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Gravity

The less gravity something has, the more its mountains can grow.

  • for this reason, the moon is bumpier than the Earth, relative to its size.
  • Also for this reason, asteroids can be egg shaped.

Gravity Assist

A close terrestrial analogy is provided by a tennis ball bouncing off the front of a moving train. Imagine standing on a train platform, and throwing a ball at 30 km/h toward a train approaching at 50 km/h. The driver of the train sees the ball approaching at 80 km/h and then departing at 80 km/h after the ball bounces elastically off the front of the train. Because of the train's motion, however, that departure is at 130 km/h relative to the train platform; the ball has added twice the train's velocity to its own.

  • Translating this analogy into space: in the planet's frame of reference, the spaceship has a vertical velocity of v relative to the planet. After the slingshot occurs the spaceship is leaving on a course 90 degrees to that which it arrived on. It will still have a velocity of v, but in the horizontal direction. In the Sun reference frame, the planet has a horizontal velocity of v, and by using the Pythagorean Theorem, the spaceship initially has a total velocity of āˆš2v. After the spaceship leaves the planet, it will have a velocity of v + v = 2v, gaining around 0.6v.

Newton's Second Law

A body will accelerate at a rate that is proportional to the force

  • ex. If a car doubles in weight, you must double the force provided by the engine to make the car go the same speed. Also, the acceleration would be twice as great if the force was also twice as great.
  • this law also applies to the observation that 2 different objects of vastly different masses fall at the same speed. A body of twice the mass of another will have twice the gravitational pull on it. However, since the mass is doubled, the object will also require twice the amount of force to pull it to the earth, effectively cancelling each other out. The result is that both objects have the same acceleration.
  • repulsive gravity ( look it up)