Fisika 1 - Lecture 8-9 Hukum 3 Newton

Summary

This 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.