What sorcery is this!? Science it turns out! This is a great example of Bernoulli’s Principle! In short, this states that moving air has a lower pressure. Imagine trying to dig a hole in a pool of water: as soon as some of the water gets moved out of the way, the surrounding water rushes in to take its place. Air does the same thing!
The cup without any holes in the sides actually holds onto the balloon, which is weird, but makes sense. Inside the cup, air is moving quickly. This causes a lower pressure inside the cup than outside, and air that tries to fill up the space suctions the balloon in place. Alternatively, the cup with holes in the sides allows the surrounding air to help out. Very similar to the Bernoulli Bag, nearby air joins in creating a larger column of air that can lift, and even suspend, the balloon.
Blowing air through a straw makes a small amount of air move pretty fast. A leaf blower makes a lot of air go really fast! When we add the beach ball, this air rushes around it at high speeds, making a low pressure. Surrounding air is then drawn in from all sides, which holds the ball in place.
While it might look like this is just well balanced on a spout of air, this idea falls flat when the angle of the leaf blower is changed. In moving to this orientation, the science stays the same–rushing air still causes the surrounding molecules to rush in and offer support on all sides–despite it looking like magic to the untrained eye!