Physics explanation to certain common facts

[paereap]

Geez been thinking of these questions for sometime already, but I can't really get an answer and would appreciate some help.

1. The Sun’s gravitational pull on the Moon is greater than that of the Earth’s. But why does the Moon not fly toward the Sun?

2. Why must a geosynchronous satellite orbit around the equator?

3. How do tornados or hurricanes push off roofs of houses? Read somewhere this is due to Bernoulli's Principle, but I don't get why.

4.Why are flywheels solid disks/cylinders and not other shapes?

5. How does spinning an egg tell us whether it is hard-boiled or half-boiled?

Thanks to anyone who will help!

 

[p.mlo]

Some Physics Snacks

2. Becose it will see then the whole Earth from South Pole to North Pole, and satelites can fly slower becose equator is long.

5.If it turnes fast then it's hard boild if slow half-boiled it's related with rotational inertia

 

[ZackG]

Re: Some Physics Snacks

1) If you took the Earth away, "poof," and the Moon were at just that part of the orbit where it were moving in the same direction as the Earth, then it would continue in an Earthlike orbit around the Sun. Since both the Earth and the Moon are revolving around the Sun, at the same distance and speed, they both have a centrifugal force which exactly balances the Sun's gravitational pull on them. You could say they are both in orbit around the Sun together. Then, Earth + Moon is a system in orbit around the sun, and we can consider just the gravitional interaction between the Earth and the moon and disregard the Sun when computing lunar cycles.

2) A Geosynchronous satellite is defined as one whose orbit causes it to reside in exactly one spot above the Earth's surface. It is synchrozined with the Earth (Geo- means Earth; it comes from Greek.) The only place this occurs is when you're an exact distance above the equator. Here's why: First, the velocity of the orbit is determined by the distance from the center of the Earth. Geosynchronous satellites have to be just exactly the distance that gives them a 24 hour orbit. I forget what the exact distance is. You can compute it. Second, the satellite must be moving in the exact same direction that the earth is spinning, or else it will drift. Picture it: Say the satellite starts over the equator but is going north in it's orbit. After six hours, it is over the north pole. Well, it's not over the same spot anymore is it? So it's not geosynchronous. It may still have a 24 hour orbit and not be geosynchronous.

3) I don't know about 3. That's cool if it's true.

4) A flywheel could be any shape. (But it should be symmetric about the axis unless you want some serious vibration issues!) It depends mostly on the materials you're building it with and the factory methods you're using. Sorry, but it is all engineering. From a scientific point of view, the ideal flywheel is a ring of infinite diameter... Basically, you want enough mass away from the axis to store gobs of rotational momentum, but you need enough mass close to the center so that when it spins up to 30,000 rpm, it doesn't fall apart because of the mechanical stresses (even hard steel can take only so much).

5) It does? I'm going to have to try that!

 

[nonlinear]

Re: Some Physics Snacks

(5) In boiled egg, mass is uniformly distributed, while in raw egg content is in liquid state. when we rotate them, the mass distribution of boiled remains the same while that in the raw egg, fluid moves away from axis of rotation. Thus moment of inertia of former will be less than the latter.

 

[nikhilele]

Some Physics Snacks

distance of GeoSyn satellite is near 36000Km from earth surface.

Added after 48 seconds:

and earth radius is near 6400km

 

[Kral]

Re: Some Physics Snacks

paereap,
1) Gravitation force = (1/2)RM1M2/d^2. Where R = the universal gravitational constant. M1 is the mass of one object, M2 is the mass of the other object, d is the distance between the two objects. The product of the moon mass and earth mass is much smaller that the product of the moon mass and the sun mass. However, the distance between the moon and Earth is musch smaller thatn the distance between the moon and the sun, This is the reason that the gravitational force beteen Earth and moon is greater than the gravitational force between the sun and the moon. Look up the masses of the Earth, moon and sun, and the distances beteen the Earth and moon, and the moon and sun (practically the same as the Earth-sun distance. and you will see why this is true.
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2) Answered by ZackG
..
3) Tornados and hurricanes present areas of extreme low pressure. It is the pressure differential between the interior (high) and the exterior (low) that cuases roffs to fly off and walls to tumble outward.
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4) The most efficent flywheels have mass concentrated at the periphery. However, cylindrical flywheels are cheaper to manufacture. By concentrating the mass on the periphery you achiveve a higher polar moment of inertia than with a cylindrical wheel. Because of this you can store more energy for a given rotational speed. E=(1/2)Jw^2, where J = moment of inertia, w is the rotational speed.
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5) Answered by nonlinear.
Regards,
Kral

 

[fguihot]

Re: Some Physics Snacks

5) You should turn the egg quickly, then stop it and let it go.
If the egg start to turn , it's half-boiled.
When you turn it, the inside will turn with the egg.
When you stop it, if the inside is hard-boiled, it will stop with the egg.
If the inside is liquidous, it will continue to turn, due to the low friction coefficient, and liquidous inertia.
Then, when you let it go, it will start to turn, due to the low, but not null friction coefficient of inside liquidous versus the egg inner surface.
In fact, we use the egg liquidous like a kind of inertia wheel to store rotationnal energy...