Radar guns are used to measure the speed of moving objects. Radar guns work by projecting radio waves of known frequencies onto moving objects.

How is a radar gun able to calculate the speed of a moving object using radio waves?
A.
Radio waves are diffracted by the moving object, which causes a change in wave speed that can be analyzed by the software of the radar gun to calculate the object's speed.
B.
Radio waves are refracted by the moving object, and the angle of refraction of the waves can be analyzed by the software of the radar gun to calculate the object's speed.
C.
Radio waves are absorbed by the moving object, which causes an increase in the temperature of the object that can be analyzed by the software of the radar gun to calculate the object's speed.
D.
Radio waves are reflected off of the moving object, which causes a change in frequency that can be analyzed by the software of the radar gun to calculate the object's speed.