# Is this possible?

#### quietrain

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#### Doc Al

Mentor
What do you think?

#### quietrain

to tell the truth, i don't know :(

#### Ryan_m_b

Staff Emeritus
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?

#### Doc Al

Mentor
to tell the truth, i don't know :(
Consider the net force on the system.

#### quietrain

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?

#### Ryan_m_b

Staff Emeritus
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)?

#### quietrain

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?

#### Ryan_m_b

Staff Emeritus
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

#### quietrain

ah i see...

so theres no way that internal forces can ever make the system do work? only an external can?

thx

#### Ryan_m_b

Staff Emeritus
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.

#### Doc Al

Mentor
ah i see...

so theres no way that internal forces can ever make the system do work? only an external can?
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.)

#### e2m2a

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.

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