Explained: 5 Fun Physics Phenomena


– In my last video I showed you five fun physics
phenomena and asked you how they work. You responded with thousands of comments and some
video responses. Well here are my explanations. Let’s start with the cereal because it seems
the simplest but it turns out to be one of the most surprising. The simple explanation
goes like this. So, I showed you cereal is magnetic. I have ground up all of this cereal
into a very fine powder. Let us see what is in it. I’m going to take these strong magnets
and run them over the cereal powder and see if anything is attracted to them. Look how
the cereal actually sticks to the magnet. And it’s because there’s pieces of iron in
this cereal. They’ve been added because iron is something we need, it’s an essential nutrient
that we need to survive. In fact, this cereal has 60% of your recommended daily intake of
iron. But there’s more to it. I received a video response from Maarten Baert showing
non-magnetic objects like plastic and paper also apparently being attracted to a magnet.
So, how does this work? Well water is diamagnetic, which means in the presence of a magnetic
field it generates its own magnetic field in the opposite direction. This means the
water is very slightly repelled by the magnet and this causes a depression in the surface
of the water into which a floating object will slide. You can even see this depression
by looking at the reflections off the water. So cereal is attracted to a magnet due to
its iron content but when floating on the surface of water there is an additional effect,
the depression of the water’s surface due to its diamagnetism. I showed you that you
can find the center of mass of a cane or another stick-type object just by moving your fingers
in towards the middle from the outside. But how does this work, even when you start, in
say, an asymmetric position? Well, one finger is closer to the center of mass and therefore
it carries more of the weight of the cane, and so the friction force between your finger
and the cane is greater until the point where the other finger catches up at which point
this finger slides in and eventually they must meet in the middle. So this a way you
can find the center of mass of any cane or cane-like object. I showed you that if you
trt to flip your phone end over end, there is no way to do it without it also rotating
around the short axis as well. Why is that? The phone has three axes about which it can
rotate. There is the long axis, which has the maximum moment of inertia, meaning it
requires the most torque to accelerate it in that direction. Spinning about the short
axis has the least moment of inertia. Then there is the intermediate axis which has a
moment of inertia in between the other two. Now the intermediate axis theorem says that
if you try to flip any object along its intermediate axis it will not maintain simply that rotation,
it will also get rotations in any of the other directions. That is, if there is any slight
deviation from a perfect rotation. So why does this happen? Well, the mathematics is
kinda complicated but it’s similar to the mathematics of a rigid pendulum. So, if you’re
flipping the phone along its long axis or its short axis the phone acts a little bit
like this pendulum in that any perturbation will cause it simply to go back to where it
was before. But, if you’re flipping it along its intermediate axis it’s as though you’re
trying to balance the pendulum on its end, in which case it’s very unstable and any slight
perturbation may cause it to exponentially increase. So that is why you can’t just flip
your phone along its intermediate axis without it also spinning along one of the other axes.
I showed you that an electrically charged object can deflect a stream of water. But
it is not due to the common explanation, the common reason which is given, which is that
water is a polar molecule. So what really is causing this water to be attracted towards
the cup? Well, it is charges, but it is ions, it is dissolved ions in the water. There will
be some OH ions, some H+ ions and there’ll also be some other impurity ions in the water.
So what happens when you hold this negatively charged cup up against the water’s stream
is it will repel the negative charges, the negative ions in the water, some of which
will go back up into the tap. And that means the water coming down will be slightly positively
charged. And once it breaks up into droplets those droplets have a positive charge that
they can’t get rid of, so now those positive droplets are attracted to the negatively charged
cup. And you can see those droplets swirling around the cup because they are so attracted
to it. So this is not actually a very good demonstration of the polar nature of water.
Even non-polar substances with some ions dissolved in them will deflect in exactly this way.
So this is actually showing us that water droplets are charged, they are charged by
induction, and it is not due to the polar nature of water that they are attracted to
electrically charged objects. Now you know. In the teabag rocket we showed that if you
light a teabag on fire from the top it will actually take off into the air. That happens
because as the teabag is burning all the air inside it heats up and so it expands so it
gets less dense and it’s pushed up by all the cooler air around it. You know, sometimes
people talk about how hot air rises. I mean, that is what hot air does, but only because
the cooler air around it is pushing it up. In essence it’s like a buoyant force because
the hot air is now less dense than the cooler air around it. So, when the teabag burns right
down to the bottom the remaining ash is so light that it gets swept up in that convection
current, and you get a teabag rocket. So do you agree with all of my explanations, and
did you get them right the first time? Let me know in the comments and thanks for watching.

