Gravitation, Science I Revision, Fill in the blanks.

Gravitation
1. The orbit of a planet is an ellipse with the Sun at one of the foci.
2. According to Newton's first law, mass is the measure of inertia of an object.
3. True free fall is possible only in vacuum.

4. An object going vertically upwards will be free from the gravitational influence of the earth, it its initial velocity is equal to escape velocity of the earth.