sentences:  Compressed air enters an airbag shaped like a torus, and when the bag is filled it creates an airtight seal with the ground, and forces more air into the center of torus, eventually causing the air to flow over the bag and to raise the load above the ground.The compressed air is forced under the airbag, pushing it and the load less than a millimeter off the ground.Because air casters are virtually friction-free, the force required to move them is very low, often around one to five lbs.