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Comments

  1. The explanation for the water deflecting makes sense to me but my physics and chem teacher told me that wasn't the case and we tried it with distilled water and the water still deflected so it has to be bc of the polar water not bc of the ions in the water

  2. I am from Nepal. Students here are only memorizing definitions written in textbooks. They are not using to explain the real situation. Even our teachers are not good at explaining the real world. People like you Helps us to change the way of thinking and How must be thought about something. I am really proud of you. I love you so much.

  3. so nice i'm a physics student in my third year it is so late to find you
    but i want to ask if we want to know explanation of any action
    what should we do?
    i mean which books are good to search in

  4. whats the meaning of polar nature of water? Isnt it the same like they have opposite ions? or what is it?

  5. But, since the cereal you used is buoyant, wouldn’t the dip in the water cause the cereal to be repelled, as the buoyancy would carry it to the highest point in the water?

    Run-on sentence FTW

    Edit/PS: This would have the opposite effect on objects held up by water tension, as they like to sink to the lowest point in the water.

    Also, a piece of cereal will “run away” from a tack or paper clip that has been put on the surface of water, as it creates a dip in the water at it’s edge.

    Boom, summed up one of Michels videos right there. LOL

  6. One of your explanations was missing an absolute scientific authentication ! It is the one that was talking about the center of mass.
    What if we canceled any reflection force by making the surface of fingers for the conscious person completely smooth ???!!!
    And what if the person himself was not conscious (a robot)?!! it must moving the two fingers perfectly by a constant speed ????!!

    Any explanation must give two scientific detailed answers for two cases, but you have gave us only one answer for the case that you were standing behind !! So.. the second case must depends on the level of the consciousness for the fingers owner.

  7. I did the deflecting water experiment with deionized water. The same effect was observed which leads me to believe that ions were not the cause for the deflection

  8. But the other video you were holding it at center of mass and it fell when the person let go of the other ends for the cane

  9. I have tried to flip phone so it don’t rotate and gotten really mad that I could not do it. Thought I was a bot, turns out just stupid

  10. I know it's a late comment bit can you try to flip it in a vacuum and zero gravity……???or is the result same?

  11. I disagree with the explanation for the water bending. I believe that the reason it is bending is the same as why any neutral object is attracted to a statically charged object. Minute charge separation. The negative charge of the cup, or whatever you have, will repel the electrons in the water molecules slightly causing the side facing the cup to be relatively positively charged and therefore attracted to the negative cup.

  12. I teach physics and when I demonstrate static electricity by rubbing various objects with various fabrics to create positively charged and/or negatively charged objects that then attract or repel each other, I end by doing the following. I place an uncharged cylinder on a flat surface. Then I charge up one of my objects and place it close to the cylinder. The cylinder is always attracted to the charged object. This works for an aluminum can, which suggests that the charge shifts in the conducting aluminum. But a charged object also attracts a non conducting cylinder like a wooden spool or a cork.

    I explain this as the charged object slightly polarizing the atoms nearest the charge and the charge that is repeled from the object is diminished compared to the opposite charge that is attracted to the charged on the object. In other words, the part of the polarized neutral object that is pushed away from the like charge on the charged object has less effect due to increased distance. The part of the polarized charge that is attracted to the charged object dominates because it is slightly closer and hence greater force. I hope that is correct. If not please do a video to explain how a neutral nonconducting object can be attracted to a second object that is highly charged. I claim this is also why a balloon that is charged by rubbing it on hair or cloth will stick to a neutral wall. There is a simulation on PhET that supports the explanation above.

    So I guess this makes me wonder if the polarized charge is in fact contributing to the attraction in the demonstration of water attracted to a charged cup, even if it is not the sole reason.

  13. The cereal has many additives to add weight..for sale..3 billion chinese equals 300million dollars made..resulting in junk fillers in anything china makes.

  14. You are wrong the cup is positively charged ..the water is on a stainless steel with draws a negative ground..the cup is round the water is straight for the water to curl it has to be attracted to the positive cup thus rules of an electro magnet..your school is late.

  15. 3:40 He should said more that unstable state can't be forever due to Heisenberg Uncertainty principle.

  16. It's not the depression the cereal is sliding down into, the cereal floats. It is trying to get to the highest point, so it's the ridge of the water that the cereal is floating to.

  17. This video and the previous one made me smile so damn much. He looks so happy posing these counterintuitive questions and offering neat explanations, which is exactly how I feel when I show my friends cool physics stuff.

  18. I think dark matter is diamagnetic to space ( which is also a spectrum of energy) and that gravity is similar to electromagnetism, but its at much diffrent wavelength. this is where i choke on my own brains, Your welcome

  19. If you're to cheap to buy vitamins just eat a crap load of cereal. Problem solved! He needs to call his water dept.. He's got blood dripping out of his faucets! Cool video though.

