Swinging tray -centripetal force -Greek waiter tray // Homemade Science with Bruce Yeany 

thanks Eagle_Eye

Giuseppe Pipia that's sweet

How did she teach you? What did she explain to you that kept you interested?

ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-dNVtMmLlnoE.html

It is indeed due to the "frame rate" that is causing this phenomenon. LED displays don't show all digits at once. It uses a clock to sequentially show each digit from the lowest significant digit(right most) to the most significant (left most). It uses a series of logic gates that determine which segments of the 7-segment display to turn on, then it changes to the next digit as the clock cycles really quickly. So in reality only one digit is ever lit at a time. However due to the speed at which it cycles through the digits, our brain thinks all of them are lit at the same time. This is known as persistence. Cameras have much shorter persistence and so don' get fooled like our brain does. Although rolling shutter would apply, it is not the main reason why the display is messed up. You can see the rolling shutter effect when sometimes a digit and a half is lit at the same time. As i said, only one digit is supposed to be lit at a time. The rolling shutter captured the first digit lit but as the shutter scans, it ends up scanning the second digit causing seemingly due digits to be on at the same time. The camera's shutter speed relative to the refresh rate of the LED display leads to the camera catching the LEDs turning on and off sequentially. This effect is exacerbated when slowing down the video because each frame is played longer thus slowing down the LED display even further, making it much more obvious. You can see this effect with propeller blades. There's a rather popular video where a helicopter's main rotor is not moving due to the rotation of the propeller matching exactly with the camera's shutter speed.

One of the things I love about posting is how additional information is added. I never considered the differential in the distance from the center of rotation for the water column and how it would affect the centripetal force. I follow your solution and the moment I read through this, wondered of how could we explore this further. The 4 foot plastic tubes that are sold for light protectors might be suitable doing a bit more experimenting, but this will need to wait until summer. Thanks for the explanation.

Velocity in circular motion cannot be constant. You are mixing up velocity with speed. Perhaps the speed could be constant, but the velocity has to change if direction changes.

@@carultch Yes that was a typo error. It's speed what remains constant

I should have mentioned, ALWAYS ALWAYS ALWAYS USE PLASTIC, I would never do this with glass. I've dropped one or two at the end but never had a cup fly off, still I wouldn't risk it

They are falling. It's just that they overshoot their target, because they have sufficient tangential speed.

Veritasium made a video on how to do this

I haven't tried it but will take a look

it is a consequence of Newtons 2nd law: F = m * a which tells us, whenever a force acts, there is acceleration (unless that force is counteracted by another force such that the sum of those 2 forces is 0) You can look at the whole situation in a different way also (which turns out to be equivalent) Every object remains moving in a straight line with some speed. We call that combination of direction and how fast an object is moving the "velocity". (speed is just distance gone with respect to time, velocity also considers the direction. Speed is called a "scalar" (just a number), while velocity is called a "vector" (number in which direction). Velocity thus includes speed but is more then that. (But this is just so in the english language which differentiates between speed and velocity. Other languages don't do that. E.g. in german we use the same word for both and in a physics context we always are talking about "Geschwindigkeit" and strictly mean velocity (the vector) unless the direction is not important. In order to change the velocity of an object, you need acceleration. But this includes the direction also! To make a rolling ball change the direction it is rolling, you need to have some acceleration sideways. There are no 2 different words for accelleration to differentiate the vector version (direction is important) to the scalar version (just the number matters). In a physics context, acceleration is always a vector. (direction plus magnitude). So when changing the velocity of a rolling ball, acceleration comes into play (since accelleration is the way to change velocity) but it depends an the direction the accelleration is applied to what happens. To calculate the effect is pretty simple: it is just the vector addition. If the accelleration is in the same direction as the ball is rolling, then the ball simply rolls faster, if the accelleration is perpendicular (not in line with the velocity), it changes the direction and/or the speed the ball is rolling, if the accelleration is opposing the current direction, the speed decreases (we call that breaking). So how do we get some accelleration? Newtons 2nd law tells us: F = m * a, or by turning things around: a = F / m Apply a force and you will get acceleration. How much? Well, if the force gets stronger you will have more accelleration, if the mass gets more you will have less accelleration (a bicycle has less mass then a car, so the same force accellerates a bike more then a car) Also: I am not sure if you have the same misconception I had when learning those things in my first physics class. The centripetal force is not exactly generated by the object swung. It is the force you have to bring up (e.g. with your arms and which gets transmitted through the string) in order to force the object into the circular path. The circling object creates the centrifugal force, but in order to have it circeling you have to create the centripetal force which exactely counteracts the centrifugal force. If the centripetal force goes away, by e.g. letting go the string, there is nothing forcing the object into the circular path any longer. No circular path also means no centrifugal force any longer and from there on the object just continues in a straight line. So from the point of the string: the centrifugal force created by the object is pointing outwards, the centripetal force created by the human or by a central post is pointing inwards. You might eg. want to watch a the sports discipline of "hammer throwing". You can clearly see, that the athlet is leaning backwards a lot. This creates the centrepetal force counteracting the centrifugal force in order to force the hammer into the circular path. lg-swm.de/wp-content/uploads/2016/09/Simon_Lang_Foto_Heike_Geigl_1-1024x580.jpg

You have several misunderstandings aout this. The centrifugal force is not a real force. It is an apparent force due to being in an accelerating environment. Newton's third law isn't really part of the picture for why anything is happening in this situation. If you draw a free body diagram on this system, there is the force of gravity, and the force of tension. At the top of the circle, they both act downward. At the bottom of the circle, tension acts upward while gravity acts downward. They both add up to mass*acceleration, so acceleration is downward at the top of the circle. And greater than Earth's free fall acceleration, because the tension in the strings also contributes.

