# The transference of potential energy to kenetic energy and it's effect on momentum

carl fischbach

## Main Question or Discussion Point

Lets say that you take an ultra modern spacecraft
like Nasa is researching or may already have and
equip it with a vast potential energy storage
system.Before you embark on your flight a large
quantity of potential energy is stored on board
the ship.The craft is now accelerated to 50% of c
in a straight line.Now we can agree that the craft
possesses momentum x.The ship is travelling at 50%
c and the vast quantity of potential energy,stored
before the fight,is converted to very high speed
particles stored in a ring on board the ship.
Lets say the ships mass has increased by 20%,due
to the conversion of potential energy to kenetic
energy.The ship now possesses momentum y.If you
decelerate the ship in straight line you now have
an imbalanced force*time relationship between
acceleration and deceleration.
There are several possible explanations, the ship
slows when potential energy is converted to
kenetic energy,stored potential energy acts like
mass,the ship does not act heavier when gaining
kenetic energy, or something I've overlooked here.

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chroot
Staff Emeritus
Gold Member

Wow, there really are a lot of misconceptions about special relativity packed into this paragraph. Let's see if we can begin to sort them out.
Originally posted by carl fischbach
and
equip it with a vast potential energy storage
system.
You mean -- fuel?
The craft is now accelerated to 50% of c
in a straight line.
0.5c relative to the stationary earth, I imagine.
Now we can agree that the craft
possesses momentum x.
Momentum depends on the observer. If "we" means specifically "observers on the earth," then sure, we'll call it x.
The ship is travelling at 50%
c and the vast quantity of potential energy,stored
before the fight,is converted to very high speed
particles stored in a ring on board the ship.
Er, okay.
Lets say the ships mass has increased by 20%,due
to the conversion of potential energy to kenetic
energy.
Why should we say this? Where did this 20% figure come from? What sort of potential energy are we talking about?

- Warren

russ_watters
Mentor
My understanding was that energy is proportional to mass regardless of the form of the energy - stretch a rubber band (for example) and it gains mass.