Explained: 5 Fun Physics Phenomena

Summary

In this video, the creator revisits five fascinating physics phenomena and explains how they work. These include the magnetic properties of cereal due to iron content, the movement of objects on water due to diamagnetism, finding the center of mass in a stick, the intermediate axis theorem which affects how a phone flips, the deflection of water by charged objects due to dissolved ions, and the teabag rocket propelled by hot air. The explanations reveal surprising insights into common misconceptions and deeper principles at play in everyday occurrences.

Takeaways

• 🧲 Cereal is magnetic because it contains iron, an essential nutrient, which can be detected using strong magnets.
• 💧 Water is diamagnetic, meaning it generates an opposing magnetic field when exposed to a magnet, causing a depression in the water's surface.
• 🌊 Floating objects, like cereal on water, can slide into the depression created by the repelled water surface due to its diamagnetism.
• 🌀 You can find the center of mass of a stick-like object by moving your fingers inward. One finger carries more weight until they meet at the center.
• 📱 Flipping a phone along its intermediate axis results in an unstable motion due to the intermediate axis theorem, causing it to rotate in other directions.
• ⚖️ When flipping along the long or short axis, the phone acts like a pendulum and returns to its original position if perturbed.
• ⚡ An electrically charged object can deflect a stream of water, not because of water's polarity, but due to the movement of ions in the water.
• 💧 Water droplets become slightly positively charged after negative ions are repelled, causing them to be attracted to a negatively charged object.
• 🚀 The teabag rocket effect occurs when hot air inside the burning teabag rises, causing it to lift due to lower density compared to the cooler surrounding air.
• 🔥 The remaining ash from the burned teabag is light enough to be swept up by the convection current, creating the rocket-like motion.

Q & A

What causes cereal to be attracted to a magnet?

Cereal is attracted to a magnet because it contains iron, an essential nutrient that is added during production. The iron particles in the cereal are magnetic, which is why they stick to the magnet.

What additional effect occurs when cereal is floating on water near a magnet?

When cereal floats on water, the diamagnetism of water creates a slight depression in the surface, causing the cereal to slide into it. This effect is in addition to the magnetic attraction due to the iron in the cereal.

Why does water generate its own magnetic field in the presence of a magnet?

Water is diamagnetic, meaning that it generates a weak magnetic field in the opposite direction when exposed to an external magnetic field. This causes it to be slightly repelled by the magnet.

How can you find the center of mass of a cane or similar object using your fingers?

By sliding your fingers inwards from the ends of the cane, the finger closer to the center of mass will carry more weight due to greater friction. As the other finger catches up, they will meet at the center of mass.

Why can't you flip a phone end over end without it rotating around another axis?

This occurs due to the intermediate axis theorem. A phone has three axes with different moments of inertia. When flipped along its intermediate axis, any slight perturbation causes it to rotate along other axes as well, making it unstable.

What causes a charged object to deflect a stream of water?

The deflection is caused by dissolved ions in the water, not its polar nature. A negatively charged object repels negative ions, leaving the water slightly positively charged, which is then attracted to the negatively charged object.

Why is the deflection of water by a charged object not a good demonstration of water's polarity?

The deflection is mainly due to the presence of dissolved ions, not because of water's polar nature. Even non-polar substances with dissolved ions would deflect in a similar way when exposed to a charged object.

What causes the teabag rocket to rise into the air when it is burned?

As the teabag burns, the air inside heats up, causing it to expand and become less dense. The cooler, denser air around it pushes the lighter, hot air upwards, creating a buoyant force that lifts the ash of the teabag into the air.

Why does hot air rise during the teabag rocket demonstration?

Hot air rises because the cooler, denser air around it exerts a buoyant force, pushing the less dense hot air upward. This principle is what causes the teabag rocket to ascend.

What role do ions play in the interaction between a charged object and water droplets?

When a negatively charged object is held near a stream of water, the negative ions in the water are repelled, causing the water droplets to carry a slight positive charge. These positively charged droplets are then attracted to the negatively charged object.