# Slingshot thechnology in space travel

I have to drink more to recover from this devostatic embarrashment. I even did not understand momentum although I should have used it myself. Please give me credit for trying, though.:smack:

Yeah, energy can hid in all sorts of different forms, and is often converted to heat. An inelastic collision just means that energy is being converted into some form that we’re not interested in (usually heat). But momentum can’t hide: It’s always obvious, and therefore the obvious momentum is always conserved in collisions.

EDIT: Oh, and don’t be embarrassed. This is quite a common misunderstanding.

Will that magnet still come back and hit that dammned ship?

Chronos , do you know this as a fact, but are you just repeating what you have learnend. This can sound hate talk, but I first keep track of your visions… Dunk as hell

I love Chronos, many typos…

I have personally done experiments on conservation of momentum, and I have read about experiments others have done about conservation of momentum, and I have looked for and failed to find any verified experiment which has successfully refuted conservation of momentum, despite many people trying, and I have seen and worked through mathematical derivations of conservation of momentum from other physical principles, which I have also tested and read of others testing. That’s about as close to “knowing something as a fact” as any mortal can ever achieve.

Did I just insult you? I’m your nro 1 fan.

This must be how Sonny White gets his ideas.

What would be the best way to learn these things? It is over 40 years when I went to school. I still feel that spring force, but instead of rotating a tube, it would be easier to send the ball in a circle. Not quite sober, yet. And Chronos I only read threads you are involved in. So sorry if I did hurt your feelings. Liquer was speeking.

When come back, bring sober.

Noooo!!

I think these propulsion schemes may indeed work - provided everyone aboard the spaceship is drunk. The problem is that when they sober up, they find the ship has reverted to its previous state

What you want is sort of like Wiley Coyote building a cart a magnet in front, and an anvil in the middle. The magnet pulls on the anvil, and the cart moves forward! Except you know that can’t work, because even though the magnet is pulling the anvil forward, the anvil is pulling the magnet backward.

Similarly, imagine you’re floating lost in space. You’ve got a rock and a bungee cord. Aha! You tie the rock to the bungee cord. You throw the rock as hard as you can…and the rock goes flying left, and you move right. Then when the rock stretches out the bungee cord, you reel it in and throw it again, and again. Pretty soon you’re zooming along at a pretty good clip!

The problem with that is that reeling in the rock at the end of the throw exactly cancels out the movement you got from throwing it away in the first place. It doesn’t matter if you’ve got a bungee cord or a rubber band or a steel cable or a really strong magnet. It doesn’t matter how you whip that rock around or in what direction or what speed. When you reel that rock back into your hand you’ll always have exactly the same momentum you started with.

Back in the 80s I remember a Doctor Who ep. (Peter Davison) where he was in outer space without a space suit :rolleyes: swimming in the airless void between his TARDIS and a starship.

To get inside his TARDIS, he pulled a cricket ball out of his pocket, threw it against the starship, and caught the ball after it bounced back…a couple of times.

I was highly tempted to post a link to this - but figured it would just confuse matters.

The sequence is rather fanciful as Gene Cernan would be very happy to tell you. Balancing the entire set of forces and staying even vaguely in control bouncing a ball like that is difficult to believe. But the fundamental physics was there (for a change.)

I thought it was also force.

I could open up a balloon and even though the ejected gas would be trivial the force of the air escaping as the balloon contracts would exert force on me in the opposite direction.

Force = mass x acceleration, so yes, you exert force against the mass you are ejecting; both the mass and the velocity you throw it away at, determine the reaction force.

More generally, and especially for rockets, the rate of change of momentum *is *force.

If he wasn’t in any hurry, a single throw, without even any bounce, would be sufficient. All that multiple bounces and catches did for him was get him into his TARDIS quicker (which may, of course, be important).

Especially since he wasn’t wearing a space suit. :eek:

The multiple throws would also allow him to adjust his trajectory if his first throw didn’t give him exactly the right vector.

–Mark