which is accurate? Camera, car spedo, sat-nav?

[Bengali]

I notive that the speed on my Sat Nav is lower than on my car spedo. I assume that the Sat nav is tyhe more accurate because it calculates movement over the ground. Hills will bring in inaccuracy perhaps. My car speedo will vary as the tyres wear and their effective diameter and therfore circumference changes. Which should I use?
By the way; speed is the average of velocity, to be very simple and as it is mathematically incorrect to try to have an average of averages, how can specs register "average speed". Surely they measure SPEED. ie The distance travelled and the time taken( Miles per Hour)
Another thought. If speed is the problem in a particular place and it is a danger it should be stopped. If a camera is installed and it registers speeders it is not doing its job. The only successful cameras are those that don't earn. Those that earn are failing and a better method should be found. Perhaps we should have a man with a red flag walking in front. Why did that stop?

[GerryC]

Questions, questions. Welcome to the forum.

Satnavs calculate the speed based on the distance travelled between receiving timed position updates. Car speedos generally take it from some engine part. The important thing is that it must NOT show under-speed and can show over-speed upto 10% (I think). Tyre wear etc is an important part of this.

Which to use? Well, the speed limit is a speed you should not go over but can be under it. For this reason, I usually go by the car speedo.


Normal cameras capture the distance travelled in 1/2 a second (set time, variable distance). The difference with Specs is that it does this twice some distance apart (set distance, variable time). Knowing this distance and the time it took you to get from one to another gives the "average" speed through the section. This is to stop sudden braking for a camera then speeding up again.


I won't go into accident blackspots but the man with a flag ended when cars could manage to go at more than walking pace.
_________________
Gerry
TomTom730T
Cameralert for Android
Brodit ProClip mount

[PaulB2005]

[peterc10]

Wikipedia is our boring friend.

http://en.wikipedia.org/wiki/Velocity

Here

BTW how can I put in a hyperlink to a word in this forum?

Edit to add hyper link - Mike Alder
_________________
Peter
HTC Sensation
Sygic GPS for Europe (No more TT "support"!)
Copilot for USA
Bury CC9060 bluetooth car kit & Brodit mount

[mikealder]

Peter, click the edit button on your post and you will see what I did, I left the original there for you to spot whats different - Mike

[peterc10]

[MaFt]

peter - simply type the following:

[peterc10]

[mikealder]

I only type the [url= and then hit CTL V to paste the link URL in to the text followed by Here [/url]
Note I will have put the target URL on the clipboard usually with a double click to hichlight it and pressing CTL C

Then I double click the word "Here" and hit the B button to make it BOLD and repeat click the "Here" then use the Font Colour box to select the red (not really necessary as the forum code can do this on its own but old habits etc, etc With practice it takes only a few seconds - Mike

[AliOnHols]

[M8TJT]

Yes. The direction is changing, so the velocity is changing so there is an acceleration towards the instantaneous centre of the turn. This is usually called (wrongly) centrifugal force.

[DennisN]

WOT?????

I woz just gonna answer the OP with "Yes" Now I'm struggling to decide how many beans make five.
_________________
Dennis

If it tastes good - it's fattening.

Two of them are obesiting!!

[MaFt]

we're drifting off-topic here...

[BigPerk]

Yes, although it has to be said that it went off topic straight after bengali's own first paragraph !

I remember seeing a thread a month or so back answering this same question - it seems to be a topic second only to 'why haven't I got life membership?'
_________________
David
(Navigon 70 Live, Nuvi 360)

[GerryC]

Bengali, Please don't be put off by the comments on this thread - it's nothing personal. Sometimes, someone just says something that gets a conversation going. Please feel free to respond to the thread or any others that take your fancy.

Gerry

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