At the 12 o'clock position, the acceleration of the system is downward, and greater than 1-g. The tension in the string plus the gravity both pull it downward, and add up to the mass*acceleration, which is directed downward. The apparent gravity in the reference frame of the tray is always directed in the opposite direction of the tension, which means that the water feels as if it is pulled outward, the tray feels as if it is pulled outward, and the glass feels as if it is pulled outward. So what force keeps the water in the glass? No force. It is the inertia of the water as it travels along a path that is changing direction. If you were to break the string, the tray would fly tangent to the circle.

I do not get your objections. Please explain!

Given a string of length r, you need to swing it at a speed at the top of the circle where v^2/r is greater than 9.8 m/sec^2, so that the acceleration at the top of the loop is greater than Earth's g-value.

After a while I tried to convince myself it was a plastic beaker

I NEVER use glass, always plastic. I should have made that clear

for the same reason a moderate wind will not move a glass of water on a table when outside. The force generated by friction (glass standing on table) is stronger then the force generated by the air pressing against the glass. Physics tend to look at effects on a one by one basis and ignoring all other effects in experiments designed to show that one effect. But reality is not so simple. All kind of different effects act together at the same time. Take eg. falling objects. At school you learn the math laws on how to describe that. But in reality there is also another force acting: air resistance. As long as the speed of the falling object is not very high, one can ignore air resistance since it doesn't influence the falling object very much (usually much less then what is measurable in a physics class room). But things get different when the speed gets higher. Skydivers do not fall (in the free fall phase) according to those laws. The difference is the air resistence which increases as the skydiver picks up speed. Why does physics not include air resistance into the laws of falling bodies? Because things then get really complicated. Air resistence is dependent on a lot of things and is not an easy thing to compute.

good question, velocity refers to both speed and a direction and in this case the direction is constantly changing but is the rate of rotation changing? I can't tell for sure, I went back and tried it and also watched the video. it feels like it could be, try spinning something yourself and I would be interested in seeing what you think.

For the accelerometer, "down" would always be perpendicular into the plate. The magnitude it senses would increase but thats all. The accelerometer only senses the resultant force you get by adding the centrifugal acceleration to gravity in the form of a vector addition. But so does the plate. Thus for both of them, their local "down" points into the same direction. so now we are left with one question. When you talk about "horizontal acceleration", from which point of view are you talking? From the point of view of the accelerometer, no there is no horizontal component. For it, the force still acts in its own Z-direction (assuming we can take the plane of the plate as the X/Y plane). For an observer outside the situation is different. He sees, that the plate is tilted against the reference of eg the floor. He is able to decompose the force vector into avertical and a non zero horizontal component.

These forces don't make water stick to a spinning ball. In fact, quite the opposite. The apparent centrifugal force is precisely why you think water can't stick to a spinning ball. I assume you are talking about the Earth, because this is a common flat-Earther's talking point. In that case, it is gravity that keeps the water on the Earth, because Earth is a huge astronomical body with 10^23 times as much mass as a typical person, and gravity accumulates with mass. The fact that the Earth rotates, and the apparent centrifugal force due to the rotation, is only a drop in the bucket compared to the strength of the gravitational field. At the equator, the apparent centrfigual force is 0.0334 N/kg (from v^2/R), and the true gravity is 9.81 N/kg (from G*M/R^2), which yields an effective gravity of 9.78 N/kg that you would measure relative to the surface of the Earth. If you are talking about much smaller spheres, like the granite model of Earth in Vancouver BC, that is supported on a fountain's water jet, in that case it is surface tension that keeps water sticking to a spinning ball.

FIRAT BAYDAR, how could he add Turkish subtitles if he doesn't speak Turkish?

Andrei Macaria How do they have their settings, if there is English subtitles, there are Turkish subtitles. thank you for your interest.

FIRAT BAYDAR, I think you are using google translate so I'm having a hard time understanding what you mean, but if I understand correctly, you want the auto-translated version of CC. you can easily do that by enabling the closed captions, then clicking on the settings wheel -> subtitles/CC -> auto-translate and select Turkish. but this is not an accurate translation (because of the auto-translation system limitations mixed with the auto-generated closed captions weaknesses), so the only real option would be that someone who speaks decently both languages to add a manual translation... and that person is surely not Bruce. hope this helps, cheers!

Andrei Macaria sorry. Are you a girl and a man?

Noel Acosta logically i would say the faster he spins it the more force is applied so the 'heavier' the object same as G force training in those rotating arms if you know what I mean I'm not English

There's no fluctuation in the force of gravity. There is a fluctuation in the apparent weight that you would feel if you were riding on this. What you really would be feeling, is the fluctuation in constraint force, that you instinctively assume opposes gravity, which would correspond to either the tension in the string, or the normal force on the cup, depending on which object you care about.

Yes, it is likely to make a lasting impression on a lot of people, as the tray slams into them. Cool demo, though.

that was quick!

Yea 😊😁😁😚❤

When was your day?

Lol, like 17 years ago. I just meant to comment on the kids' shock when they stopped talking and asked "Is that a golf tee?" That was hilarious. Reminds me of my sister's kids.

This is the man we should be listening to. Very good charlie, I am very proud.

this doesnt make sence becaaause if this is true then we'ds fall off the earth when it spins? but we DONT

NEXT!

EXACTLY

Charlie Lyttle ITS FOR A CHURCH GROUP HONEY!

I wish that were true but he died when I was one year old, I posed with a wax figure