An empty office chair is at rest on a floor. consider the following forces: . 1. a downward force due to gravity; . 2. an upward force exerted by the floor; and. 3. a net downward force exerted by the air. which force(s) act on the office chair? . 1. none of the forces act on the chair since. it is at rest. 2. all three forces. 3. 1 only. 4. 1 and 2 only. 5. 2 and 3 only.