Newton's Third Law of Motion Explained | Physics in Motion

Summary

This segment of 'Physics in Motion' explores the forces involved when an arrow is shot from a bow, emphasizing Newton's Third Law of Motion: for every action, there is an equal and opposite reaction. It illustrates how the bow exerts a force on the arrow while the arrow pushes back on the bow. The discussion includes calculations of acceleration differences based on mass, along with real-world examples like skydiving and rocket launches, highlighting action-reaction pairs. This engaging exploration of forces provides insights into the mechanics behind motion, inviting viewers to further explore the concepts presented.

Takeaways

• 🎯 The bow is a crucial component in the motion of an arrow, working in conjunction with the string to propel the arrow forward.
• ⚖️ Newton's Third Law of Motion states that for every action, there is an equal and opposite reaction, demonstrated by the forces between the bow and arrow.
• 📊 The relationship between mass and acceleration is explained by Newton's Second Law, where force equals mass times acceleration (F = ma).
• 🚀 The arrow accelerates at 1280 m/s² while the bow only accelerates at 32.0 m/s² due to the differences in their masses.
• 🌍 In the sky diver example, the Earth and diver exert equal forces on each other, but the diver accelerates much more because of the Earth's larger mass.
• 🔄 Action-reaction pairs can be observed in everyday activities, such as walking, swimming, and rocket launches.
• 🔗 When a sky diver jumps, the action of the jump and the Earth pulling back exemplifies the principle of action-reaction pairs.
• 💨 Once the arrow is released, it no longer experiences horizontal acceleration, as the bow has completed its function.
• 🌌 Gravity continuously pulls on the arrow after release, creating another action-reaction force between the arrow and Earth.
• 📚 Understanding these principles helps explain how forces work together to influence the motion of objects in various scenarios.

Q & A

What happens when an archer releases the string of a bow?

When the archer releases the string, the force from the string propels the arrow forward while simultaneously exerting an equal and opposite force on the bow, causing it to move slightly backward.

How does Newton's Third Law of Motion apply to the bow and arrow?

Newton's Third Law states that for every action, there is an equal and opposite reaction. In the case of the bow and arrow, when the bow exerts a force on the arrow, the arrow exerts an equal force back on the bow.

What are action-reaction pairs, and can you provide examples from the transcript?

Action-reaction pairs are forces that occur in opposite directions between two objects. Examples include: the force of a sky diver pulling on Earth while Earth pulls on the sky diver, and a swimmer pushing against the water while the water pushes back on the swimmer.

Why does the arrow accelerate much more than the bow when released?

The arrow accelerates more than the bow because it has a smaller mass. According to Newton's second law (F = ma), a smaller mass can experience greater acceleration when the same force is applied.

What is the mass and acceleration of the arrow used in the example?

The arrow has a mass of 0.10 kilograms and an average acceleration of 1280 meters per second squared.

How do you calculate the acceleration of the bow when the arrow is released?

The acceleration of the bow can be calculated using the formula: acceleration of the bow = -(mass of the arrow * acceleration of the arrow) / mass of the bow. Plugging in the values gives an acceleration of -32.0 meters per second squared.

What does the term 'free fall' refer to in the context of a sky diver?

Free fall refers to the state of a sky diver as they fall toward the Earth, where they are subject to gravitational force. The Earth pulls them down, and they also exert a pull on the Earth, albeit much smaller due to the Earth's larger mass.

How does gravity affect the motion of the arrow after it leaves the bow?

After the arrow leaves the bow, there is no more horizontal force acting on it, so it does not experience horizontal acceleration. However, gravity continues to act on the arrow, pulling it downward.

What role do combustion gases play during a rocket launch?

During a rocket launch, the combustion gases generated by the rocket engine exert a force on the rocket, pushing it upward. Simultaneously, the rocket exerts an equal force back on the gases, contributing to the rocket's lift-off.

What is the significance of understanding forces working in pairs in physics?

Understanding forces working in pairs helps explain how objects interact with one another and move in response to these forces, which is essential for analyzing motion in various physical contexts.