What happens as soon as you turn a CD also fast? The price is the it shatters. The slow-moving Mo Guys recorded some high speed video showing just just how it breaks.

You are watching: How fast does a dvd spin


What happens as soon as you take expensive equipment and also do silly points with it? Awesome stuff is the correct answer—this is exactly what the slow Mo guy did and here is the complete video. Yes, ns love the slow Mo Guys—who doesn’t. But what i really love is see cool things that no one experienced before. The is exactly what taken place when they offered a high rate camera through a spinning Compact Disc. It turns out the these discs shatter when you turn them also fast—with a high rate camera, you have the right to see the propagation of product failure together the bowl spins.

It’s together a good video, let’s carry out some analysis.

How fast Was the CD Spinning?

They break number of CDs, however let me look at the 2nd CD lock shattered taped at 61,960 frames every second. I tried to use the greater speed video, yet I was obtaining repeating frames—not certain why. The guys claim the crucial spin rate for a CD is 23,000 rpm. Let’s check out if us can get the yes, really spin price for this shattering CD. Yes, ns am going to usage Tracker video clip Analysis—it’s cost-free and awesome (do I need to keep on speak this)?

After loading the video into Tracker, ns can set the range by suspect the diameter the a CD is 12 cm. Next, I can put the origin in the center of the CD and also track some mark as that spins (before exploding). Here is what i get.


From this, I acquire an angular velocity (slope of the angle-vs-time graph) of 3.914 x 10 3 radians/second which is 37,375 rpm. This is rather a bit higher than 23,000 rpm (but of course you know that). Ok, one little issue. Ns am going through the assumption that this video clip reflects all the frames and that each structure is indeed 1/61,960 seconds.

Analysis of paris Stuff

Really, this is like a standard physics question. The goes something prefer this.


A human being swings a ball around in a horizontal one (the view over is from the top). While swinging, the cable breaks. What course does the ball follow after ~ the cable breaks?

The question is frequently in a multiple-choice format, yet you obtain the idea. A common answer is the the sphere will move away from the facility of the circle when the cable breaks.

Let’s look at the CD. What walk a piece of the CD carry out after it breaks free? below is a plot that the piece’s trajectory (x vs. Y).



I know what you are thinking: “oh look, the route of the piece is type of curving.” Well, actually—no. The upright axis is in a much smaller range than the horizontal axis. This data has some time prior to the piece damaged off and also then ~ that, the piece was spinning together it to be flung off. The piece damaged off at almost the exact bottom of the CD and so it largely only had actually a horizontal velocity. Below is a plot of the x-position vs. Time because that that piece (technically, I marked a corner of the piece).



Notice the it isn’t rather a consistent velocity (that would be a straight line in an x-t graph). Instead, this item seems to it is in slowing down (appears—but maybe not actually slowing due to the fact that I am just looking at the corner of a turn piece). Native the quadratic fit, ns can gain the velocity in ~ t = 0 seconds at roughly 453.2 m/s (1014 mph). Is this what it need to be? For an object moving in a circle (like it to be at the start of the motion), the complying with shows the relationship in between the angular velocity, the radius that the circle and the straight speed.


Using one R of 0.12 m and an ω the 3.914 x 10 3 rad/s, I acquire a linear speed that 469.68 m/s. BOOM. Nearly exactly the very same as native the video analysis. Yet what about the acceleration? indigenous the quadratic fit, the CD piece has an acceleration the -2.138 x 10 -5 m/s 2. Why would it have an acceleration favor that? I would guess it’s as result of air resistance. I think over there is something cool here, but I to be going to leaving it together a homework question (see below).

What around the rotation of the item of the CD that flies off? If ns measure the position of two ends of the piece, I have the right to use those to get an angular orientation the the piece. Here is a plot the the angle of that item as a function of time.


This gives it one angular velocity the 6.05 x 10 3 rad/s. Yet why must this piece be spinning in ~ all? I have two guesses to begin with. First, if you clock the method the CD division one finish of the item becomes free before the other end. That way that the rest of the CD is tho pulling ~ above one side of the piece which causes it come spin on release. My 2nd guess has to do with angular momentum. If you think about the piece while the is still associated to the CD, that piece is rotating (it goes from oriented as much as down and ago to up as the CD spins). If the piece has actually angular momentum before the break, it have to still have angular momentum after the break.

Summary and Homework

First, below is a diagram reflecting the course of a item of the CD.



Before the CD breaks, the remainder of the CD exerts a force on the CD piece resulting in it to relocate in a circular path. After the break, this pressure is no much longer there. What carry out objects without forces on lock do? The exactly answer is the they don’t readjust their inert (velocity would be acceptable). Moving in a directly line way the thing has consistent velocity.

But wait! The piece does advice after the break. Yes, i think this is because of air resistance (just a guess).

Now for part homework. There is much to be done.

If a piece damaged of in such a manner that it shot directly up, would you be able to see a adjust in speed because of the gravitational force? If so, might you use this acceleration to examine that the structure rate is correct? If not, why not?

If there is undoubtedly a significant air resistance on the piece of CD, have the right to you detect this force on other pieces too? need to a smaller piece have actually a higher or reduced acceleration due to air resistance? calculation the mass of a item (based ~ above the size) to gain a sphere park figure for the acceleration because of air resistance.

Why walk a broken CD piece spin (or why execute some spin)? try looking at other pieces and also measure their post-break rotate rate. Do other pieces spin the same?

Big project: track all the pieces of the broken CD because that a brief time after ~ the CD breaks. Calculation the massive of every piece based upon the area density of a CD and also the area the a piece. Is kinetic energy conserved (should the be)? Is angular momentum conserved? do a plot of straight speed as a role of beginning distance indigenous the facility of the CD. Must this plot be linear?

I really want to check out the prize to several of these homework questions. If you don’t answer them, ns might.


Rhett Allain is an associate professor that physics in ~ Southeastern Louisiana University. The enjoys teaching and also talking about physics. Occasionally he takes things apart and can't put them back together.

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