Measuring Speed of Objects as They Approach You

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Discussion Overview

The discussion revolves around the feasibility and methods for measuring the speed of an approaching object from a stationary position. It includes practical approaches, accuracy considerations, and references to existing technologies.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants propose using hand-held radar guns, as employed by traffic police, to measure the speed of approaching vehicles.
  • Another suggestion involves timing how long it takes for a car to travel between two fixed points (e.g., lamp posts) and calculating speed based on that time and distance, noting that accuracy depends on precise timing.
  • One participant mentions the Doppler effect and police radar as relevant concepts for understanding speed measurement.

Areas of Agreement / Disagreement

Participants express various methods for measuring speed, but there is no consensus on a single best approach or the accuracy of each method discussed.

Contextual Notes

Limitations include potential inaccuracies in timing measurements and the dependence on the observer's ability to identify fixed reference points.

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As a stationary object, is it possible to determine the speed of an object as it approaches you? If so, how? ...and with accuracy?

For instance, if I'm standing on the sidewalk, can I determine the speed of a car on the road as it approaches me?
 
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Physics Novice said:
As a stationary object, is it possible to determine the speed of an object as it approaches you? If so, how? ...and with accuracy?

For instance, if I'm standing on the sidewalk, can I determine the speed of a car on the road as it approaches me?

Sure. Around here the traffic police use hand-held radar guns to catch speeders.
 
Time how long it takes the car to cover the distance between two objects (eg two lamp posts). Later measure the distance between the two lamp posts. Calculate the speed. The accuracy will be limited to how accurately you can measure the time. If the car casts a shadow on the lamp posts as it passes I'd suggest you can get quite an accurate measurement.
 
Physics Novice said:
As a stationary object, is it possible to determine the speed of an object as it approaches you? If so, how? ...and with accuracy?

Some pictures and info to go along with Nugatory's reply: Doppler effect, Police RADAR.
 

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