First Law states that only an external force acting on a system can change the speed of the center of mass of a system.
Essentially, Euler's First Law states that only an external force acting on a system can change the speed of the center of mass of a system.
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