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2002 MG TF VE51FTF
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Discussion Starter · #1 ·
As a very young man (now 68) I used to read a lot of car mags and I remember reading an article (Hot Car Mag?) about using a house brick as a crude brake tester (decelerometer). It depended on how you laid the brick down on edge in the footwell ie frog facing fwd or back and relied on the braking force needed to tip it forwards. Foolishly I mentioned this to mates in the pub who think I'm stark staring mad, searched the web and can't find anything on it.
Did I dream it, can someone please confirm I'm not completely ga ga
 

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Starlight Silver MG TF 135
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191 Posts
Can't help with the magazine date etc., but I am sure you are right! I remember being told the same story by a mechanic who was trying to advise how to do a test in preparation for an MOT on my first car (Wolseley 1500 with brake which could be described a s "Adequate" if you were feeling generous!): The perfect first car, with hindsight, as it taught me to look well ahead down the road, anticipate hazards and lift-off early.

As regards the basic principle: There was a company (still exist I think) called First Inertia Ltd. I sold Aluminium castings to back in the 1970's. The relevance is that one of their products was an Inertia Switch for crash detection (to stop electric fuel pump etc.) The design principle was a Steel ball in held into a matching hemispherical "dish" by a magnet. The steel ball made a circuit by connecting two (otherwise insulated) sides of this dish. By adjusting the strength of magnet and (presumably) the spacing of magnet below the ball, the G force required to move the ball and break the circuit, could be adjusted.

I guess that it is obvious that a "Frog forward" brick would need more G load to fall forward than a "Frog-to-the-Rear" Brick.
 

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97 BRG MGF. 2009 SKODA SUPERB.
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492 Posts
Can't help with the magazine date etc., but I am sure you are right! I remember being told the same story by a mechanic who was trying to advise how to do a test in preparation for an MOT on my first car (Wolseley 1500 with brake which could be described a s "Adequate" if you were feeling generous!): The perfect first car, with hindsight, as it taught me to look well ahead down the road, anticipate hazards and lift-off early.

As regards the basic principle: There was a company (still exist I think) called First Inertia Ltd. I sold Aluminium castings to back in the 1970's. The relevance is that one of their products was an Inertia Switch for crash detection (to stop electric fuel pump etc.) The design principle was a Steel ball in held into a matching hemispherical "dish" by a magnet. The steel ball made a circuit by connecting two (otherwise insulated) sides of this dish. By adjusting the strength of magnet and (presumably) the spacing of magnet below the ball, the G force required to move the ball and break the circuit, could be adjusted.

I guess that it is obvious that a "Frog forward" brick would need more G load to fall forward than a "Frog-to-the-Rear" Brick.
I don't doubt the First inertia story, but a brick?? Come-on you two you'll be saying pigs fly next.:ROFLMAO:
 

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2002 MG TF VE51FTF
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413 Posts
Discussion Starter · #6 ·
Thank you Ellisjo now that's me you and some anonymous mechanic not quite a majority but getting there.
Musing on this and dredging my memory I also seem to recall a cheap plastic thingy where ball bearings rolled up slopes of various degrees and off the edge, slam your brakes on and see what you scored. Probably highly inaccurate but like First Inertia the physics is sound, that is until you get to the quantum level where all bets are off.
D4KGP shame on you have you never seen the hot air pig balloon or a police helicopter, you'll be saying next Santa doesn't exist and he's promised me a brake testing brick this year.
 

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97 BRG MGF. 2009 SKODA SUPERB.
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Thank you Ellisjo now that's me you and some anonymous mechanic not quite a majority but getting there.
Musing on this and dredging my memory I also seem to recall a cheap plastic thingy where ball bearings rolled up slopes of various degrees and off the edge, slam your brakes on and see what you scored. Probably highly inaccurate but like First Inertia the physics is sound, that is until you get to the quantum level where all bets are off.
D4KGP shame on you have you never seen the hot air pig balloon or a police helicopter, you'll be saying next Santa doesn't exist and he's promised me a brake testing brick this year.
Look out for the men in white coats as I think they will be there before Santa. Regards. D4KGP.
 
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