Press the clay down into the bottom of the jar with your thumb. Cover most of the bottom of the jar with the clay by smushing it around, making sure that it slightly sticks to the glass.
Fill the jar half-way with cold tap water and then add at least 3 drops of the red food coloring into the water. Stir the food coloring and water until the water is thoroughly mixed and becomes light red in color.
Place the straw into the jar, sticking the bottom end of the straw into the clay. Make sure the straw can stand up after being stuck in the clay.
Pour out the water in the jar by completely turning over the jar face down over a sink. After a couple of seconds, turn the jar back right side up and place it on a table.
Try and look for any remaining liquid. There should be colored liquid in the straw filled up half-way as the water in the jar was. This is due to the water molecules being attracted to one another when reacting to the air in the straw pushing the water up. Thus, an antigravitational force is created in the straw.