[Sarahisme]

I was just reading up on the Slingshot effect, and was wondering where the energy comes from for the increased velocity of the "slingshotted" object?

Cheers :)

Sarah :)

[Spyman]

Sarahisme said:

I was just reading up on the Slingshot effect, and was wondering where the energy comes from for the increased velocity of the "slingshotted" object?

From the momentum of the object causing the slingshot.

If You throw a ball against a car moving towards You the ball returns with it's own speed + the cars speed and the car slows down a little when hit by the ball.

[Ophiolite]

As a consequence the object that has provided the additional velocity will now rotate very slightly more slowly. In practical terms we could slingshot spaceshuttles around Jupiter five times a day for the next thousand years and still not be able to detect the this reduction, but it would be there.

[Sarahisme]

what about gravitational potential energy?

[swansont]

Sarahisme said:

what about gravitational potential energy?

Can you be more specific? What about the potential energy is your concern?

[swansont]

Ophiolite said:

As a consequence the object that has provided the additional velocity will now rotate very slightly more slowly.

Revolve, not rotate. The energy, AFAIK, comes from the orbit, not the rotation.

[Spyman]

Sarahisme said:

what about gravitational potential energy?

I don't now exactly what You mean here ?

But as in Ophiolite's example: Jupiter revolves very slightly more slowly around the Sun and as a consequence of that it will be pulled a little, tiny, puny bit closer to the Sun, thus loosing gravitational potential energy relative the Sun, and the spaceshuttle can use the new speed to gain it.

[Sarahisme]

hmm ok well the situation i was thinking of was a simplified version, that is neither object is rotating (like a planet would for example), so then yeah, what about for that kind of situation?

[Spyman]

Sarahisme said:

hmm ok well the situation i was thinking of was a simplified version, that is neither object is rotating (like a planet would for example), so then yeah, what about for that kind of situation?

I hope You have read swansont's note about "revolve" is a better word than "rotate".

If You have only Two objects then there is no slingshot effect, the objects will move apart with the same speed they moved against relative eatch other.

The slingshot effect is gained from a third frame, in empty space with just Two objects it can't be measured.
The example I gave with the car and the ball shows this, the ball moves against the car with the same speed it moves apart from the car, after the hit, relative the car. But relative You, the thrower and the third frame, the ball returns with throwing speed plus car speed.

Thus there is no trade of gravitational potential energy between these Two objects either, without the third frame.

[swansont]

Quote

I hope You have read swansont's note about "revolve" is a better word than "rotate".

But did you? ;) :-) (IOW, you need to go back and edit post #7)

[Johnny5]

Sarah, do you mean gravitational boost?

[Sarahisme]

lol sorry i missed swansont's post :P

[Sarahisme]

oh ok i mean more a system with 2 objects in it. with a small one and a big one, and you move the smaller one towards the bigger one at a certain velocity (simplified system sort of thing)

[Sarahisme]

Johnny5 said:

Sarah, do you mean gravitational boost?

whats that exactly? :)

[Johnny5]

Gravitational Boost

It's a trick used by NASA to save money in rocket fuel, during launch, or as you can see in the lower diagram, a large body can be used to alter the trajectory of a ship or what have you.

[Spyman]

swansont said:

But did you? ;) :-) (IOW, you need to go back and edit post #7)

OK Have done that ! :-)

Actually we posted at the same time so I didn't read Your post until after mine was posted and then I just figured I still could use "rotate around the Sun" anyway - bad decision, huh... :embarass:

[Spyman]

Sarahisme said:

oh ok i mean more a system with 2 objects in it. with a small one and a big one, and you move the smaller one towards the bigger one at a certain velocity (simplified system sort of thing)

Please, read my post #9 again.

Spyman said:

If You have only Two objects then there is no slingshot effect, the objects will move apart with the same speed they moved against relative eatch other.

[Sarahisme]

are you sure? (you probably are right of course, but i am just checking more for myself...) what abot a giant planet with a space ship acclerating or moving towards it, then do you get an increase in KE of the spaceship and thus a slingshot effect?

[Spyman]

Sarahisme said:

are you sure? (you probably are right of course, but i am just checking more for myself...) what abot a giant planet with a space ship acclerating or moving towards it, then do you get an increase in KE of the spaceship and thus a slingshot effect?

If You bounce a ball against a wall it won't return with higher KE.

The spaceship gets an increase of KE when moving towards the planet but then loses the same amount when moving away, relative the planet.

It is only in a third frame the slingshot effect can be measured and You can have an increase or decrease of KE, stolen from or given to the planet, relative the third observers view.

This means there has to be another person on a third object, either a second spaceship or a second planet to measure the slingshot, relative him/her, or a third object in space, the person in the spaceship or on the planet can use to measure the slingshot with, relative it.

[Sarahisme]

ok then you there is a 3rd object(an observer)