Fisika 1 - Lecture 8-9 Hukum 3 Newton

Fisika Udinus

6 Sept 202108:44

Summary

TLDRThis educational video script delves into Newton's Third Law of Motion, illustrating the concept of action-reaction force pairs. It explains that for every force exerted by object A on object B, there is an equal and opposite force exerted by B on A. The script uses examples like a hanging mass, swimming fish, flying birds, and a car's wheels to demonstrate how these forces are applied in various real-life scenarios, emphasizing the importance of this principle in solving physics problems and its applicability within an inertial frame of reference.

Takeaways

📚 Newton's Third Law of Motion is the focus of the video, which states that for every action, there is an equal and opposite reaction.
🔄 The forces of action and reaction are equal in magnitude but opposite in direction, and they act on different objects.
🔗 These forces are known as action-reaction pairs and are fundamental in understanding the interactions between objects.
📐 To be considered an action-reaction pair, four conditions must be met: equal magnitude, opposite direction, collinear, and mutual interaction between two touching objects.
🚫 Non-contact forces, such as gravity, do not require physical contact to exert an action-reaction pair.
📝 The video provides an example of a mass hanging from a ceiling, illustrating the action-reaction forces between the mass, the rope, and the ceiling.
🔍 It is clarified that not all forces acting on an object are part of an action-reaction pair; they must meet the specified conditions.
🌐 The concept of action-reaction pairs is applicable within an inertial reference frame, where the observer is in a non-accelerating frame of reference.
🎯 The video uses real-world examples such as a swimming fish, a flying bird, a car's wheels, and a person firing a gun to demonstrate the application of Newton's Third Law.
💡 The importance of understanding action-reaction pairs is emphasized for solving problems in physics, and it is advised to approach the concept with care and precision.
🌟 The video concludes with a reminder of the significance of Newton's Third Law and a wish for continued learning.

Q & A

What is the third law of Newton's laws of motion?
-Newton's third law states that for every action, there is an equal and opposite reaction. This means that the forces two objects exert on each other are equal in magnitude and opposite in direction.
What are the four criteria that must be met for two forces to be considered an action-reaction pair?
-The four criteria are: 1) They must be equal in magnitude, 2) They must be opposite in direction, 3) They must act along the same line, and 4) They must be the result of an interaction between two touching objects, unless the forces are non-contact forces.
What is the difference between contact and non-contact forces in the context of Newton's third law?
-Contact forces are those that require physical contact between two objects, such as friction or tension in a rope. Non-contact forces, like gravity or magnetic forces, act over a distance without direct contact.
Can you provide an example from the script where Newton's third law is demonstrated with a hanging mass?
-Yes, the script describes a scenario where a mass 'm' is tied to a rope attached to a ceiling. The forces involved are the tension in the rope (T1 and T2) and the gravitational force (W). T1 and T2 are an action-reaction pair because they are equal and opposite, acting on the rope and the mass respectively.
How does the script illustrate the concept of action-reaction forces with the example of a swimming fish?
-The script uses the example of a fish swimming where the fish's action of flapping its fins creates a reaction from the water, which in turn propels the fish forward.
What is the relationship between the forces exerted by a bird flapping its wings and the air?
-When a bird flaps its wings downward, it exerts a force on the air (action). The air then exerts an equal and opposite force on the bird (reaction), allowing it to lift off and fly.
How does the script explain the action-reaction forces in a car's movement?
-The script describes the action of a car's wheels pushing against the ground to the right (action), which results in the ground pushing back to the left on the wheels (reaction), propelling the car forward.
What is the example given in the script to illustrate the action-reaction forces when a balloon is pressed?
-When a balloon is pressed, it exerts a force on the air inside (action). The air inside the balloon then exerts an equal and opposite force on the balloon's walls (reaction), which can cause the balloon to expand or change shape.
How does the script describe the action-reaction forces when a person runs?
-As a person runs, they push down on the ground (action). The ground then pushes back up on the person with an equal force (reaction), allowing them to move forward.
Why is it important to consider the frame of reference when applying Newton's third law?
-It is important because Newton's third law applies to an inertial frame of reference, which is a frame of reference that is not accelerating. The law may not hold true in non-inertial frames where acceleration is present.
What does the script emphasize about the importance of understanding Newton's third law in solving problems?
-The script emphasizes that understanding the concept of action-reaction pairs is crucial for solving problems related to forces and motion, but it also advises to be very careful and consider the conditions under which the law applies.

Outlines

00:00

📚 Newton's Third Law of Motion

This paragraph introduces Newton's third law of motion, which states that every action has an equal and opposite reaction. It explains that these forces are equal in magnitude but opposite in direction, and they act on different objects. The concept of action-reaction force pairs is discussed, along with the conditions that must be met for two forces to be considered an action-reaction pair: equal magnitude, opposite direction, along the same line of action, and resulting from the interaction between two touching objects. The paragraph also provides an example involving a mass attached to a string, illustrating the forces at play and how they are identified as action-reaction pairs.

