Final answer:
The propelling of the balloon when Angela releases the air demonstrates Newton's third law of motion, where the expulsion of air in one direction propels the balloon in the opposite direction.
Step-by-step explanation:
When Mover Angela blows air into a balloon and holds the end of it closed with her fingers, and then lets go, the balloon is propelled by the release of the air inside. This is a demonstration of Newton's third law of motion, which states that for every action, there is an equal and opposite reaction. When the air is expelled out of the balloon in one direction, the balloon itself is propelled in the opposite direction. This is similar to how rockets move forward by expelling gas backward at high velocity, known as thrust, or how birds fly by pushing air downward and backward to get lift and move forward.