Welcome to the North American Subaru Impreza Owners Club Wednesday August 23, 2017
Home Forums WikiNASIOC Products Store Modifications Upgrade Garage
Go Back   NASIOC > NASIOC General > News & Rumors > Non-Subaru News & Rumors

Welcome to NASIOC - The world's largest online community for Subaru enthusiasts!
Welcome to the NASIOC.com Subaru forum.

You are currently viewing our forum as a guest, which gives you limited access to view most discussions and access our other features. By joining our community, free of charge, you will have access to post topics, communicate privately with other members (PM), respond to polls, upload content and access many other special features. Registration is free, fast and simple, so please join our community today!

If you have any problems with the registration process or your account login, please contact us.
* Registered users of the site do not see these ads. 
Thread Tools Display Modes
Old 08-24-2011, 01:24 PM   #1
Scooby Guru
Member#: 73805
Join Date: Nov 2004
Location: NEPA
2017 911 Turbo
Miami Blue

Default Video: What's Wrong With the "Flintstones" Approach to Braking

Anyone who has ever seen The Flintstones is probably aware of the unique braking mechanism on Fred’s stone age car. I always considered the technique of dragging your feet on the ground to bring your vehicle to a stop a matter of artistic license. Until last week, when this video appeared. It provides us with an excellent real-world example where knowing a little physics might have prevented this Michigan driver with failed brakes from attempting a cross-town drive using “The Flintstone Technique”, and possibly putting himself in the running for this year's Darwin Awards.

Video here

If it isn’t already obvious that this is not a good idea, let’s apply some simple physics to illustrate exactly why. There are a couple of ways to analyze this, but we will use the concepts of Energy and Work. Basically, the kinetic energy (KE = 1/2mv2) that the car possesses before the brakes are applied must be dissipated by the work (W = Fd) done by friction on the car. To come to a stop:

1/2mv2 – Fd = 0

According to the local newspaper, the driver of the defective truck was travelling at speeds up to 40 miles per hour (or about 18 m/s). Under normal circumstances, the braking distance for a vehicle travelling at this speed is about 80 feet (24 meters). We can solve for the braking force required from the equation above assuming a typical mass of about 2100 kilograms for this kind of truck:

F = 1/2(2100 kg)(18m/s)2/24m = 14,200 N or 3200 pounds.

A driver who is not Superman won't be able to exert 3200 pounds of force on the ground. So, assuming normal human strength, let’s calculate how much distance it should take for his truck to slow to a halt. Resting on the ground, an object will exert a force on the ground equal to the weight of the object (W = mg). However, this guy is hanging his feet out the side of the truck, which is going to make it much more difficult to push into the asphalt. Let’s estimate he can push down with a force about a quarter of his weight. If he weighs 200 pounds, this would result in a force of 50 pounds, or 225 N. We also know that the force of friction (F) between his feet and the asphalt depends on the force with which he pushes down (N) and the “coefficient of kinetic friction”(μ) between the soles of his shoes, which we will assume are made of rubber, and the pavement.

F = μN

The μ between rubber and asphalt varies between 0.5 and 0.8. Let's assume a value of 0.7. Therefore, solving for stopping distance, we get:
D = ½(2100kg)(18m/s)2/(0.7)(225N) = 2160 meters, or over 1.3 miles!
The situation might be improved if he exerted his full 200 pounds, or 900 Newtons, of force against the ground. In that case:

D = 1/2(2100kg)(18m/s)2/(0.7)(900N) = 540 meters (about a third of a mile)

However, the amount of torque exerted on his ankles and knees might make that a problematic proposition.

Clearly this driver (and everyone within his radius of influence) got lucky as he rolled through red lights, stop signs and other traffic obstructions in heavy cross traffic. With a little knowledge of basic physics, though, he could have avoided an appointment with the Michigan court system, possible jail time, and public ridicule. Remember, friends don’t let friends drive without brakes.

Finally, in case you’re interested, automobile brakes work so well due to the wondrous principles of hydraulics. Because the pressure is the same everywhere within a confined fluid (that's Pascal’s principle), applying a small force (F = PA) to a small area at one end of the system (the brake lines behind the brake pedal) results in a much larger force being applied at the other end, where the fluid expands to a significantly greater area against the brake pads.

* Registered users of the site do not see these ads.
AVANTI R5 is offline   Reply With Quote
Sponsored Links
* Registered users of the site do not see these ads.
Old 08-24-2011, 02:21 PM   #2
Scooby Specialist
Member#: 158043
Join Date: Aug 2007
Chapter/Region: RMIC
Location: SLC
2013 Wrx Hatch


What a moron
Not-EWRX is offline   Reply With Quote
Old 08-24-2011, 04:53 PM   #3
Scooby Specialist
Member#: 171611
Join Date: Feb 2008
Chapter/Region: BAIC
Location: Silicon Valley
2014 FiST


If only Brembo made some.....
Lboogie is offline   Reply With Quote
Old 08-24-2011, 06:27 PM   #4
Optimus Prime
Scooby Specialist
Member#: 69847
Join Date: Sep 2004
Location: Cybertron
2017 AMG C43


Optimus Prime is offline   Reply With Quote
Old 08-24-2011, 11:46 PM   #5
Scooby Specialist
Member#: 88099
Join Date: May 2005
Chapter/Region: NESIC
Location: Freeport, ME/Prov, RI
2004 Audi S4
2003 Suzuki SV1000S


lord i hate physics...and this guy is just a retard
doylfish is offline   Reply With Quote
Old 08-25-2011, 11:29 AM   #6
Scooby Specialist
Member#: 169223
Join Date: Jan 2008

maybe he was just improvising because he just put brand new racing brakes on but they have no grip whatsoever when cold... and no the guy does not track his car but like a lot of young car owners out there, he wanted race pads because they are wicked kewl.
JuggernautTCW is offline   Reply With Quote
Old 08-26-2011, 12:11 AM   #7
Scooby Specialist
Member#: 115480
Join Date: May 2006
Location: St. Pete, FL

I'm not Mr. Wizard or anything, but the article also forgot to mention you can't stop a truck going 40mph with your feet because friction will be burning your damn shoes/feet off. Y'know... in addition to all the other reasons it's stupid.
Skunkers is offline   Reply With Quote
Old 08-26-2011, 04:29 AM   #8
Scooby Newbie
Member#: 292189
Join Date: Aug 2011

Originally Posted by JuggernautTCW View Post
maybe he was just improvising because he just put brand new racing brakes on but they have no grip whatsoever when cold... and no the guy does not track his car but like a lot of young car owners out there, he wanted race pads because they are wicked kewl.
LOL that happens a lot too.
TheWatcher is offline   Reply With Quote

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
I wanted to know what's wrong with the world today... OriginalSin Off-Topic 17 01-14-2009 03:14 PM
('93-'01) What's wrong with the message board?? KavMan Impreza Forum 5 04-26-2001 02:15 PM
What's wrong with the calculation? tonytiger Normally Aspirated Powertrain 10 04-25-2001 09:43 AM
What's wrong with the Toronto subaru board? Robin2 Canada Region Forum 4 02-14-2001 08:45 PM
Imprezer- What's wrong with the EJ20? MikeYOX Technical Forum Archive 83 08-17-2000 07:46 PM

All times are GMT -4. The time now is 11:03 AM.

Powered by vBulletin® Version 3.7.0
Copyright ©2000 - 2017, Jelsoft Enterprises Ltd.
Powered by Searchlight © 2017 Axivo Inc.
Copyright ©1999 - 2017, North American Subaru Impreza Owners Club, Inc.