What concept explains how radar can accurately measure speed in a moving vehicle?

The concept that explains how radar can accurately measure the speed of a moving vehicle is known as the Doppler Effect. This phenomenon occurs when there is a change in frequency or wavelength of waves in relation to an observer moving relative to the wave source. In the context of radar speed measurement, when a radar wave is emitted towards a moving vehicle, the wave reflects off the vehicle and returns to the radar unit. If the vehicle is moving toward the radar, the returning wave's frequency increases; conversely, if the vehicle is moving away, the frequency decreases.

By calculating the shift in frequency between the emitted and received waves, the radar device can determine the speed of the vehicle with a high level of accuracy. This relationship between the speed of the vehicle and the frequency shift is what makes the Doppler Effect a crucial principle in radar technology. Other options like Newton's Law of Motion or Gravitational Pull are not directly involved in the mechanism of radar speed measurement, while Thermal Expansion does not pertain to the measurement of speed at all. Thus, the Doppler Effect is the foundational concept that allows radar units to function effectively in speed detection tasks.