Wheel momentum Walter Lewin

Battery Electric Vehicles
14 Feb 201103:13
32 Likes 10 Comments

TLDRIn this intriguing demonstration, a wheel is attached to a rope and spun before being released. Initially, the wheel precesses slowly, but when its spin direction is altered, the precession frequency changes dramatically. Adding weight to the wheel's rim increases the precession speed, illustrating the complex relationship between angular momentum, torque, and the moment of inertia. The experiment challenges intuitive expectations and highlights the principles of physics at play.

  • πŸŒ€ A wheel attached to a rope is used in a demonstration, initially showing its tendency to 'clunk' when released.
  • πŸ’« Spinning the wheel before releasing it changes its behavior, causing it to move differently than when not spinning.
  • ⏱️ The spinning wheel, when released, precesses in a clockwise direction when viewed from below.
  • πŸ”„ The wheel's direction of rotation can be altered, affecting how it precesses around the rope.
  • πŸ“ˆ The angular momentum and spin angular momentum are influenced by the applied torque.
  • πŸ”§ The torque is visualized as the spinning momentum chasing the direction of the applied torque.
  • πŸ€” The experiment demonstrates that the physical phenomena involved are not intuitive.
  • πŸ“Š Adding weight (two kilograms) to the system increases the precession frequency instantly.
  • πŸ”© The moment of inertia is not changed by adding mass to the spinning wheel, which affects the torque experienced.
  • πŸ”„ The experiment shows the complex relationship between torque, angular momentum, and the precession frequency.
  • 🧠 Understanding these concepts requires careful observation and analysis, highlighting the importance of experimental physics.
Q & A
  • What happens when the wheel is attached to the rope and released?

    -The wheel will rotate and eventually hit the ground, causing a 'clunk' sound.

  • What is the effect of spinning the wheel before releasing it?

    -The spinning wheel will exhibit a precession motion, changing its orientation due to the conservation of angular momentum.

  • Why does the wheel's precession direction change when the spin direction is altered?

    -The change in precession direction is due to the change in the direction of the angular momentum, which is influenced by the applied torque.

  • What is the significance of the torque in the experiment?

    -The torque is responsible for changing the direction of the angular momentum, causing the wheel to precess in a different direction.

  • How does the experiment demonstrate the conservation of angular momentum?

    -The conservation of angular momentum is shown by the wheel's continued rotation and the change in its precession direction when spun in different ways.

  • What happens when a two-kilogram weight is attached to the spinning wheel?

    -The precession frequency increases instantaneously due to the additional mass altering the wheel's moment of inertia.

  • Why doesn't the moment of inertia change when the two-kilogram weight is added?

    -The moment of inertia does not change because the weight is added to the end of the wheel, which does not affect the distribution of mass around the wheel's axis of rotation.

  • What is the relationship between the torque and the spinning momentum in the experiment?

    -The spinning momentum (angular momentum) is the torque in motion; the wheel's spinning momentum is what the torque is acting upon and chasing.

  • How does the script demonstrate that none of the physical concepts involved are intuitive?

    -The unexpected behavior of the wheel, such as the change in precession direction and frequency with added mass, shows that these concepts cannot be easily predicted without understanding the underlying physics.

  • What is the role of the music in the script?

    -The music serves as a timing element, indicating the duration of the wheel's rotation and the instant when the additional weight is added.

  • How does the script illustrate the concept of precession?

    -The script illustrates precession through the wheel's motion after being spun and released, showing how it moves in a direction different from the axis of rotation due to the applied torque.

🎒 Spinning Wheel Experiment

The paragraph describes a physics experiment involving a string rope with a wheel attached to it. Initially, the wheel is at rest and when released, it makes a clunk sound. The experimenter then spins the wheel before releasing it, causing it to rotate and precess. The direction of rotation and the resulting precession are observed, with the experiment demonstrating the relationship between angular momentum, spin, and torque. The experimenter further alters the system by adding weight (two kilograms) to the end of the rope, which results in an instantaneous increase in the precession frequency. The explanation emphasizes the non-intuitive nature of the physical principles at play.

