## Sunday 21 October 2012

## Saturday 20 October 2012

### binry destruction

This is inter_activity which should be done in a blog. I will ask a problem, we will discuss, and then solve it.

This one interested me so here it is:

A. The star Sirius (the brightest star in the sky) has a white dwarf companion. Sirius has a mass of about

2 Msun and it is still on the main sequence, while its companion is already a star corpse. Remember that

a white dwarf cant have a mass greater than 1.4 Msun. (Chandrasekhar limit http://en.wikipedia.org/wiki/Subrahmanyan_Chandrasekhar ). Assuming that they both formed on the same

time have a group discuss how Sirius could have a white dwarf companion. HINT: Was the initial mass of the white dwarf star more or lesser than Sirius?

This one interested me so here it is:

A. The star Sirius (the brightest star in the sky) has a white dwarf companion. Sirius has a mass of about

2 Msun and it is still on the main sequence, while its companion is already a star corpse. Remember that

a white dwarf cant have a mass greater than 1.4 Msun. (Chandrasekhar limit http://en.wikipedia.org/wiki/Subrahmanyan_Chandrasekhar ). Assuming that they both formed on the same

time have a group discuss how Sirius could have a white dwarf companion. HINT: Was the initial mass of the white dwarf star more or lesser than Sirius?

### The World From The Eyes of Muhammad Shaheer Niazi: Hi ,I am Muhammad Shaheer Niazi ,welcome to my blo...

The World From The Eyes of Muhammad Shaheer Niazi: Hi ,I am Muhammad Shaheer Niazi ,welcome to my blo...: Hi ,I am Muhammad Shaheer Niazi ,welcome to my blog. I am 12 years old ,my interests are astronomy ,Maths ,physics ,history ,biology and ch...

### NASA new finds on galaxies formation

Simulations such as this will help astronomers better understand the new findings in galaxy evolution. It tracks the development of a single disk galaxy from shortly after the Big Bang to the present day. Colors reveal old stars (red), young stars (white and bright blue) and the distribution of gas density (pale blue); |

credit NASA

for more info to continued answer go here

http://forums.udacity.com/ph100/questions/9173/

my-own-gravity-at-10cm-away-from-me-hehehe-and-

now-black-holes-gravity-to-test-if-light-can-e

scape-one-or-not-and-again-some-more-11-questions-

for-help-in-the-black-hole-question

**Q4. Say a white dwarf has a mass of the sun but the radius of earth.

What is the surface gravity of it? How much will you weigh on it??**

so:

mass = 1.98x10^30 kg

radius = 6.4x10^6

gravitational constant = 6.67x10^-11 Nm/kg^2

a = (G x m)/r^2

= (6.67x10^-11 x 1.98x10^30) / 6.4x10^6^2

= 3224267.5 m/s^2

we will wheigh:

m=40kg

a = 3.22x10^6 m/s^2

f=ma

=40 x 3.22x10^6

=1.28x10^8 N !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

## Friday 19 October 2012

### The python version

Q.1

import math

def cosmic_gravities(mass,radius,constant):

G = 6.67e-11

if constant != G:

return "INCORRECT, >:)"

formula1 = (constant * mass)

formula2 = (radius)**2

main = formula1 / formula2

if constant == G:

return "YOU GOT IT RIGHT ,correct", main

Q.2

def race_with_light_or_a_fly(acceleration,s_light):

light = 300000000 #m/s

if s_light>acceleration:

return "Zap, Ill never let you go you fake programmer!", "P.S its

light and no"

one _meter = 1.057e-16 #LY

if s_light<acceleration:

return "yoyoyoyoyoyo!!!!, light loves you, you and light are going in blackhole"

print cosmic_gravities(40,0.1,6.67e-11)

print cosmic_gravities(1.99e3,5,6.67e-11)

print cosmic_gravities(11212,787,9e-11)

light = 300000000

print race_with_light_or_a_fly(5.7e6,light)

print race_with_light_or_a_fly(5.7e9,light)

Q.3

def escape_velocity(constant, mass, radius):

con = 6.67e-11 #Nm/kg

formulae = (2*constant*mass)/radius

if constant == con:

return "I wanna move it move it , correct", math.sqrt(formulae)/1000

if constant != con:

return "Im falling, im going down, incorrect", False

G = 6.67e-11

print escape_velocity(6.67e-11,79997977979,0.009)

print escape_velocity(6.67e-11,5.34e24,6.4e6)

print escape_velocity(7e8,5555,55555)

Collapse this postimport math

def cosmic_gravities(mass,radius,constant):

