Changes In Objects

[herme3]

When you put a music CD in my portable CD player, the CD starts spinning so the player will know if a CD is in there or not. It also reads the index on the CD so it knows how many songs are on the CD. This process takes a few seconds, and when it is done the CD stops spinning until you press the play button.

 

What I find interesting is the number of times the CD rotates during this process. The player performs the same simple instructions every time you put in a CD and close the cover. However, the CD appears to rotate differently each time. To prove this, put a CD player similar to mine on a flat surface, and have the player facing you. Put a CD in, and have the text on the CD facing you so you can read it easily. Now, close the lid and let the player check the CD. When it is done spinning, open the lid and look at the text on the CD. It may be turned sideways, upside-down, or in the same direction as when you first put the CD in.

 

If you take the CD out, and then repeat the process again without changing anything, the text on the CD will probably be pointed in a different direction each time you repeat the process. According to science, wouldn't the properties of either the player or the CD had to have changed for this to happen? How can something different happen each time when the properties of the objects don't change? Please let me know your opinion. Thank you.

[insane_alien]

the cd could just take a little longer to slow down or a little shorter. the motor would be warmer since its ran for a while this could affect the rotation. or it could be simple random effects like the laser took a microsecond longer to start reading. there are too many factors. the batteries would be slightly drained as well which would affect it.

[swansont]

Chaos theory. Sensitivity to initial conditions - you aren't aligning things exactly the same in each trial, so the spin-up is a little different each time. Rotation speed isn't exactly the same. Fluctuations in the system during spin-down. As you repeat the measurements, the temperature has changed, and that has some influence somewhere in the system. And probably several more influences.

[herme3]

I don't think that many things could have changed. The motor wouldn't warm up very much after rotating for only a few seconds. Also, the amount of electricity going into the motor is very precise. I forgot the exact RPM of a CD player, but the CD always turns at that exact speed. If the battery is drained to the point where the motor can't turn at that exact RPM, the player tells you to replace the batteries.

 

I don't understand why the laser would take a different amount of time to read the CD, because the player's programming uses the exact same instructions every time the lid is closed. I guess I can't align the CD exactly each time, but I don't see how the slightest difference in alignment could make the CD rotate a different number of times.

[insane_alien]

if the batteries arwe drained then the acceleration to the set speed takes a bit longer if this happens then the laser has missed a bit of the index when it turns on so it has to wait until the start of the index comes round again. there are loads of other factors and the motor can heat up easily. around 1 degree celsius of difference can affect it noticeably (i done some experiments on electric motors at school and we could notice differences without equipment at this temp difference but it was a crappy motor that could hardly rotate itself.

[5614]

If you place the CD in a way that when it first starts up it misses the index it needs to read it needs to rotate almost a whole circle before it can read it again... It is the effect of lots of little non-indentical things in each experiment which will cause the end result... when the CD player has stopped reading the CD the motor will stop being powered, it will not brake as such, just stop being powered, but the previous momentum of the CD will mean it continues spinning for a bit, in such a situation tiny factors will have a more noticeable effect.