05:04

🚗 Real-World Applications of Action-Reaction Forces

The second paragraph delves into the real-world applications of action-reaction forces, using various examples to illustrate the concept. It discusses how an action force in one object results in a reaction force in another, as seen in the swimming of a fish, the flapping of a bird's wings, the wheels of a car, and the firing of a gun. The paragraph emphasizes the importance of understanding action-reaction forces in solving problems and reminds us that these forces act on different objects and are only valid within an inertial frame of reference, which is a frame of reference that is not accelerating. The summary concludes with a reminder to be careful and considerate when applying this concept.

Mindmap

Keywords

💡Newton's Third Law

Newton's Third Law of Motion states that for every action, there is an equal and opposite reaction. This law is fundamental to understanding the dynamics of forces in physics. In the video, it is the main theme, explaining how forces interact in various scenarios, such as the force exerted by a fish's fins on water and the reaction force that propels the fish forward.

💡Action-Reaction Force Pair

An action-reaction force pair refers to two forces that are equal in magnitude, opposite in direction, and act on two different objects. The video script uses this concept to illustrate Newton's Third Law, emphasizing that these forces are a result of interactions between objects, such as when a bird flaps its wings and the air pushes back, allowing it to fly.

💡Inertial Frame of Reference

An inertial frame of reference is a non-accelerating frame in which Newton's laws of motion are valid. The script mentions this to clarify that Newton's Third Law applies within such a frame, where an observer does not experience acceleration, ensuring the law's principles hold true.

💡Magnitude

In the context of forces, magnitude refers to the strength or size of the force. The video explains that the action and reaction forces have the same magnitude, which is a key aspect of Newton's Third Law, as seen in the example of a balloon being pressed and the air inside pushing back with an equal force.

💡Direction

Direction in physics defines the line along which a force acts. The video emphasizes that the action and reaction forces are opposite in direction, which is crucial for understanding how they balance each other out, such as the force of a car's wheels pushing against the road and the road pushing back to move the car forward.

💡Contact Force

A contact force is a force that occurs when two objects touch each other. The script mentions that Newton's Third Law applies to contact forces, where the action and reaction forces are a result of direct interaction, like when a person kicks a ball and the ball exerts an equal force back on the person's foot.

💡Non-Contact Force

Non-contact forces act over a distance without direct physical contact between objects. The video script mentions gravity as an example of a non-contact force, where the Earth's gravitational pull acts on objects without touching them, illustrating the broader application of Newton's laws.

💡Free Body Diagram

A free body diagram is a tool used in physics to represent all the forces acting on an object. In the script, it is used to illustrate how to visualize and analyze the forces in a given situation, such as the forces acting on a mass suspended from a ceiling.

💡Galilean Transformation

Although not explicitly mentioned in the script, the concept of Galilean transformation is implied when discussing inertial frames of reference. It is a mathematical transformation that relates the measurements of space and time in two different inertial frames of reference, which is foundational to understanding Newtonian mechanics.

💡Vector

A vector is a quantity that has both magnitude and direction. The script uses the term 'vector' to describe forces, emphasizing that forces are not just about their strength but also the direction in which they act, which is essential for understanding the balance of action and reaction forces.

💡Example

Examples in the video serve to illustrate the concepts being discussed, such as the fish swimming, the bird flapping its wings, and the car moving due to the reaction force from the road. These examples help to make abstract principles more tangible and easier to understand.

Highlights

Introduction to Newton's Third Law of Motion, emphasizing the reciprocal nature of forces.

Explanation of action-reaction force pairs, where the forces are equal in magnitude but opposite in direction.

Clarification that the action-reaction forces act on different objects and are not additive to result in a net force of zero.

Discussion of the four criteria that must be met for a pair of forces to be considered action-reaction forces.

Condition that the forces must be along the same line of action for them to be considered action-reaction forces.

Requirement that the forces must be interactive, meaning they must involve contact unless they are non-contact forces.

Illustration of Newton's Third Law using a mass attached to a string, demonstrating the action-reaction forces involved.

Identification of the action-reaction force pairs in the example of the mass attached to the string.

Explanation of why certain forces in the example, such as the tension in the string and the gravitational force, are not considered action-reaction pairs.

Real-world applications of Newton's Third Law, including the movement of a fish swimming and the flapping of its fins.

Example of a bird flying, where the action of flapping its wings results in an upward reaction force from the air.

Demonstration of how a car's wheels create a reaction force as they push against the road, allowing the car to move.

Explanation of the action-reaction forces involved when a person fires a pistol, with the bullet and the recoil as examples.

Illustration of how pressing a balloon results in the air inside pushing back against the balloon's exterior.

Example of a person running, where the force exerted on the ground results in an upward reaction force, propelling the runner forward.

Emphasis on the importance of Newton's Third Law in solving problems and the need for careful consideration of its application.

Note on the applicability of the concept within an inertial frame of reference, which is a frame of reference without acceleration.

Conclusion of the discussion on Newton's Third Law, with a reminder to study diligently.