1. Gravity: This is the most obvious force, as it pulls everything towards the center of the Earth. The rocket needs to generate enough thrust to overcome this downward pull.

2. Air Resistance: As the rocket moves through the atmosphere, it encounters friction from the air. This resistance increases with speed and can become a significant force, especially at lower altitudes.

Here's a breakdown:

* Gravity: This force depends on the mass of the rocket and the strength of the gravitational field. It's a constant force acting directly downwards.

* Air Resistance: This force is more complex and depends on factors like the rocket's shape, speed, and the density of the air. It increases with speed and acts in the opposite direction of the rocket's motion.

To successfully launch, a rocket's engine needs to produce enough thrust to overcome both gravity and air resistance. The thrust is a force generated by the engine's combustion and exhaust. It needs to be greater than the combined forces of gravity and air resistance to propel the rocket upward.

Once the rocket reaches a high enough altitude, the air resistance becomes negligible, and the primary force it needs to overcome is gravity. However, even in the vacuum of space, the rocket still needs to continue generating thrust to maintain its speed and altitude.