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> we should note that even Einstein himself cautioned against believing spacetime was actually curved. [...] I don't want to appeal to authority Another exampl

> we should note that even Einstein himself cautioned against believing spacetime was actually curved. [...] I don't want to appeal to authority Another example that comes to mind is Max Planck believing that light being absorbed in discrete packets of energy was only a neat mathematical hack he came up with. It took Albert Einstein to say "but what if light is discrete packets". And then as you say Einstein having major reservations against the field of quantum physics that he himself spawned. > if you think gravity isn't a force, drop a brick on your toe By that logic the centrifugal force has to be a force. If you don't believe it, just drive a vehicle around a curve, or whirl a rock on a string.

marcosdumay 2y ago
> By that logic the centrifugal force has to be a force. Are you trying to claim it's not?
- ivansavz 2y ago
  Not the OP, but I think I know what wongarsu is referring to. In order to make an object turn, it needs to experience an centripetal acceleration (towards the centre of rotation). This is the force causing objects to change trajectory. If there is another object inside the turning object (like clothes inside a washer, or a person inside a car) they will "feel" like they are being flug out as if a centrifugal force existed, but actually that is just the effect of Newton's first law: the natural tendency of every moving body is to continue to move in a straight line, so when the containing object is changing direction (due to the centripetal force), Newton's first law tends to push you outwards. All of the above is from the static (world) frame of reference. It is also possible to put a coordinate system on the rotating object, in which case something like a centrifugal force will exit, but we kind of created it by choosing an accelerating reference frame, so it's not real. Sometimes called a pseudoforce.
cryptonector 2y ago
"There is no centrifugal force" is often found together with "centrifugal forces appear as a term when using the frame of reference of the object going around", and this implicitly says that some reference frames are more privileged than others which -in a world that accepts the principle of Relativity- is just not acceptable. So of course gravity is a force, and of course centrifugal forces are real. These dogmas serve to do nothing more than to scare away students, and to make the dogmatic seem like geniuses because only they can understand these things.
- tsimionescu 2y ago
  Relativity, classical Galilean relativity, special relativity, and general relativity, all say that all inertial frames of reference are equivalent. Accelerated frames of reference are not equivalent to inertial ones, nor to each other. That is, there is a difference in all of these theories between an observer who is at rest with a train accelerating towards them, and the same observer accelerating towards a train that is at rest. This doesn't mean that you can't do coordinate transforms to look at the world from the point of view of the accelerated observer, and get apparent forces. But different accelerated observers will come up with different apparent forces, while all intertial observers agree on the same forces experienced by any object.

marcosdumay 2y ago

> By that logic the centrifugal force has to be a force. Are you trying to claim it's not?

ivansavz 2y ago
Not the OP, but I think I know what wongarsu is referring to. In order to make an object turn, it needs to experience an centripetal acceleration (towards the centre of rotation). This is the force causing objects to change trajectory. If there is another object inside the turning object (like clothes inside a washer, or a person inside a car) they will "feel" like they are being flug out as if a centrifugal force existed, but actually that is just the effect of Newton's first law: the natural tendency of every moving body is to continue to move in a straight line, so when the containing object is changing direction (due to the centripetal force), Newton's first law tends to push you outwards. All of the above is from the static (world) frame of reference. It is also possible to put a coordinate system on the rotating object, in which case something like a centrifugal force will exit, but we kind of created it by choosing an accelerating reference frame, so it's not real. Sometimes called a pseudoforce.

cryptonector 2y ago

"There is no centrifugal force" is often found together with "centrifugal forces appear as a term when using the frame of reference of the object going around", and this implicitly says that some reference frames are more privileged than others which -in a world that accepts the principle of Relativity- is just not acceptable. So of course gravity is a force, and of course centrifugal forces are real. These dogmas serve to do nothing more than to scare away students, and to make the dogmatic seem like geniuses because only they can understand these things.

tsimionescu 2y ago
Relativity, classical Galilean relativity, special relativity, and general relativity, all say that all inertial frames of reference are equivalent. Accelerated frames of reference are not equivalent to inertial ones, nor to each other. That is, there is a difference in all of these theories between an observer who is at rest with a train accelerating towards them, and the same observer accelerating towards a train that is at rest. This doesn't mean that you can't do coordinate transforms to look at the world from the point of view of the accelerated observer, and get apparent forces. But different accelerated observers will come up with different apparent forces, while all intertial observers agree on the same forces experienced by any object.