In the context of the video, a 'string' refers to a flexible cord or rope used to attach and suspend objects. It is fundamental to the experiment being described, where a wheel is attached to the string and spun around before being released. This setup is crucial for demonstrating the principles of angular momentum and precession.
The 'wheel' is a circular object that is a central component in the experiment. It is attached to the string and spun, which then allows for the observation of physical phenomena such as angular momentum and precession. The wheel's movement and orientation are critical in illustrating the concepts discussed in the video.
πŸ’‘angular momentum
Angular momentum is a measure of the rotational motion of an object. In the video, it is a key concept that explains why the spinning wheel behaves in certain ways when released, such as its direction of rotation and the effect of external forces like torque. The conservation of angular momentum is a fundamental principle in physics that is demonstrated through the experiment.
Torque is the rotational equivalent of force and causes an object to rotate around an axis. In the video, torque is applied to the spinning wheel, which results in changes to its angular momentum and precession frequency. The concept is crucial for understanding how the wheel responds to external influences and how it precesses.
Precession is the change in the orientation of an object's rotational axis due to external forces, such as torque. In the video, the precession of the spinning wheel is observed and manipulated to demonstrate the principles of angular momentum and torque. The change in precession frequency is used to illustrate these concepts.
In the context of the video, 'spin' refers to the rotation of the wheel around its axis before it is released. The act of spinning the wheel is essential for setting up the conditions to observe the effects of angular momentum, torque, and precession.
πŸ’‘direction of rotation
The 'direction of rotation' indicates the way in which an object is spinning, either clockwise or counterclockwise. In the video, the direction of the wheel's rotation is important for understanding how it responds to torque and how its precession direction changes.
The 'experiment' refers to the scientific test or procedure described in the video, where a wheel is spun and released to observe its behavior. The experiment is designed to demonstrate principles of physics, such as angular momentum, torque, and precession.
πŸ’‘moment of inertia
The 'moment of inertia' is a measure of an object's resistance to changes in its rotation. It depends on the mass of the object and how that mass is distributed relative to the axis of rotation. In the video, the moment of inertia is relevant when discussing how adding mass to the spinning wheel affects its precession frequency.
The term 'intuitive' refers to something that is easily understood or seems obvious without much thought or analysis. In the video, the narrator emphasizes that the behavior of the spinning wheel and the principles of angular momentum, torque, and precession are not intuitive, meaning they may not be immediately obvious or easy to understand without a deeper knowledge of physics.

Attaching a wheel to a rope and releasing it results in a 'clunk' sound, indicating a clear reaction.

Spinning the wheel before releasing it changes the outcome of the experiment.

The wheel's position changes after spinning, indicating a shift in momentum.

The spinning wheel demonstrates the concept of angular momentum when released.

Changing the direction of the wheel's rotation alters the precession direction.

The experiment visually illustrates the relationship between spin angular momentum and torque.

The torque is shown to chase the spin angular momentum.

The experiment is repeated with an additional weight (two kilograms) attached to the spinning wheel.

An instantaneous increase in precession frequency is observed with the added weight.

The moment of inertia is mentioned as a factor that includes mass (m) in its calculation.

The added object does not change the moment of inertia of the spinning wheel.

The experiment demonstrates non-intuitive aspects of angular momentum and torque.

The spinning wheel serves as a model to understand complex physical concepts.

The experiment showcases the dynamic interaction between torque and angular momentum.

The addition of weight to the spinning wheel provides a practical example of how torque can affect motion.

The experiment visually confirms theoretical predictions about angular momentum and torque.

The wheel's precession frequency is directly influenced by the applied torque.

The experiment is a practical demonstration of the principles of classical mechanics.

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