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8.01x - Lect 6 - Newton's Laws

Lectures by Walter Lewin. They will make you ♥ Physics.・28 minutes read

Acceleration is caused by a push or pull, expressed in Newton's Laws from Newton's First Law to Newton's Third Law. Practical applications of these laws in real-world scenarios like hanging objects demonstrate the universality and relevance of Newton's principles.

Insights

  • Newton's Laws of Motion, including the concepts of acceleration, force, and action-reaction pairs, form the foundational framework for understanding physical interactions and motion in the universe.
  • Practical applications of Newton's laws, such as determining tensions in hanging objects through experimentation and analysis, demonstrate the real-world relevance and universality of these fundamental principles in solving complex problems and explaining natural phenomena.

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Recent questions

  • What is the significance of Newton's First Law in physics?

    Newton's First Law, also known as the law of inertia, states that objects at rest will stay at rest, and objects in motion will continue moving at a constant velocity unless acted upon by an external force. This law is fundamental in understanding the behavior of objects in the absence of forces and serves as the basis for Newton's other laws of motion. It highlights the concept of inertia, where objects resist changes in their state of motion unless influenced by an external force.

  • How does Newton's Second Law relate force and acceleration?

    Newton's Second Law of motion states that the force acting on an object is equal to the mass of the object multiplied by its acceleration. This relationship is expressed as F = ma, where F represents force in newtons, m is the mass of the object in kilograms, and a is the acceleration in meters per second squared. This law provides a quantitative measure of how forces affect the motion of objects and is crucial in understanding the dynamics of various systems.

  • What does Newton's Third Law state about forces in physics?

    Newton's Third Law of motion states that for every action, there is an equal and opposite reaction. This means that when one object exerts a force on another object, the second object exerts an equal force in the opposite direction. The law highlights the symmetry of forces in interactions between objects and plays a significant role in explaining various phenomena, such as the recoil of a gun or the propulsion of a rocket.

  • How can Newton's laws be practically applied in real-world scenarios?

    Newton's laws of motion can be practically applied in real-world scenarios to solve problems involving forces and motion. For example, in determining tensions in hanging objects, the principles of Newton's laws can be used to analyze the forces acting on the system and achieve equilibrium. By decomposing forces into components and solving equations, the tensions in strings supporting objects can be calculated based on their masses and angles. This practical application showcases the universality and relevance of Newton's laws in understanding and predicting the behavior of physical systems.

  • What experimental setups can be used to demonstrate Newton's laws?

    Experimental setups involving hanging objects, tension meters, and calibrated scales can be used to demonstrate Newton's laws of motion in action. By hanging objects of known masses and measuring the tensions in supporting strings, the principles of equilibrium and force distribution can be observed. Through a series of trials and adjustments, the behavior of forces in systems can be studied, challenging expectations and highlighting the fundamental physics principles outlined by Newton's laws. These experiments provide tangible examples of how forces interact in physical systems and validate the theoretical framework established by Newton.

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Summary

00:00

Newton's Laws: Acceleration, Inertia, and Reaction

  • Acceleration is caused by a push or pull, expressed in Newton's Laws.
  • Newton's First Law states that objects at rest remain at rest or in motion at a constant velocity unless acted upon by an external force.
  • Newton's First Law does not hold in all reference frames, specifically not in an accelerating frame.
  • An inertial frame of reference is one without any accelerations, which is rare due to various forces like gravity.
  • The acceleration due to Earth's rotation is 0.034 m/s^2, much smaller than gravitational acceleration.
  • Newton's Second Law states that force equals mass times acceleration, with units of kg*m/s^2, called a newton.
  • The Second Law only holds in inertial reference frames and cannot be proven but is believed due to experimental consistency.
  • Mass can be determined without gravity, validating the Second Law.
  • Newton's Third Law states that for every action, there is an equal and opposite reaction.
  • In a simple example with two objects, a force of 20 N results in an acceleration of 1 m/s^2 for the system, with object 1 exerting a force of 15 N on object 2.

18:45

Newton's Laws in Practical Applications

  • Newton's Second Law states that if one object pushes on another, the force exerted is labeled as F21.
  • Object one is accelerating at a rate of one meter per second squared, leading to the equation F1 + F21 = m1 * a, resulting in F21 being -15.
  • F21, with a magnitude equal to F12, represents the force with which object two pushes back on object one.
  • The Third Law of Newton is exemplified in the consistent forces exerted by two objects on each other, with opposite signs.
  • Everyday experiences like a garden hose snaking back or a balloon flying off illustrate the concept of action equaling minus reaction.
  • The recoil of a gun, a rotating device powered by steam, and walking on different surfaces further demonstrate Newton's Third Law.
  • Hero's engine, a historical invention, can be recreated using a soda can with holes to showcase action equaling minus reaction.
  • A detailed example involving hanging an object on two strings at different angles is used to apply Newton's laws practically.
  • By decomposing forces into x and y components and solving equations, the tensions in the strings can be calculated based on the mass of the object.
  • The practical application of Newton's laws in solving real-world problems, like determining tensions in hanging objects, showcases the universality and relevance of these principles.

38:21

Balancing Forces: Tension Experimentation for Equilibrium

  • Experimentation with forces and angles is demonstrated, aiming to achieve equilibrium.
  • By flipping forces, T1 and T2 are adjusted to balance the system, resulting in a net force of zero.
  • Measurement of tension is challenging, involving tension meters and calibrated scales.
  • A practical example involves hanging four kilograms to measure tension accurately.
  • A detailed experiment with two strings and a two-kilogram block showcases tension distribution.
  • Through a series of trials, the bottom string breaks first, challenging expectations and highlighting physics principles.
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