Newton's 3rd Law Explained with Skateboard, Rocket

Summary

The video explains Newton's Third Law of Motion through engaging demonstrations. It starts with a simple example of leaning on a desk, illustrating how action and reaction forces maintain balance. The speaker then discusses how a balloon accelerates when air is expelled, showcasing the principle in action. A liquid nitrogen experiment highlights jet propulsion, as gas expelled from a heated bottle causes it to spin. Finally, a thrilling skateboard experiment using a fire extinguisher serves as a practical application of the law, where the force of the gas pushes back, demonstrating the dynamic nature of Newton's principles.

Takeaways

• 😀 Newton's third law states that for every action, there is an equal and opposite reaction.
• 🧑‍🔬 Leaning on a desk demonstrates the balance of forces: as you push down, the desk pushes back with equal force.
• 💨 When a balloon accelerates, it is due to forces acting upon it, particularly the air pressure inside pushing outwards.
• 🚀 The expulsion of air from a balloon creates a reaction force that accelerates the balloon in the opposite direction.
• 💧 Filling a plastic bottle with liquid nitrogen and warming it up creates a pressure differential that forces gas out.
• 🔄 The reaction from gas being expelled from the bottle causes it to spin, demonstrating Newton's third law in action.
• 🔥 A jet engine operates on the principle of pushing gas out to generate thrust in the opposite direction.
• ⚠️ The setup with a fire extinguisher and skateboard illustrates a dramatic demonstration of force and reaction.
• 🚀 When the valve of the fire extinguisher is opened, the rapid release of gas creates significant acceleration.
• 🎉 Physics can be fun and engaging, as demonstrated by using liquid nitrogen and a skateboard to visualize concepts.

Q & A

What is Newton's Third Law of Motion?

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

How does leaning on a desk illustrate Newton's Third Law?

When a person leans on a desk, they exert a downward force on the desk. In response, the desk exerts an upward force that is equal and opposite, preventing the person from falling.

What happens when someone pushes harder on a desk?

If a person pushes harder on the desk, they experience acceleration away from it due to the desk pushing back with an equal and opposite force, demonstrating the reaction aspect of Newton's Third Law.

How does a balloon accelerate when air is expelled?

As the balloon releases air, it pushes the air out, which creates a reaction force that pushes back on the balloon, causing it to accelerate in the opposite direction.

What role does pressure play in the liquid nitrogen experiment?

In the liquid nitrogen experiment, the pressure inside the bottle increases as it heats up, forcing gas out through angled vents, which creates a reaction force that propels the bottle in the opposite direction.

How does the plastic bottle act like a jet engine in the demonstration?

The plastic bottle acts like a jet engine because the high pressure inside forces gas out, and the reaction force from the escaping gas pushes the bottle in the opposite direction, illustrating jet propulsion.

What safety precautions were mentioned regarding the fire extinguisher used in the experiment?

The demonstration highlighted that every reduction valve in the fire extinguisher had been removed, making it a potentially dangerous device since it could empty rapidly.

What is the expected outcome when the fire extinguisher valve is cracked open?

When the fire extinguisher valve is cracked open, the gas will be expelled quickly, producing a strong reaction force that should propel the speaker on the skateboard forward.

Why is the concept of action-reaction pairs important in physics?

Action-reaction pairs are crucial in physics because they explain how forces interact and affect motion, allowing us to understand and predict the behavior of objects in various scenarios.

What educational purpose does this demonstration serve?

This demonstration serves to teach students about Newton's Third Law in a practical and engaging way, illustrating complex concepts through visual and physical examples.