Measuring Rotational Speed and Energy Conservation of a Disc

• chandran
In summary, the conversation discusses the use of a rotating disc, a tachometer, and a sensor tape to measure RPM. It is suggested to place the tape on the periphery of the rotating part for the tachometer to pick up the frequency. The conversation also touches on the concept of energy and the transformation of kinetic energy into other forms of energy, similar to how the energy of a tossed ball is transformed upon being caught.
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?

chandran said:
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.

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.

1. What is rotational speed and how is it measured?

Rotational speed is the measure of how quickly an object rotates around an axis. It is typically measured in revolutions per minute (RPM) or radians per second (rad/s). To measure rotational speed, we can use a tachometer, which measures the number of revolutions per minute, or a stroboscope, which uses flashing lights to determine the speed at which an object is rotating.

2. How is the energy conservation of a disc related to its rotational speed?

The energy conservation of a disc is related to its rotational speed through the principle of conservation of angular momentum. This principle states that the total angular momentum of a system remains constant unless an external torque is applied. Therefore, as the rotational speed of a disc increases, its angular momentum also increases, and vice versa.

3. Can the rotational speed of a disc be changed without applying external torque?

Yes, the rotational speed of a disc can be changed without applying external torque through the principle of conservation of angular momentum. For example, if a disc is spinning and we extend our arms out, the rotational speed of the disc will decrease due to the increase in its moment of inertia, which is the resistance to change in rotational motion.

4. How does the mass and distribution of mass affect the rotational speed of a disc?

The mass and distribution of mass can affect the rotational speed of a disc through its moment of inertia. Objects with a greater mass or mass distributed further from the axis of rotation will have a larger moment of inertia, making it more difficult to change its rotational speed. Therefore, a disc with a larger mass or mass concentrated further from the center will have a lower rotational speed compared to a disc with a smaller mass or mass distributed closer to the center.

5. How do we calculate the rotational energy of a disc?

The rotational energy of a disc can be calculated using the formula E = 1/2 * I * ω^2, where E is the rotational energy in joules, I is the moment of inertia in kilograms per meter squared, and ω is the angular velocity in radians per second. This formula takes into account the mass and distribution of mass of the disc, as well as its rotational speed, to determine its total rotational energy.

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