This is an Example of a Non-Newtonian Fluid where the cornstarch formed a network of long chains. If a quick force is applied to the cornstarch solution the cornstarch cannot move as quickly so it stays stiff like solid.
Rocket Cup
The alcohol inside the empty can combust and heats up the air inside. The heated air molecules move faster and collides to each other, increasing the air pressure inside, forces the styrofoam cup to shoots up.
Anti-Gravity Water
The screen net holds the water inside the cup despite of the removal of the cardboard because of the high surface tension of water, The water clings instead of falling through.
Electromagnet
When you attach the wire into the battery, electrons flow into the wire and to the nail which is also known as solenoid and it creates a magnetic field that concentrates inside the coil that creates a powerful magnetic effect called "Electromagnet".
Needle Floating
When you put the needle on to the water it floats because of surface tension which creates intermollecular forces and the water molecules in the surface are pulled in by the cohesive force and thus have higher potential energy that keeps the water surface in balance.