In July 1994 the comet shoemaker-levy 9 collided with the planet Jupiter, as scientists had predicted. To be able to accurately predict when a comet will collide with a planet, it is essentially understand -

the gravitational attraction that exists between all bodies

Explanation:

Comet shoemaker-levy 9 was the comet that broke away and collided with the largest planet on our solar system, the Jupiter. The comet fall apart from the asteroids in the year 1992 and flew and hit Jupiter in the year 1994. This was predicted by the scientist.

Similarly when a comet can hit a planet can be accurately predicted by the scientist or the researcher by understanding and studying the gravitational forces that exists between the bodies in the solar system. It is very important to understand the gravitational attractions which exists between all the bodies in the universe in order to calculate or predict when can a comet collide with a planet.

in 1783 cavendish was working with his hydrogen gas and found that when he burned it and condensed the vapor it was water. this was very significant since it disproved the greek theory of elements completely since water was not a simple substance but the product of two gases. it was lavoisier who hearing of the experiment gave cavendish's gas the name hydrogen ("water-producer") and added that hydrogen burned by combining with oxygen and that water was a hydrogen-oxygen combination.

explanation: