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90

Having my own 6-year-old and having successfully explained this, here's my advice from experience: Don't try to explain gravity as a mysterious force. It doesn't make sense to most adults (sad, but true! talk to non-physicists about it and you'll see), it won't make sense to a 6yo. The reason this won't work is that it requires inference from general ...


65

The Foucault pendulum is a great experiment which does demonstrate that the Earth is rotating, but it was only introduced in 1851. The Earth had been known to rotate for several centuries before that, probably stimulated by Copernicus and Galileo pushing the heliocentric model of the solar system during the 16th century. A couple of decades before Faucalt's ...


53

Hiroshima exploded 67 terajoules of energy i.e. $6.7\times 10^{13}$ joules. We may calculate the mass of the Russian meteor assuming that the speed is $v=20,000$ m/s: $$ \frac{1}{2} mv^2 = 6.7 \times 10^{13} $$ We obtain 335 tons. The numbers aren't precise but they're in the ballpark and reasonable. The Russian academy of sciences actually estimates 10,000 ...


49

Foucault pendulum. I don't know how the ancients did it, but it is surely pure classical mechanics. The animation describes the motion of a Foucault Pendulum at a latitude of 30°N.


43

The moon does not fall to Earth because it is in an orbit. One of the most difficult things to learn about physics is the concept of force. Just because there is a force on something does not mean it will be moving in the direction of the force. Instead, the force influences the motion to be a bit more in the direction of the force than it was before. ...


38

Barring whatever fantastic energies would be required to stop the mass of the Earth from rotating and then changing the direction of the rotation, one of the major things I can see changing would be the expectations of weather patterns. Part of what affects our weather is known as the Coriolis Effect. While there would certainly be effects from the ...


32

I generally take "foreseeable future" to mean "in my lifetime" in which case the answer is No. However, if you are really asking, "What does science say about the solidification of earth's core?" then we can answer this. In the core of the planet, we actually have this pretty picture: The core is heated by radioactive decays of Uranium-238, Uranium-235, ...


30

Briefly: Because the moon's orbit "wobbles" up and down, so it isn't always in the plane of the earth's orbit around the sun. There's a 2D plane you can form from the ellipse of the earth's orbit and the sun. This plane is known as the ecliptic. The moon's orbit is not exactly in the ecliptic at all times; see this (slightly overcomplicated) picture from ...


28

Simplest, you say? There are two that strike me as being simple to demonstrate. Luckily someone on the internet has already spent some time to help us here to make these easy to illustrate: Shadows differ from place to place: Eratosthenes carried out this experiment to determine the circumference of the Earth, already assuming its spherical shape; ...


26

The atmosphere of the Earth is mainly composed of nitrogen (N2, 78%) and oxygen (O2, 21%) molecules, which together make up about 99% of its total volume. The remaining 1% contains all sorts of other stuff like argon, water and carbon dioxide, but let's ignore those for now. As you probably know, the oxygen we breathe is produced by plants from water and ...


22

The other answers provide a first-order approximation, assuming uniform density (though Adam Zalcman's does allude to deviations from linearity). (Summary: All the mass farther away from the center cancels out, and gravity decreases linearly with depth from 1 g at the surface to zero at the center.) But in fact, the Earth's core is substantially more dense ...


21

Correct. If you split the earth up into spherical shells, then the gravity from the shells "above" you cancels out, and you only feel the shells "below" you. When you are in the middle there is nothing "below" you. Refrence from Wikipedia Gauss & Shell Theorem. {I am using some simplistic terms, but I don't want to break out surface integrals and ...


20

Those code names all come from certain catalog. For example, NGC means 'New General Catalogue'. There are various catalogs aiming at different objects, like stars, nebulae, galaxies, etc, but not for the Earth, at least not yet. You can find almost all known astronomical catalogs and tables at CDS


19

I suspect the question may be unanswerable, and possibly even meaningless. As I understand it, the giant impact that resulted in the formation of the Moon would almost certainly have also completely liquefied whatever crust the Earth had at the time, producing a global "magma ocean". Thus, there would've been no traces of the impact left — or rather, ...


