And I thought I had anticipated that objection :headbang:
First, I'm just following Feynman, someone for whom I have great respect.
Secondly, in what sense is "a light inextensible string passing over a frictionless pulley" not a "highly idealized academic example"? It, and a "point mass"...
I apologise profusely :mad: as my fingers did not type what my mind was thinking.
I meant an infinite plate of zero thickness and of uniform mass density.
The gravitational force is then uniform throughout the region and there are no tidal forces either parallel or perpendicular to the plate...
May I suggest you start by reading Fictitious force as I think it will greatly assist you in understanding fictitious forces. I gave a few examples in my post above - they may also help your understanding.
If you always do your analyses using an inertial frame of reference you never see...
It does seem to me that a number of posters (I have one, not vanheese71, in mind!) are more keen to demonstrate their depth of knowledge than to put themselves in the shoes of the questioner and answer the question without bringing up minutiae which serve only to confuse and digress.
One gives...
Interesting quibble when one sees the generality of what the OP was asking in a sub-forum entitled Classical Physics and at Basic (High school) level.
Quibbling your quibble, does that apply at a point? Don't tidal forces require an extended region?
No and yes. It is also a matter of semantics and how people decide to describe things.
No because the force a body feels when attracted by a massive body is due to the body's interaction with the curved space time created by the massive body as is described by GR. However, describing it as...
The balloons originally balanced so they each weigh the same.
You then blew into one balloon which pushed more air into it.
When you put it back on the balance you see it is now heavier than the other balloon.
Hence the air you blew into it must have had weight to cause the balloon to be...
While painting the garage door I thought of a possible addition to your lovely experiment.
Ask the students to calculate how much the water in one foot of the tube weighs. And how much the water in 32 feet of the tube weighs.
Attach a spring balance to the top of the tube and record its...
Thank you for that point as you have explained the precise reason for my post.
In general, teachers teach special, simplified cases. The majority of students think they understand it but they understand the special case and not the general principle. Then, when the exam comes, the teacher...
The school explanation only works because the fluid in the bowl and the fluid in the tube are the same. If the fluids are different the school explanation does not work. As so often happens, the school example is a special, simplified case.
The important point at which to equate the pressure...
The manner in which barometers are taught is very misleading.
The important level is the base of the tube where the pressure from the mercury in the entire tube (h + d) must be balanced by the pressure from the atmosphere plus the pressure from the depth d of mercury in the bowl. If they are...
I wonder if that is an evolutionary effect. If we follow the stereotype of the man hunting then when he is tracking an animal as it travels through different lightings (eg from light to shade in a forest) needs to be able to see the same "effective" colour even though the "actual" colour...
I thought I would search NASA (I searched with treadmill) and came across Biomechanics of Treadmill Locomotion on the International Space Station: Does gravity influence running biomechanics? as a starter.
Biomechanics of Treadmill Locomotion on the International Space Station: Does gravity...
This may be just poor use of words but the runner's CoG is not held to the floor.
The whole point is that the runner's CoG goes up and down and, to a first approximation, that defines how much effort they expend.
The straps do not "hold your CoG to the floor". The straps apply a force...
Please remember the original question is "Does running on a treadmill on the Space Station require broadly the same effort as running on earth? ... Let's ignore second order effects" .
When her leg pushes on the treadmill she causes her body's CoG to "rise". That is the analysis where we can...
I completely disagree.
First, I agree that on the ISS your arms and legs have no weight - they are completely weightless.
But I completely disagree that "It requires no effort to lift them" (where lift should be in quotes as there is no up or down on the ISS).
Your leg (and arm) has mass and...
While that is correct if one delves into great detail Newton's Superb Theorem proved that for a solid spherical body in a uniform gravitational field the entire mass can be considered to be located at the CoG and all analyses will be correct.
So, in general, ignoring second order effects, I...
May I pick up several points.
1. You will see that in Post #3 I reasoned that the elastic straps must be pre-tensioned to be equal to the runner's weight on earth. If the runner's CoG rises by, say, a few cm, the restraining force exerted by the elastic strap, which is about 1m long, will be...
Thank you. I can now answer my own question.
If the straps are adjusted so they pull the astronaut towards to treadmill with a force equal to her weight on Earth then effectively it requires the same effort to run on the Space Station as it does to run on earth.
When a runner pushes off with...
The ISS includes a very fancy running machine which astronauts use to maintain fitness. Several astronauts have run Marathons at the same time as the earthly race (London, Boston etc) and, while there have been many press reports of these runs, none has given any indication as to how hard it is...