At 13:26 I suggest an explanation for the curved path observed by the inertial observer. This is part of the answer. I didn't mention that kinetic friction is not zero when the bottle top is sliding, and that'll also have an impact on the path the bottle top followed. If you can think of a better explanation for the curved path (not a straight path) of the bottle top when it slips from the record, let me know in the comments!
The curved path is definitely due to friction. The cap is still dragged along by the record even when sliding off. Without friction, the cap would follow a straight path from the moment it is released. The conservation of angular momentum has nothing to do with it. That only affects the rotation of the cap itself. While flying off (in a straight line), the cap keeps rotating around its own axis.
By the way, for the plumb in car measurement, it would have been more accurate to measure the angle of the line with the lamppost outside. The car (and therefore the camera image) is tilted to the left because of the centrifugal force as well.
Fascinating and superbly done sir. Love the combination of real world expermiments and theory to solve problems such is the beauty of the study of physics. (You were and are my favorite teacher)
Keith, I believe the curve described by the bluetack balls as they detach from the record is called an involute of the circle, at least in the friction-less case. As the static friction of the balls would be far higher than the sliding or rolling friction I'd say that the friction-less approximation would be a good approximation to the motion you see. For a nice physical explanation of the curve that I learned about. Wrap a few turns of string around a cylinder, or the outside of your record player. Hold the string end with your thumb and finger (which will represent the mass) under slight constant tension. For the inertial frame of reference start with your "mass" on the surface of the cylinder. Gradually rotate the cylinder and the string will unwind at a tangent to the original attachment point. Now, for the non-inertial frame, start in the same way, with the your fingers holding the string end at the surface of the cylinder. Now unwind the string again, but this time keeping the cylinder stationary. You can see that the "mass" leaves the surface of the cylinder perpendicularly now and as you unwind further describes a circular spiral called the involute. I like this string description because you can see how in the inertial case the "mass" actually leaves the cylinder at a tangent and travels at a constant speed exactly as expected from Newtons first law. However, you can also see how in the non-inertial case the mass seems to fly off perpendicular to the cylinder in the direction of the centrifugal force. Two quite different descriptions of the same unwinding action simply by changing your perspective from rotating cylinder to stationary cylinder.
Come on Keith that record was quite nice, brought back memories of primary school in the 70s...Surely you could've found an old Rolf Harris record or Orville " I wish I could fly" etc, now that would have been more apt!😅
My new mission is to find the worst record I can to scratch up 🤣 Oh, no, actually, that feels somehow wrong. Like burning books. Destroying art feels immoral 😬
I'm more upset about the fact that you're using one of those Crossley record players. I bought one as well and couldn't have been more disappointed with the audio quality, even when it's connected to a good set of speakers.
I've never understood the point of looking at all of this. It's simple. Centripetal force is the force that pulls inward on the object rotating around the center. Centrifugal is the *exact opposite* force that wants to pull it outward. The rest of this is irrelevant unless you're trying to do other things like... 1000 yards away.. where you're not looking at it from the "toward-away from center" reference frame.
![Lp. Сердце Вселенной #60 РОЖДЕНИЕ ЛОЛОЛОШКИ [Финал] • Майнкрафт](http://i.ytimg.com/vi/YoR0pAV9FVQ/mqdefault.jpg)
At 13:26 I suggest an explanation for the curved path observed by the inertial observer. This is part of the answer. I didn't mention that kinetic friction is not zero when the bottle top is sliding, and that'll also have an impact on the path the bottle top followed. If you can think of a better explanation for the curved path (not a straight path) of the bottle top when it slips from the record, let me know in the comments!
The curved path is definitely due to friction. The cap is still dragged along by the record even when sliding off. Without friction, the cap would follow a straight path from the moment it is released.
The conservation of angular momentum has nothing to do with it. That only affects the rotation of the cap itself. While flying off (in a straight line), the cap keeps rotating around its own axis.
By the way, for the plumb in car measurement, it would have been more accurate to measure the angle of the line with the lamppost outside. The car (and therefore the camera image) is tilted to the left because of the centrifugal force as well.
"well that's enough of that"
Way ahead of ya boss. I don't think I'd have even dropped the needle on it.
Fascinating and superbly done sir. Love the combination of real world expermiments and theory to solve problems such is the beauty of the study of physics. (You were and are my favorite teacher)
Keith, I believe the curve described by the bluetack balls as they detach from the record is called an involute of the circle, at least in the friction-less case. As the static friction of the balls would be far higher than the sliding or rolling friction I'd say that the friction-less approximation would be a good approximation to the motion you see.
For a nice physical explanation of the curve that I learned about. Wrap a few turns of string around a cylinder, or the outside of your record player. Hold the string end with your thumb and finger (which will represent the mass) under slight constant tension. For the inertial frame of reference start with your "mass" on the surface of the cylinder. Gradually rotate the cylinder and the string will unwind at a tangent to the original attachment point. Now, for the non-inertial frame, start in the same way, with the your fingers holding the string end at the surface of the cylinder. Now unwind the string again, but this time keeping the cylinder stationary. You can see that the "mass" leaves the surface of the cylinder perpendicularly now and as you unwind further describes a circular spiral called the involute.
I like this string description because you can see how in the inertial case the "mass" actually leaves the cylinder at a tangent and travels at a constant speed exactly as expected from Newtons first law. However, you can also see how in the non-inertial case the mass seems to fly off perpendicular to the cylinder in the direction of the centrifugal force. Two quite different descriptions of the same unwinding action simply by changing your perspective from rotating cylinder to stationary cylinder.
Come on Keith that record was quite nice, brought back memories of primary school in the 70s...Surely you could've found an old Rolf Harris record or Orville " I wish I could fly" etc, now that would have been more apt!😅
My new mission is to find the worst record I can to scratch up 🤣
Oh, no, actually, that feels somehow wrong. Like burning books. Destroying art feels immoral 😬
You remind me very much if Jonny Ball and Think of a Number but for physics.
I loved Johnny Ball! What a compliment 😁 thank you
THANK U SO MUCH KEITH🙏🙏🙏
I'm more upset about the fact that you're using one of those Crossley record players. I bought one as well and couldn't have been more disappointed with the audio quality, even when it's connected to a good set of speakers.
Aaaand now I see why you got the cheapest one available. Maybe I'll see if I can come up with any other uses for a terrible record player.
🤣
If centrifugal force doesn't exist
Them what does a centrifuge do, I wonder?
I've never understood the point of looking at all of this. It's simple. Centripetal force is the force that pulls inward on the object rotating around the center. Centrifugal is the *exact opposite* force that wants to pull it outward.
The rest of this is irrelevant unless you're trying to do other things like... 1000 yards away.. where you're not looking at it from the "toward-away from center" reference frame.