A balloon filled with helium or hot air can float in the atmosphere. A balloon filled with air from your lungs falls to the ground when it is released. Why do these balloons behave differently?
Air and gases, like water are fluids. Both balloons are in a fluid yet behave differently because of density. The balloon filled with helium or hot air is less dense that the air in the atmosphere. An object that is less dense than the fluid will float. The balloon filled with air from the lungs falls to the ground slowly because the balloon is denser than the air.