G = 6.67e-11

if constant != G:

return "INCORRECT, >:)"

formula1 = (constant * mass)

formula2 = (radius)**2

main = formula1 / formula2

if constant == G:

return "YOU GOT IT RIGHT ,correct", main

Q.2

def race_with_light_or_a_fly(acceleration,s_light):

light = 300000000 #m/s

if s_light>acceleration:

return "Zap, Ill never let you go you fake programmer!", "P.S its

light and no"

one _meter = 1.057e-16 #LY

if s_light<acceleration:

return "yoyoyoyoyoyo!!!!, light loves you, you and light are going in blackhole"

print cosmic_gravities(40,0.1,6.67e-11)

print cosmic_gravities(1.99e3,5,6.67e-11)

print cosmic_gravities(11212,787,9e-11)

light = 300000000

print race_with_light_or_a_fly(5.7e6,light)

print race_with_light_or_a_fly(5.7e9,light)

Q.3

def escape_velocity(constant, mass, radius):

con = 6.67e-11 #Nm/kg

formulae = (2*constant*mass)/radius

if constant == con:

return "I wanna move it move it , correct", math.sqrt(formulae)/1000

if constant != con:

return "Im falling, im going down, incorrect", False

G = 6.67e-11

print escape_velocity(6.67e-11,79997977979,0.009)

print escape_velocity(6.67e-11,5.34e24,6.4e6)

print escape_velocity(7e8,5555,55555)

### The World From The Eyes of Muhammad Shaheer Niazi: My solutions to the Questions written in the book ...

The World From The Eyes of Muhammad Shaheer Niazi: My solutions to the Questions written in the book ...: This I have done for more help in the black hole question:: How much would you weigh on a stellar corpse? Lets calculate what is it rea...

### My solutions to the Questions written in the book .

This I have done for more help in the black hole question::

**How much would you weigh on a stellar corpse? Lets calculate what is it really lie near a white dwarf or Neutron star. First, lets ask how strongly gravity accelerates you on a body (which is a measure of how strongly you are pulled to the surface). the force between two bodies is calculated as**

```
F=(G x M1 x M2)/r^2
```

**Where G is the gravitational constant --- 6.67x10^-11 Nm/kg^2, M1 M2 are the masses of two bodies, and r is there seperation. Also, froom Newtons law,**

```
F = M1 x a
```

**Where a is the acceleration of a body with mass M. So lets consider a situation of a mass - say, you- standing on a body, such as the Earth or a white dwarf. You are M1 and the body you are standing on is M2. The distance between the center of gravity of the body on which you stand is r. The force exerted on you is**

```
F = M1 x a = (G x M1 x M2) / r^2
```

**The acceleration of gravity on that world which is given as the letter g, is (G x M)/r^2. We can now calculate the acceleration of Gravity for our Earth:**

```
g=(6.67x10^-11 x 6x10^24) / (6.4x10^6)
=9.8 m/s^2
```

**The speed you need to get away from a body is escape velocity. It is given by the formula:**

```
v^2=(2 x G x M) / r
```

**For the Earth, v^2 = 2*(6.67x10^-11 x 6x10^24) / 6.4x10^6 = 1.25 x 10^8. Now remembering this is the square of the escape velocity. Taking the square root gives us 11.2 km/s. This is the speed(25,000 mph) that you have to go to escape Earths gravity. The density of a body is its mass over volume. The volume of a sphere is V = 4/3 x pi x r^3, so**

```
d = M/((4/3) x pi x r^3)
= 6x10^24 / (1.33 x 3.14 x (6.4x110^6))
= 5500 KJg/m^3
```

This explanation I took from My great book voyages through the universe 3rd edition from the chp22 Questions.http://www.textbooks.com/ISBN/9780534409050/Andrew-Fraknoi-David-Morrison-and-Sidney-Wolfe/Voyages-Through-the-Universe-and-With-CD-ROM_-_0534409059.php

Now ill answer the questions (figuring out yourself) myself. Aswers are not given in the book.

**Q1.**

**What is the acceleration of gravity at the surface of the sun!?How much greater is it than Earths? How much would you weigh on the sun?**

**My Ans:**

```
Mass of sun = 1.98x10^30 kg
r = 6.96x10^8 m
G = 6.67x10^-11 Nm/kg
```

**so:**

```
g = (G x M)/r^2
= (6.67x10^-11 x 1.98x10^30)/6.96x10^8^2
= 272.6 m/s^2
```

**How much greater:**

```
Earth= 9.8 m/s^2
sun= 272.8 m/s^2
greater = 272.8 / 9.8
= 27.8 times the earth
```

**How much will I weigh:**

```
me = 40 kg
sun g = 272.8
wheight = 272.8 x 40 = 10912N #OMG! I weigh 1.1 tonne
```

**Q2. What is the escape velocity of the sun? How much is it greater than Earths?**

**My Ans:**

```
G = 6.67x10^-11 Nm/kg
M = 1.98x10^30 kg
r = 6.96x10^8 m
```

**so:**

```
v = sqrt(2 x G x M)/r
= 616035.7 m/s = 616 km/s # nice
```

**Q3.what is the density of the sun?**

**My Ans:**

```
V = 4/3 x pi x r^3
d = M/(4/3) x pi x r^3
v = 4/3 x 3.142 x 6.96x10^8
= 1.412x10^27m = 1.412x10^24km
d = 1.98x10^30 / 1.412x10^24
= 1.3943kg/m^2
```

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