Measuring Rotational Speed and Energy Conservation of a Disc

[chandran]

i have a rotating disc. I have a tachometer and a sensor tape. Where should
i stick the tape to measure the rpm correctly? How tachometer works?


One more question.

a rotating disc has kinetic energy. Why we study energy of a rotating.
Now if i stop the rotating disc according to law of conservation of energy where that lost energy gone?

 

[Doc Al]

Now if i stop the rotating disc according to law of conservation of energy where that lost energy gone?

If you toss a ball in the air and catch it, where does the energy go? Same idea. The kinetic energy of the disk will be transformed to other forms of energy, such as thermal energy.

 

[FredGarvin]

Most things we measure the rotational speed on, we simply put the tape somewhere on ther perifery of the part that is easy for the tachometer to pick up. Since you are measuring rotational speed it doesn't matter where you put it. The result is a frequency that is directly related to angular speed.