1. Gravity: This is the constant force pulling the rocket back towards the Earth. The stronger the gravitational pull, the more it will slow the rocket down.

2. Air Resistance (Drag): This force opposes the rocket's motion through the atmosphere. The denser the air, the more resistance the rocket experiences. This force is significant during the initial launch phase and decreases as the rocket climbs higher into thinner air.

It's important to note that these forces are constantly working against the rocket's engines, which are pushing it forward. The balance between the forces determines the rocket's acceleration and ultimately, its trajectory.