  20. i think the explanation of polar water is right.But also there is the effect you are talking about.I think its both.

  21. Veritasium, I am sure you have seen this: https://youtu.be/yFRPhi0jhGc. Another great example of the three axis.

  22. I think you missed the difference between metal iron and ionized iron. You can't exsanguinate a person with a strong magnet just because red blood cells are full of iron. Similarly, you won't find metal iron in cereal unless you melt your spoon in it.

  23. hey there, as someone who was in the military for 10 years as an Air Transporter, finding the center of mass was incredibly important. You can't just throw a bunch of tanks or helicopters on to a C5 and expect it to fly safely. So it was always very important to find that center point, Obviously we couldn't just use our fingers or roll a vehicle on to a pole so there is a formula you can use to find it! As long as you knew the front axle and rear axle weight, you could determine where the center of gravity was. 🙂

  24. I beg to differ: The actual explanation of the cane is another. Keep in mind you ARE trying to balance the cane (unknowingly) so that it won't fall. In that effort there is no other point you will end up but in the center of mass (think about it).

  25. Steave jobs : Hey i made Iphone. Lets make world close.
    Our bro : It have three axis lets rotate it.

  26. I taught that the cereals were "magnetic" because the shown fenomena with the cup was taking place. I taught the water would be slightly raised right in the middle hole in the cereals but i didnt know how did the cup made the water bend. So thats that.

  27. Hey Verisatium , 3:48 – 5:10 ,about the charge of the cup you are talking about. But you are holding the cup with naked hands. Will the cup be not neutralised by earthing then?!

  28. The fourth experiment, does that prove that purely distilled water will not be attracted towards an electrically charged piece ?

  29. For the water attracting to the cup experiment, it is because of water's extremely polar nature. The way that I believe this works is that, through water's inter molecular forces via hydrogen bonding, large water "droplets" (relatively large they are still very very small) form together where, just like a magnet, each side is either positive or negatively charged, due to the dipoles of all the water molecules combining. So, with this droplet of water, the positive end would be attracted to the negative cup more than the negative side would be propelled because the positive side is closer; this is the same way the "positive" side of a magnet moves towards the positive side of another magnet, since the attraction of the magnet's negative side is stronger than the magnets repulsion. So, the water is drawn towards the cup. And i should mention that whether or not the cup is positive or negative doesnt matter

  30. Seeing you balance the cane from below reminded me of something i noticed. When standing one of those silly electric scooters i felt very stable yet getting my center of gravity lower by crouching down i lost stability.

  31. While you need iron for al kinds of chemical pathways in your body, you certainly do NOT need metallic iron. The iron your body can use is iron ion Fe3+ or Fe2+. The addition of metallic iron to cereal then, does more harm then good – but will make it magnetic…Priorities..😅

  32. If it's the ions in water that are attracted the trick won't work if you do it with ion-less water. Distilled water shouldn't contain any ions. Can you reproduce that?

  33. Just found this – nice! I've had some fun with buoyancy, inspired by a common flat-earth misconception that gravity doesn't exist, and is instead relative density. A prominent video dramatically presented an egg. I used a golf ball, and showed that even if it sinks in olive oil, it can be lifted by olive oil because everything in a gas or fluid experiences a buoyant force. For the curious, https://youtu.be/zbMDYEO19k0

  34. 3:41 I done it ones actually. After I watched your video about that I was trying to showing my mom that u can't do trick like that and accidentally that happend xD

  35. I think I'm in love with you. The passion with which you explain so perfectly, in a synthetic way. I want to be just like you.

  36. I do not agree with your tennis racket theorem explanation. I do not know as much as i need to to know how that works but i know for sure its not due to an inconsistency in the way it is thrown. Ive watched a couple videos on the matter and they do not explain it the way you did. It was just too simple…

  37. Tha cane trick was explained by my man Tadashi Tokeida. Look him up people, he is an amazing scientist with an affinity for “toy” physics, if that’s a thing.

  38. I enjoy being re-inculcated with scientific laws, but struggle with retension due to an over abundance of interests, all of which I… Well, I suppose "skim" would be more accurate than "study." For this reason, as well as to make these things more memorable to all, it may be beneficial to show how this knowledge might be put to use in every day applications. In other words, how does knowing these things improve or benefit our lives? But then, maybe you've done that & I just haven't been paying attention… Signed, stroke survivor.
    P.S. Enjoyed seeing you on Smarter Every Day. Thumbs up.

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