While holding the cardboard in place, turn the glass upside down, and then remove your hand. The cardboard should stick to the glass because the air pressure underneath the cardboard is exerting more pressure on the cardboard than the weight of the water. Put a lighted candle on a plate, place the candle and the plate in a pan with about an inch of water, and invert a clear glass over the candle. The candle should go out after it uses all of the oxygen inside of the glass and water should get sucked into the glass since the air pressure inside of the glass is less than the air pressure outside of the glass. The pencil should appear broken where the water and the air intersect, at the top of the water, because of the refraction of light due to the two different mediums.
Light is bent when it passes from one medium such as air, into another, such as water.
Have a friend slowly fill the cup with water. You should be able to see the coin by the time the cup is filled because of the refraction of light as it travels from the water, to the air, to your eyes. The reason you are able to stand-up is because the floor pushes you up with just as much force as you push down on the floor. The forces are balanced. Try to stand on water.