The speed at which any planet moves through space is constantly changing. In a perfectly circular orbit, the orbital radius of the planet would be constant and therefore so would be its observed angular velocity. In elliptical orbits, the angular velocity varies. In elliptical orbits, the orbital radius of the satellite will vary and therefore so will its angular velocity. The planet travels "faster" (greater angular velocity) when closer to the Sun, then "slower" (less angular velocity) at a more distant radius.

According to Newton's 2nd Law, what is the underlying force behind this change in velocity?
A) Mass
B) Gravity
C) Friction
D) Projectile motion

In elliptical orbits, the orbital radius of the planet will vary and therefore so will its angular velocity. The planet travels "faster" (greater angular velocity) when closer to the Sun, then "slower" (less angular velocity) at a more distant radius.

The force of gravity is greatest when a planet is closer to the Sun. Consider F = ma; if mass is constant and F increases, then acceleration must increase as well.