Thrust Direction: Upward vs Downward

What is the difference between upward thrust and downward thrust?

Which forces are involved in each direction?

Answer:

Upward thrust refers to a force that pushes an object upwards typically by exerting a downward force on the environment, as seen in birds and airplanes. Downward thrust refers to a force that pushes downwards, such as a rocket launching by expelling gases in the opposite direction. This is due to Newton's third law of motion.

The terms upward thrust and downward thrust refer to the directionality of the force exerted. Upward thrust refers to a force that pushes an object upwards. This is seen in helicopters, for example, which create lift (upward force) by pushing air down, thus experiencing an upward reaction force in accordance with Newton's third law.

Similarly, birds and airplanes fly by exerting force on the air in a direction opposite to the direction they want to go. For instance, their wings force air downwards and they move upwards and forwards as a reaction. On the other hand, downward thrust is a force applied downwards. An example of this would be a rocket launching. In this case, the rocket expels gas backwards at a high velocity causing a reaction force that propels the rocket forward and upwards (opposite to the direction of the expelled gases).

To summarize, the direction of thrust is contingent on the direction of the force exerted by the object. This force is generally applied in the opposite direction to the one the object wants to move according to Newton's third law of motion.