Fisika SMA - Hukum Newton (4) - Hukum 3 Newton, Gaya Aksi Reaksi (I)

Summary

In this educational video, Kak Imam explains Newton's Third Law of Motion, which states that for every action, there is an equal and opposite reaction. Using real-life examples like normal forces between objects and tension in ropes, the video walks viewers through various physics problems, illustrating the concepts clearly. From understanding the forces acting on objects in contact to solving problems involving multiple masses and forces, the video provides a practical and engaging way to learn about action-reaction force pairs. Viewers are encouraged to subscribe and follow along for more lessons on Newton's laws.

Takeaways

• 😀 The video covers Newton's Third Law of Motion, explaining the concept of action and reaction forces.
• 😀 Action and reaction forces are equal in magnitude but opposite in direction, as shown in examples such as objects on the floor or a tensioned rope.
• 😀 Newton's Third Law is demonstrated with practical examples: a block on the floor, the interaction between two blocks connected by a rope, and gravitational forces acting on objects.
• 😀 The video stresses that every force has a corresponding reaction force, which is crucial to understanding how forces balance in physical systems.
• 😀 A key example discussed is the normal force (N) between objects, such as the force between a block and the floor (N1 and N2).
• 😀 The importance of force diagrams is highlighted, where multiple forces acting on objects are identified and resolved into components for easier calculation.
• 😀 The video explains how to calculate the normal force in various scenarios, such as when an object is at rest on a surface, and the reaction forces are equal and opposite.
• 😀 In problems involving connected objects, the tension forces in ropes are introduced as action-reaction pairs, such as T12 and T21.
• 😀 The script walks through step-by-step problem-solving for calculating forces in a system involving multiple objects (e.g., two or three blocks in contact).
• 😀 Newton's Third Law is reinforced in more complex setups, such as when objects are in motion, and forces must be calculated by resolving them into horizontal and vertical components for clarity.

Q & A

What does Newton's Third Law state about action and reaction forces?

Newton's Third Law states that for every action force, there is an equal and opposite reaction force. This means that if one object exerts a force on a second object, the second object exerts a force of the same magnitude but in the opposite direction on the first object.

How does the concept of normal force relate to Newton's Third Law?

Normal force is the force exerted by a surface to support the weight of an object resting on it. According to Newton's Third Law, if an object exerts a normal force on a surface, the surface exerts an equal but opposite normal force on the object.

Can you explain the action-reaction pair involved when an object is placed on the floor?

When an object is placed on the floor, the object exerts a downward force (its weight) on the floor. Simultaneously, the floor exerts an equal and opposite upward force on the object, known as the normal force.

What happens when two objects are connected by a taut rope, such as in the case of two blocks?

When two blocks are connected by a taut rope, the first block exerts a tension force on the second block, and the second block exerts an equal but opposite tension force on the first block. These forces form an action-reaction pair, as described by Newton's Third Law.

How does the law of action-reaction apply to the gravitational force between Earth and an object?

When an object is near Earth, it experiences a gravitational force pulling it downwards. At the same time, Earth experiences an equal but opposite gravitational force pulling the object upwards. This is the action-reaction pair between the object and Earth.

In the example with two blocks of masses 2 kg and 4 kg, how is the normal force on the second block determined?

To determine the normal force on the second block, we analyze all the forces acting on the block. In this case, the normal force on the second block is the sum of the forces from the contact with the floor and the first block. Using Newton’s Second Law and the given masses, we calculate that the normal force on the second block is 60 N.

In a scenario with two blocks, one with mass 3 kg and the other with mass 7 kg, how is the force of contact between the blocks determined?

The force of contact between the two blocks is determined by calculating the net force on the system and using Newton's Second Law. After considering the forces acting on both blocks, it is determined that the force of contact between the blocks is 10.5 N.

In the case of three blocks in contact and being pushed by an external force, how do you calculate the acceleration of the system?

To calculate the acceleration of the system, we use Newton’s Second Law and sum the masses of all three blocks. The total force acting on the system is divided by the total mass of the system to determine the acceleration. In this case, the acceleration is 3 m/s².

What is the difference between normal force and tension force in the context of Newton's Third Law?

Normal force arises from the contact between an object and a surface, while tension force is transmitted through a rope or string connecting two objects. Both forces obey Newton's Third Law by exerting equal and opposite forces between the objects involved—normal force between the object and the surface, and tension force between objects connected by a rope.

How do we calculate the tension in a rope when two masses are connected and one is pulled by an external force?

To calculate the tension in the rope, we consider the forces acting on each object. We apply Newton's Second Law to each object separately, accounting for the external force and the tension force. By setting up equations for each object, we can solve for the tension in the rope, which in this case is found to be 6 N.