Are solid objects really “solid”?

AlphaPhoenix

28 Jan 202221:28

EducationalLearning

32 Likes 10 Comments

TLDRThe video script explores the concept of how force is transmitted through a solid object, using a steel bar as an example. It challenges the common physics models and approximations, such as the rigid body assumption and the speed of light limitation, by conducting an experiment to measure the delay in force transmission along the bar. The conclusion is that the speed of sound in the material, specifically the extensional speed, best explains the observed delay, offering insights into the atomic structure and behavior of solids.

Takeaways

🌟 The concept of a solid object's movement through space is not instantaneous, even when it appears to be a single unit.
🚀 When scaling up a solid object, like a steel bar, to an extreme length, the time it takes for one end to move after another is pushed becomes significant.
💡 The speed of light is the ultimate speed limit, and even the movement of a solid object cannot exceed this speed.
🎵 The experiment conducted in the script demonstrates that the delay in the movement of the bar is not zero, indicating that it's not an ideal rigid body.
📏 The delay measured in the experiment was 180 microseconds, which aligns with the speed of sound in the material, rather than the speed of light or other factors.
🔍 The atomic structure of steel plays a crucial role in understanding how force and motion are transmitted through the material.
🌐 The speed of sound in a material is well-studied and can be used to predict the delay in the movement of an object made of that material.
🔧 The model of atoms connected by springs is a useful approximation for understanding elastic deformation in materials.
🎥 The experiment showed that the speed of transmission of motion through the steel bar is proportional to the bar's length, confirming the one-dimensional transmission of sound.
📉 The speed of sound in a thin bar is referred to as the extensional speed, which differs from the longitudinal speed in a three-dimensional object.
💭 The experiment and its results highlight the importance of using appropriate physics models and approximations to understand and predict the behavior of objects in the real world.

Q & A

What is the main topic of the transcript?
-The main topic of the transcript is the exploration of how force and motion propagate through a solid object, specifically a steel bar, and the various physics models that can be used to approximate and understand this phenomenon.
How does the speaker introduce the concept of the steel bar experiment?
-The speaker introduces the steel bar experiment by starting with a simple, everyday example of pushing on a solid steel bar and observing the immediate movement at the other end. He then scales up the scenario to a hypothetical 300,000 km long bar to discuss the propagation of force in a more extreme context.
What are the different models the speaker discusses to explain the propagation of force in the steel bar?
-The speaker discusses several models to explain the propagation of force, including the quantum mechanical wave function for every subatomic particle, the rigid body approximation with Newton's laws of motion, and the spring model representing the atomic structure and behavior of materials like steel.
What is the role of the speed of light in this discussion?
-The speed of light is brought up to highlight the theoretical limit on how fast information or force can travel. It is used to challenge the idea of instantaneous force propagation in an object, as per relativity, which states that nothing can travel faster than the speed of light.
How does the speaker address the limitations of the rigid body approximation?
-The speaker acknowledges that the rigid body approximation, which assumes the steel bar moves as a single unit, is an oversimplification. It does not account for the actual atomic structure and the time it takes for the force to propagate through the material, which contradicts the prediction of instantaneous movement in this model.
What is the experiment the speaker conducts to measure the delay in force propagation?
-The speaker conducts an experiment where he pushes on one end of a steel bar and uses a force sensor and a hammer with a circuit at the other end to measure the delay in force propagation. He measures the time it takes for the bar to move and exert force on the sensor at the far end.
What is the result of the speaker's experiment?
-The result of the experiment shows that there is a delay in the force propagation, which is measured to be approximately 180 microseconds. This contradicts the rigid body approximation and supports the idea that the speed of sound in the material is the relevant factor for the delay.
How does the atomic structure of steel relate to the experiment's findings?
-The atomic structure of steel, with its body-centered cubic arrangement of iron atoms and the behavior of electrons acting like springs, helps explain the delay in force propagation. The speaker uses this model to predict that the speed of sound in the steel bar is the key factor in the delay observed in the experiment.
What is the significance of the Poisson ratio in the context of the speed of sound in materials?
-The Poisson ratio, which describes how a material deforms under compression, is significant because it affects the speed of sound in the material. However, for thin bars like the ones used in the experiment, the Poisson ratio has less impact as the sound wave transmission is effectively one-dimensional.
What is the term for the type of sound speed observed in the steel bars in the experiment?
-The type of sound speed observed in the steel bars during the experiment is called the extensional speed of sound. This is different from the longitudinal speed of sound, which would apply to a three-dimensional object like a large cube of steel.
How does the speaker's approach to the experiment reflect the nature of physics?
-The speaker's approach to the experiment reflects the nature of physics as a field that relies on approximations and models to understand complex phenomena. It shows that while these models can provide useful insights, they also have limitations and need to be adapted based on the specific situation and available data.

