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How many seconds for the first 60 ft?


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Hi, I'm new here. My wife and I have a greyhound that we got through the Greyhound Adoption League here in Tucson. Her name is Zippy, we've had her for about 8 years and love her a lot.

I'm impressed at the explosive acceleration these dogs have. I am also a little bit of a car nut and was wondering how a greyhound compares to a fast car in how long it takes to cover the first 60 feet. A fast car could do it in under 2 seconds. How long does it take your average greyhound race dog to cover 60 feet from a standing start?

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Hi and Welcome!  I don't know how acurate this is but I have heard that a grey can reach speeds up to 35 mph in three strides.  Maybe someone else here can help you out more.  I know nothing about cars.   :rasberry

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A car can reach 60 ft. in 2 seconds from a standing start?

 

Somewhere I saw a funny post where someone had worked out the physics of how fast/with what force a greyhound would reach the end of a 16-ft. flexileash, maybe someone can work out something similar for 60 feet.

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Here's the info on Greyhound Physics: The first assumption about acceleration might give a clue.

 

 

1. GH acceleration.  Successful racing Greyhounds must hit a speed of 42 mph and must do so in 6 seconds.

42 mph  =  61.6 ft/sec  = 18.8 m/sec

0 to 42 mph in 6 seconds is therefore an acceleration rate of:

10.3 ft/s^2  =  3.13 m/s^2  (approx. 1/3 rate of gravity)

 

2. A dog on a leash "sees" something an bolts for it. Assuming a dog starts from rest, how far will it go and how fast will it be going by the time a human reacts to the movement?   I assume that it takes 2/5's of a second to become aware of the dog's motion and a further 1/5 of a second to react by tensing you arm.  Total human reaction time is therefore 0.6 sec. Using the standard equations of motion for distance(d) and velocity(v) we see that:

d = 1/2 at^2  = 1.85 ft  =  0.56 meters (distance dog travels in 0.6 sec.)

v = at = 6.18 ft/sec  =  1.88 m/sec = 4.2 mph (speed of dog in 0.6 sec)

 

3. You have a six foot leash.  How long will it take the dog to get to the end of the leash and how fast will it be going when it gets there?

t = sqr(2*d/a) = 1.08 sec.  (NOTE: 0.4 sec AFTER you react to movement)

v = at = 11.1 ft/sec   =  3.38 m/s  =  7.6 mph

4. Your dog weighs 66 lbs. (mass of 30 kg). The dog hits the end of the leash.  How much force does this apply?

First we have to calculate the deceleration of the dog (a').

ASSUME it takes 1/10 of a second to stop dog and leash is not elastic.

Dog goes from 11.1 ft/sec to 0 ft/sec in 0.1 sec.

a' = dv/dt = 111 ft/s^2  = 33.8 m/s^2.

Force applied to leash (and your arm)

F = ma' = (30 kg)*(33.8 m/s^2)  =  1014 Newtons  = 228 lbs.!!!! No wonder you get knocked down!!  Remember, all of this took place in 1.18 seconds.  So there you have it.  These numbers are what is known as an "order of magnitude" calculation commonly referred to as "ballpark" calculations.

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awesome!!  :colgate

 

The only other variable would be that the rate of acceleration is not linier. I am pretty sure he/she would take a lot less time to go from 0-21mph then from 21-42mph. They are pretty torquey have a lower powerband :lol

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Quote from Greyhound Goddess, posted on Oct. 11 2001,09:37,am

Here's the info on Greyhound Physics: The first assumption about acceleration might give a clue.

 

1. GH acceleration.  Successful racing Greyhounds must hit a speed of 42 mph and must do so in 6 seconds.

42 mph  =  61.6 ft/sec  = 18.8 m/sec

0 to 42 mph in 6 seconds is therefore an acceleration rate of:

10.3 ft/s^2  =  3.13 m/s^2  (approx. 1/3 rate of gravity)............

 

 

Thanks for the welcome everybody!

 

Greyhound Goddess: I'm usually pretty good with my math but you lost me right after "The first assumption about acceleration might give a clue"  :0

I see you calculated how long it takes to reach the end of a leash, and how much force you feel when said dog reaches the end of said leash; could you please do some additional calculating to see the amount of time it takes to cover 60 feet from a standing start (not counting reaction time)?

Thanks.

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Bob T, I am a tax lawyer, not an expert in physics!!  :nervous I got this somewhere when we were debating on this board whether to use retractable leashes or not.  

 

Post script - I went ahead and bought the retractable leashes, and one of the first times out (with Luke, of course, the bad boy) ended up on my hiney, in mud,  with my arm just about wrenched out of the socket. What was described in the doggie physics is EXACTLY what happed to me!!

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All toooooooo funny ... especially to some one who hates to balance a check book!

 

Welcome to GreyTalk. I am also in Tucson and work with AGR. Great to see you on line.  

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