[alancalverd (OP)]

It's an everyday observation but never seems to appear in an exam question.

I've just watched my 80 kg neighbor being pulled along by his 10 kg dog on a lead. The dog was clearly in control of their horizontal velocity, from v = 0 in the vicinity of an interesting gate post, up to about 12 m/s in visual range of another dog. The lead was at 45 deg to the horizontal. They were on a level tarmac sidewalk, so the dog had no frictional advantage (claws work better in soft ground, but dog paw pads and leather shoes probably have the same μ value on tarmac).   

Explain.

[varsigma]

It's an everyday observation but never seems to appear in an exam question.

I've just watched my 80 kg neighbor being pulled along by his 10 kg dog on a lead. The dog was clearly in control of their horizontal velocity, from v = 0 in the vicinity of an interesting gate post, up to about 12 m/s in visual range of another dog. The lead was at 45 deg to the horizontal. They were on a level tarmac sidewalk, so the dog had no frictional advantage (claws work better in soft ground, but dog paw pads and leather shoes probably have the same μ value on tarmac).   

Explain.

The dog has the advantage once the man is bent forward and off balance. In order the stop the dog, the man has to haul back with more than one arm, and they have to stop leaning forward.

[vhfpmr]

That reminds me of an occasion when I was helping out at an aunt's dog show. I spotted  a little old lady with three Irish wolfhounds, each one of which must have weighed more than she did. I thought at the time we'll soon see who's boss if they spot a cat.

[paul cotter]

Four legs versus two makes a huge stability gain. Anyway it makes no difference since "ignorance of the law is no defence" ( why is there no smiley face emoji to adorn this?)

[alancalverd (OP)]

link=topic=86512.msg713131#msg713131 date=1695208880]The dog has the advantage once the man is bent forward and off balance. In order the stop the dog, the man has to haul back with more than one arm, and they have to stop leaning forward.[/quote]
But in this case the man was actually leaning backwards and pulljng at 45 deg upwards, so the 10 kg dog was only exerting about 70 N downforce on his pads, and the man had about 815 N downforce on his shoes.

The odd thing is that if you pick the dog up, you can carry it wherever you want. The laws of physics only cease to apply when the dog is in contact with the ground.

[varsigma]

I'll just add an anecdotal amount of evidence about small dogs on leashes, and what happens to humans, including this one, when they let the dog lead them down some stairs. The best option for the human is to let go of the leash.

[alancalverd (OP)]

We had a rewarding year as puppy-walkers for a guide dog. For some reason, "Ice" (what else would you call a classic white lab/golden cross?) disliked the idea of stairs and was distinctly scared of escalators. I took her to the top of the escalator in a local shopping mall and she patiently led me back to the lift - I relented on the third trip. Good news was that she did eventually graduate, clearly enjoyed the work, and retired to a great family.

[Bored chemist]

For a moment, consider moments.

A dog with a connection to the lead that's a foot above the ground has a big torque advantage over a human with a connection near six feet above it.

[Bored chemist]

We had a rewarding year as puppy-walkers for a guide dog. For some reason, "Ice" (what else would you call a classic white lab/golden cross?) disliked the idea of stairs and was distinctly scared of escalators. I took her to the top of the escalator in a local shopping mall and she patiently led me back to the lift - I relented on the third trip. Good news was that she did eventually graduate, clearly enjoyed the work, and retired to a great family.

A guide dog that tried to get a blind human down the escalator would be... less useful...  than one who found the  lift.
I'm delighted to hear that she eventually taught you this, even if it took three goes.

[alancalverd (OP)]

Not all shops and Tube stations have lifts, and even those that do aren't always easy to use - you need to find four different ones, apparently distributed at random,  to get from Kings Cross underground to any main line platform. The essence of training a guide dog is for her to be comfortable wherever and however humans normally go*. Part of the fun of puppy-walking is travelling by bus, plane**, whatever, and visiting pubs. Apart from peeing in the post office (though it did get us to the head of the queue) Ice was brilliant. 

* Except on London Underground, of course, where the escalator signs used to say "dogs must be carried". Fortunately neither guide dogs nor their owners can read the notice, and they both quickly learn to step over the exit comb.   

**Yes, we did the pilot uniform, sunglasses and guide dog shtick. Always a good one.

[Bored chemist]

Not all shops and Tube stations have lifts, and even those that do aren't always easy to use

And yet Ice still had the sense to find one.
Good dog!

[alancalverd (OP)]

Ah, the woke approach to education and training. "Sorry, folks, the captain doesn't like Calais so we'll go to Dover instead."

[varsigma]

For a moment, consider moments.

A dog with a connection to the lead that's a foot above the ground has a big torque advantage over a human with a connection near six feet above it.

Dogs have a keen sense of when they're pulling you off balance; I guess if you don't want them doing it you have to haul them in. A lot of owners have little idea about training a dog to heel properly, dogs, even well trained ones, can sense when they're dragging an inexperienced human around.

Horses, similarly, can tell if the human that just climbed on board knows how to ride or control a horse.

[Bored chemist]

Ah, the woke approach to education and training. "Sorry, folks, the captain doesn't like Calais so we'll go to Dover instead."

Nothing like that actually happened, did it?