Five Day. It has been a difficult week. Much discomfort in the joints. And today portends to be a nasty one for weather. And then into the abyss that is week out. So my morale and mood have not been good.
Hence it was with a somewhat negative view that I noted an article [Link] this week. It is about some research (?????????) done by French “scientists” on “rolling luggage”. The thing with “rolling luggage” is that everyone’s time is golden so long as it is one’s own (?) time and not someone else’s which is stercus. So no one wants to wait for checked luggage and insists on traveling with a miniature suitcase with a long handle and a pair of wheels either mounted on an axle or incorporated into the structure of the suitcase. And they drag, not roll, these suitcases through the aeroports and onto airliners where half of the suitcases end up checked baggage anyway because the room in the bins is quickly exhausted.
From a physics standpoint what is important here is that the wheels are of fixed orientation and the suitcase is under continual force. If the wheels are on an axle, they are fixed but the axle can rotate. As these are pulled through the aeroport the suitcase tends to wobble, sometimes violently, and even tip over like a ship in high seas. Sadly, the suitcases that do tip do not sink, they just cause several other travelers to trip over them and cause a traffic jam and much ill will all about.
That latter is not physics, thankfully.
Back when I was a bairn, I had a couple of toy cars. These cars were made in Japan of hammered and painted tin and they had four rubber or plastic tires, in pairs mounted on metal axles. (Plastic was expensive in those days.) And when you would push these cars as hard as you could, they would run straight for a while (if they didn’t flip immediately) then veer off and even flip over. By the time my younger brother came along and played with toy cars, the body was now plastic but the behavior was the same.
This is why when I saw the article I was immediately cynical and thought this was nothing but self-promotion. After all, the French, as a people, are known for their arrogance. Most places you go, if you sincerely try to speak the language, you are warmly welcomed. In France, if you try to speak French, the French will try to kill you.
Basically, the suitcase is an extended version of the toy car. Since the wheels are fixed in orientation, and, if mounted on an axle, constrained to rotate together. and under continual force, every little variation in the rolling surface – floor, for the bogs – causes a perturbation. In addition, and this is the real biggie, the direction of the force (pull) and the direction of the wheel’s rotation is not the same. So while the wheel is turning, it is also being dragged a bit to the side. If the wheels are mounted on an axle, this dragging causes one side of the suitcase to dig in and stall, at least momentarily. And if you pull the suitcase fast enough, the bumps and drags interfere constructively and you get a Tacoma Narrows bridge event. (Although that’s not really why the bridge collapsed, of course.)
Now why is this article self-promoting? Because every physicist who has traveled since the introduction of “rolling luggage”, has experienced this either directly or by observation and figured out what was going on. And most of us then returned to checked baggage. So this stuff isn’t new. It’s not as bad as going out to the Eiffel Tower and repeating Galileo’s Tower of Pisa experiment – and bragging about as new – but it’s close.
Incidentally, this physics is also close to the reason why Alibam Pickup Truck aimers aren’t competent drivers: the trucks themselves are impossible to steer like a motorcar and the state in its warped politics is unwilling to force pickup drivers to take training in the interest of the safety of the citizenry. Which is why Alibam is a third world state, a toy car state. Absent of understanding of basic physics and absent of any regard for the citizenry.
Much like the contemporary bog traveler.