Force from the Coanda effect

A fluid jet curvature around surfaces generates a force capable of moving or lifting things. This is a beautiful demonstration of Newton's third law.
Additional comment (for advanced students).
The last demonstration with the ball in the air stream requires a comment. Often this effect is explained as follows. Let's look at the situation where the air flows mainly around the ball from one side. The air velocity on that side of the ball is said to increase. From the Bernoulli equation, we know that an increase in jet velocity means a decrease in (static) pressure and therefore the ball is pushed towards lower pressure. Such an explanation must leave us unsatisfied. It is not clear why the air flows around the ball and not, for example, bouncing off the ball. The clinging of the stream to the surface of the ball is the Coanda effect. Then, it is not obvious why the air velocity increases as it passes around the ball. It is true, but it requires a serious explanation. Bernoulli's equation is correct, but it is rather complicated to refer to it in this demonstration. If one wants to interpret this effect in terms of pressures, one should start by observing that the airflow is curving, which means that we have a pressure gradient. This is a topic for a separate lecture.