Coming in contact with the surrounding atmosphere at high rates of acceleration would challenge the structural integrity of the vehicle, would induce enormous drag and heat the skin of the craft to glowing temperatures, but perhaps the UFO does not come into direct contact with the atmosphere, but actually repels the atmospheric boundary layer surrounding its form. This would account for how they can move quickly without encountering air resistance and thermal stress. Structural integrity is a major factor in aircraft design and construction. No production airplane leaves the ground before undergoing extensive analysis of how it will fly, the stresses it will tolerate and its maximum safe capability. Every airplane is subject to structural stress.
Stress acts on an airplane whether on the ground or in flight.
Stress is defined as a load applied to a unit area of material. Stress produces a deflection or deformation in the material called strain. Stress is always accompanied by strain. Current production general aviation aircraft are constructed of various materials, the primary being aluminum alloys. Rivets, bolts, screws and special bonding adhesives are used to hold the sheet metal in place.