Outlines

00:00

🌐 Introduction to the Solid Bar Experiment

The video script begins with an introduction to a thought experiment involving a solid object, specifically a bar of steel. The bar, initially described as being 5-8 thick and three feet long, is pushed on one end to demonstrate that the other end moves as well. The experiment then scales up the bar to an enormous size of 300,000 kilometers, or one light second, to explore the physics of force transmission through a solid object. The discussion introduces various possibilities for the delay in the movement of the bar's end, including the speed of light, the speed of sound in the metal, and the material properties of the steel. The segment also touches on the complexity of modeling such a scenario using quantum mechanics and the limitations of our current understanding of physics.

05:02

📏 Rigid Body Approximation and Newton's Laws

The second paragraph delves into the concept of the rigid body approximation and Newton's laws of motion as a simpler way to model the behavior of the steel bar. It explains how this approximation averages out the complexities of quantum mechanics and allows for easy prediction of the bar's movement when pushed. However, the paragraph also highlights the limitations of this model when considering other physical laws, like relativity, which state that nothing can move faster than the speed of light. The paragraph then describes an actual experiment conducted to measure the delay in force transmission through a 91-centimeter steel bar, comparing the predictions to the observed results.

10:03

🔩 The Atomic Structure and Elastic Deformation

This paragraph focuses on the atomic structure of steel and how it relates to the transmission of force through the material. It explains that steel is composed of iron atoms in a body-centered cubic structure, with electrons acting as the glue holding the structure together. The paragraph describes the model of elastic deformation, where atoms are connected by springs, and a compressive wave (or sound wave) must travel through the material to transmit force. This model helps predict the speed of force transmission and provides insight into why solid objects do not behave as ideal rigid bodies.

15:04

📐 One-Dimensional Sound Wave Transmission

The fourth paragraph discusses the concept of one-dimensional sound wave transmission in thin bars, contrasting it with the three-dimensional longitudinal speed of sound. It explains the importance of the Poisson ratio in calculating the speed of sound in materials and how it affects the velocity of a sound wave. The paragraph details the experimental process of determining the correct speed of sound in the steel bar, highlighting the challenges faced and the eventual realization that the extensional speed of sound, specific to one-dimensional objects, was the correct measure to use.

20:05

🎉 Conclusion and Reflection on the Experiment

The final paragraph wraps up the video script by reflecting on the experiment and the insights gained from it. It emphasizes the importance of understanding the atomic structure of materials and the transmission of sound waves in explaining the behavior of solid objects. The paragraph also celebrates the successful application of the one-dimensional sound wave model in predicting the delay in force transmission through the steel bar. The video concludes with a nod to the satisfaction of solving a complex problem and the joy of applying the same physics models to different scenarios.

Mindmap

Keywords

💡Solid Object

A solid object, as introduced in the script, refers to a material with a definite shape and volume that cannot flow like a liquid or a gas. The video uses a bar of steel as an example of a solid object to explore the concept of how force is transmitted through solids. This concept is central to the video's theme, as it challenges the common perception of solids as rigid and unyielding, showing instead that they can transmit force and motion in complex ways.

💡Rigid Body Approximation

The rigid body approximation is a simplification used in physics where an object is considered to be perfectly rigid, meaning it doesn't deform under the application of forces. This approximation is useful for analyzing the motion of objects in classical mechanics but does not account for the internal structure or material properties of the object. In the video, this concept is contrasted with the more complex reality of how materials like steel actually behave when forces are applied, leading to a nuanced understanding of the transmission of force and motion.

💡Quantum Mechanical Wave Function

A quantum mechanical wave function is a mathematical description used in quantum mechanics to calculate the probability of finding a particle in a particular state. It is a fundamental concept in quantum physics that provides a detailed understanding of the behavior of particles at the atomic and subatomic level. In the context of the video, the wave function is mentioned as the most accurate but also the most complex way to model the behavior of the steel bar, highlighting the trade-off between accuracy and practicality in physical models.

