How strong is the air pressing down on you right now? Air has weight. The atmosphere above you pushes down with real force. Two simple tests show that force in action. You fill a plastic bag with air and tie it over a jar's opening. Press down on the inflated bag. It pushes back, just like an air mattress. Next, place an empty bag inside the jar and fold its edges over the rim. Tie it tightly. Try pulling the bag out. The full weight of the atmosphere presses the bag down. No one can lift that much air.