19

The day/night cycle is the first obvious effect: Days and nights would both be longer (EDIT Or shorter, apparently I got it backwards) if the speed of rotation is the same. All life on the surface of the planet has evolved for day/night cycles of roughly the length we experience now, with leeway for the difference between summer and winter. A sudden ...


18

This is a really rough calculation that doesn't take into account the realistic direction of the bow shock, or calculation of the drag force. I just take the net momentum flow in the solar wind and direct it so as to produce the maximum decceleration and see what happens. Apparently the solar wind pressure is of the order of a nanoPascal. As I write this ...


18

Rub a balloon with a cloth to induce a charge which will demonstrate "static cling", then attract small pieces of paper with the balloon. Once they see that static electricity attracts the small pieces of paper to the bottom of the balloon, then you can start explaining to them about 'the force'.


16

The simplest way to think about it is that there is mass all around you in the center of the Earth so you get an equal gravitational "pull" from all directions. The pulls cancel out so you get no acceleration. If one assumes constant density for the Earth (which isn't strictly speaking true but it is close enough for this illustration) the gravitational ...


16

On the earth-sheltering question, the answer is yes, using material to increase the thermal mass of structures would work just as well on the Moon as on Earth. There might be minor differences due to different materials and lack of water in Moon soils but the general principal would still apply. As for the Moon's core still containing significant heat, ...


16

I think the Foucault pendulum is the best answer, but for the sake of variety I'll add another very interesting one: the equatorial bulge affecting the figure of the Earth. This is the "pancaking" of the planet due to its rotation. You can measure the geometry of the Earth without leaving its surface, and find that it is bulging in accord with your ...


16

Yes, helium can leave the Earth, and yes, we will run out of helium, but because of different reasons. When you buy a helium balloon and its contents get released, this helium goes into the atmosphere. It isn't gone, and it could in principle be purified out of normal air. However, the total amount of helium in the atmosphere is so small it is ...


15

Here are some ideas: a) Try to make her understand the concept of "force" : tie two balls on an elastic band. Make her pull them apart so that she gets a feel of force. Take an apple and drop it. Let her understand that if a force ( her hand) does not hold an object it is pulled by the earth, the way the elastic pulls the balls. b) Then show her on a ...


14

Well, for the basics of the Foucault pendulum, this wikipedia page does an adequate job describing how it works (Specifically read up on the Precession as a form of parallel transport section). This page also has a nice explanation of how they work: A Foucault pendulum is just like any other pendulum, nothing more than a weight attached to a wire; but ...


13

The Moon's orbit is inclined with respect to the Earth's orbit. In other words, if you imagine a Sun, Earth, and Moon model sitting on a tabletop, the Sun would sit approximately still and the Earth might slide around the desktop, while the Moon would orbit the Earth, hopping up off the table, and sinking back down into it. (I used to do this demonstration ...


13

The Moon moves at about a thousand metres per second, but it's a long way away so it only appears to move slowly. Most of the apparent movement of the Moon is actually due to the rotation of the Earth. We see it appearing to go round the Earth once a day, but it actually takes about 28 days to complete an orbit. The Wikipedia article on the Moon's orbit has ...


13

From conservation of angular momentum we have $(I+\Delta I)(\omega+\Delta \omega) = I\omega,$ or $$\frac{\Delta \omega}{\omega} = - \frac{\Delta I}{I+\Delta I} \simeq -\frac{\Delta I}{I}.$$ We make the following simplifying assumptions: The earth is a sphere of uniform density of mass $M$ and radius $R$. The building is constructed on the equator by ...


13

"Total energy of the Earth" is somewhat of an odd concept, but there's no reason we can't really entertain it. It brings up some genuinely difficult questions. The right way to approach this is to define the system correctly and then identify forms of energy content and flows. Things to "count" in the Earth's energy: Heat content Nuclear energy ...


13

Take a magnet and hold it vertically, sprinkle iron fillings on either side of the pole. Iron fillings on the bottom side will be hanging. Then the child will get a feel that, it is possible for things to stay without falling down. You need not explain the concept of gravity for the child now. The child will create the explanation for itself (might also ...



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