💡Speed of Sound

The speed of sound is the distance that a sound wave travels through a medium (like air, water, or a solid material) in a given amount of time. It is dependent on the medium's properties, such as density and elasticity. In the video, the speed of sound in the steel bar is a key factor in determining how quickly the force from pushing on one end is transmitted to the other end. The experiment measures this speed and finds it to be approximately 180 microseconds for a 91-centimeter steel bar.

💡Body Centered Cubic

Body centered cubic (BCC) is a type of crystal structure where atoms are arranged in a lattice with each atom at the corner of the cube and an additional atom at the center of the cube. This structure is common in metals like iron and steel. The BCC structure is relevant in the video because it provides a model for understanding how steel behaves when force is applied, with atoms connected as if by springs, allowing for the transmission of force through the material.

💡Elastic Deformation

Elastic deformation is a type of material deformation where the material changes shape under an applied force but returns to its original shape once the force is removed. This behavior is temporary and reversible. In the video, the concept of elastic deformation is used to explain how the steel bar moves and transmits force when pushed, likening the atomic bonds to springs that compress and then return to their original length.

💡One-Dimensional

In the context of the video, one-dimensional refers to the transmission of sound or force along the length of the steel bar without considering its width or height. The video explains that the speed of sound in a thin bar is different from that in a larger, three-dimensional object because the transmission is one-dimensional, affecting how the force moves through the material.

💡Extensional Speed of Sound

The extensional speed of sound is the velocity at which a sound wave travels longitudinally through a thin, one-dimensional medium like a rod or wire. It is different from the longitudinal speed of sound, which would apply to a three-dimensional medium. In the video, the extensional speed of sound in steel is the key factor in determining the delay in force transmission along the steel bar.

💡Poisson Ratio

The Poisson ratio is a measure of the deformation of a material in response to an applied force. It describes the ratio of the transverse strain to the axial strain. In the context of the video, the Poisson ratio is important for calculating the speed of sound in a material, especially when considering the one-dimensional transmission of sound waves through a thin bar.

💡Force Transmission

Force transmission refers to the process by which a force applied to one part of a system is conveyed to other parts of the system. In the video, force transmission is central to the experiment, as it explores how pushing on one end of a steel bar results in movement at the other end. The video investigates the speed and nature of this transmission, challenging common assumptions about the rigidity of solids.

💡Material Properties

Material properties are the physical and chemical characteristics of a substance that determine its behavior under various conditions. In the video, material properties such as the atomic structure, the speed of sound, and the Poisson ratio of steel are crucial for understanding how the steel bar responds to force. These properties are used to explain the observed phenomena and to make predictions about the behavior of the bar.

Highlights

The experiment explores the concept of how force is transmitted through a solid object, specifically a steel bar.

A thought experiment is proposed where a steel bar is scaled up to 300,000 kilometers, the distance light travels in one second.

The question posed is how long it would take for an observer at the end of the bar to see the bar move after it is pushed.

The discussion includes the possibility that the speed of light, sound, or a combination of material properties could affect the delay.

The experiment is conducted with a 91-centimeter steel bar, a force sensor, and a hammer to measure the delay in force transmission.

The results show a delay of 180 microseconds, which corresponds to the speed of sound in the steel bar.

The atomic structure of steel is discussed, with iron atoms arranged in a body-centered cubic structure.

Electrons in steel act like springs, providing a model for understanding elastic deformation and the transmission of force.

The speed of sound in the steel bar is found to be approximately 5,000 meters per second, which is less than the expected 6,000 meters per second.

The discrepancy in the speed of sound is explained by the Poisson ratio and the one-dimensional nature of the thin steel bar.

The extensional speed of sound is introduced as the relevant speed for the thin steel bar, as opposed to the longitudinal speed.

The experiment demonstrates that solid objects are not ideal rigid bodies, as evidenced by the delay in force transmission.

The importance of using approximate physics models is highlighted, as they allow for practical application and understanding of complex phenomena.

The video emphasizes the value of recycling underlying mathematical machinery across different physics scenarios.

The process of troubleshooting and refining the experimental setup is discussed, including issues with piezoelectric sensors.

The experiment concludes with the correct measurement of the speed of sound in steel, validating the initial prediction.

The video showcases the complexity of seemingly simple demonstrations and the iterative process of scientific inquiry.

Transcripts

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Related Tags

PhysicsExperiments SolidObject ForceTransmission SpeedOfSound MaterialScience SteelBar RigidBody QuantumMechanics ElasticDeformation MechanicalWaves