Newton's first law of motion: Objects in motion will stay in motion and objects at rest will stay at rest, unless acted on by a. friction
b. acceleration
c. unbalanced force
d. contact force

Newton's first law states that every object will remain at rest or in uniform motion in a straight line unless compelled to change its state by the action of an external force. This is normally taken as the definition of inertia

if the thermos has a vacuum innner, then heat through conv currents and conduction are reduced = vacuum flask

54 degrees incident angle = reflected angle

angle is from normal turned to line of ray