How Does the "sling Shot" Effect Work?

The Juno Probe is about to become "The Fastest Man-Made Object in History" by using a "Gravitational Sling-Shot Effect" to gain some sort of advantage and achieve this maximum velocity. QUSESTION: Basic terrestrial Newtonian Intuition tells me that one cannot drop a ball (not even a Superball, in a vacuum) and have it bounce to a height that is greater than that of release. When an automobile travels up and down a series of hills and valleys, nothing is gained, in the terms of energy-vs-altitude ... SO ... How is any advantage gained by passing closer to a gravitational bodt ? ... I can only think of Roller-Derby moves and the school-yard game of Crack-the-Whip but I am still wondering how this maneuver would gain a FUEL ADVANTAGE, over a straight-burn ... How can you keep gaining more velocity without using as much fuel as a strait-burn ? ... This seems to DEFY CONSERVATION OF ENERGY, NO ? ... WHY< THEN ? have we solved ZERO POINT ENERGY ?
- Frank Langham (age 54)
AUSTIN, TX USA

The 'sling shot effect' is very real and, not to worry, energy and momentum are conserved,   Here is a simple example:   suppose you are riding a bicycle down the road at 5 mph.  You encounter a large car coming toward you at 10 mph.  There is a big spring in front of the car that you bounce off of and you go backwards with essentially the same speed as the car, plus your own recoil velocity.  So you have changed your velocity from +5mph to -15mph,  Granted, you won't last very long going 15 mph in reverse on a bicycle. The same thing happens in space rocketry.    You might worry about the conservation of momentum: the car will actually slow down just a tad.  The amount will be proportional to the ratio of your mass to that of the car. 

Take a look at a Scientific American article at   or just google 'sling shot effect' for lots of information and details.

 

LeeH

(published on 10/10/2013)