How do we stay on the ground

Which of the following is not a physical property of mattera. melting pointb.heat of combustionc. viscosityd. boiling point

Ablue car pulls away from a red stop-light just after it has turned green with a constant acceleration of 0.5 m/s 2 . a green car arrives at the position of the stop-light 6.5 s after the light had turned green. if t = 0 when the light turns green, at what time does the green car catch the blue car if the green car maintains the slowest constant speed necessary to catch up to the blue car? answer in units of s.

Are formed where bumps from two surfaces come into contact ?