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You're in a car. The speedometer reads 50mph. How fast are you going?
by blhack 6y ago
You're in a car. The speedometer reads 50mph. How fast are you going?
- Chris2048 6y agoYou're in a rocket-ship, the speedometer reads 0.5c (half-lightspeed); How fast are you going? If you understand you'll ask "from what frame of reference?"
- AlexTWithBeard 6y agoI wonder... If there were such a speedometer what would it use as a reference in real life? Earth? Sun? Sag A?
- rtkwe 6y agoMost useful in space depends a lot on what you're doing at the time. Docking with small separation? Velocity relative to target. Orbiting something? speed relative to that body. Traveling between stars? Tougher but most likely relative velocity towards your target since your path is going to be relatively linear?
- icedistilled 6y agoBut you can easily answer "I'm going 0.5c from the frame of reference the speedometer uses"
- Chris2048 6y agoBut the point is you need to understand what speed is.
- klyrs 6y ago50, plus or minus a bit depending on environmental conditions, tire wear, and speedometer calibration, relative to the surface you're driving on.
- nlitened 6y agoNot really if the car is running on a treadmill installed by a foreign government.
- klyrs 6y agoI covered that. "The surface you're driving on" in this case would be the belt of the treadmill.
- nlitened 6y agoOk you’re right. But you haven’t covered the case when the speedometer is lying :)
- klyrs 6y ago"Lying" or miscalibrated? Because I did mention calibration. My speedometer is the mechanical sort, because I drive an old beater. It's incapable of complex deception. If I was paranoid, I could easily verify that the cable is connected to the gearbox appropriately, and trace it up to my instrument panel in about 20 minutes.
- Lammy 6y ago"It doesn't matter, as long as enough other people agree that 50mph means the same thing."
- oxygenjoe 6y agoToo fast for the city, too slow for the highway. 50mph is a compromise that nobody wants