The discussion centers on the perceived dishonesty in physics demonstrations of centripetal force, particularly regarding how these demonstrations convey the concept of an "inward pull" on objects in circular motion. Participants critique specific examples, such as a candle flame on a spinning turntable and a cork in water, questioning the accuracy of the explanations provided in these demonstrations.
Participants express a range of opinions, with no consensus on the validity of the demonstrations or the nature of the forces involved. Disagreement persists regarding the interpretation of centripetal force and the explanations provided in the demonstrations.
Participants highlight limitations in the explanations of the demonstrations, including potential misquotes and the need for clearer articulation of the physics involved. There is also mention of the dependence on reference frames when discussing forces in rotating systems.
Borek said:Think about it this way: if there were no inward force, there would be no no circular motion.
If we observe an object moving in circles, something makes it going in circles. Without this "something" the object would move straight ahead. That's the Newton's first law. This "something" is an inward force. What is its origin, how it is applied - that's another thing. But just by seeing how the object behaves, we know that the force must be there.
Nugatory said:No torque if you're rotating at a constant angular velocity.
The spokes are fighting the outwards-stretching tendency of the rim, preventing the rim from stretching even further.
Yes there is. All of these scenarios are the same, you just have to work harder to find it in some cases.d4rr3n said:Yes I do recognize that and that is part of the problem because physicists only talk about an inward force and a tangential force they don't talk about the outward force which is what I find confusing. If you look at the tank of water there is no inwards force on the water..
There is no "at most": the force of the walls pushing in on the water is the force we are talking about! If that forcer were not present, the water would splatter around the room!...if there was it would accumulate in the center of the tank but the opposite occurs. At most you can only talk about the "reactive" inward force of the tank walls resisting the outward force of the water.
Sorry, I wasn't clear: I meant a yoyo at the end of its string, being twirled around your finger. A trick known as "around the world".The yoyo is actually climbing/descending a plain, ie it is the string applying torque on the center of the yoyo that makes it spin
Neither: all force pairs arise simultaneously.d4rr3n said:You can only talk about the spokes fighting the outwards stretching force as a secondary reactive force...btw what is the name of that outward stretching force :) which comes first?
Bandersnatch said:I agree with others. You should draw a free body diagram. Maybe then you'd stop thinking there is a tangential force, among other things.
Best would be to draw two: one in the rotating the other in non-rotating frame, as you keep on mixing the two.
Those two forces are not directly associated. The force that starts the linear/tangential motion is not at issue in any of these scenarios.d4rr3n said:If you put a rocket on a tether so it cannot fly in one direction but instead is forced to move in a circular path (we have all seen these fireworks right) which force is more primary the tether resisting the straight line motion of the rocket or the force provided by the propulsion. Which force is primary and which one is reactive?
russ_watters said:Those two forces are not directly associated. The force that starts the linear/tangential motion is not at issue in any of these scenarios.
d4rr3n said:I don't have difficulty in seeing the centripetal force in the case of an orbiting satellite that's why I said Vs a wagon wheel. Explain to me instead why the spokes of the wheel are in tension and not compression.
d4rr3n said:Ok I'm going to say the tangential force is the primary and these inward/outward force are only reactive secondary forces.
d4rr3n said:Ok I'm going to say the tangential force is the primary and these inward/outward force are only reactive secondary forces.
No. In constant speed motion, the tangential force is zero.d4rr3n said:Ok I'm going to say the tangential force is the primary and these inward/outward force are only reactive secondary forces.