Why don’t we use giant batteries to power rockets instead of fuel?

Why don't we use giant batteries to power rockets instead of fuel? by Robert Frost

Answer by Robert Frost:

Be careful about the word power. Batteries do power rockets, but they don’t propel rockets. I think your question is about propulsion. You might be thinking about how we have electric cars and we have petroleum fueled cars on Earth and wondering why the same thing can’t happen in space.

Whenever discussing the motion of an object, we should start by refreshing ourselves with Newton’s three laws of motion:

First Law: “Every object persists in its state of rest or uniform motion in a straight line unless it is compelled to change that state by forces impressed on it.”

Second Law: “Force is equal to the change in momentum per change in time. For a constant mass, force equals mass times acceleration.”

Third Law: “For every action, there is an equal and opposite reaction.”

The first law tells us that a spacecraft will continue along its path until forces act upon it instituting a change in the motion. This is the part that a lot of people are confused about when it comes to understanding that spacecraft are not constantly firing their engines. They only fire their engines when they need to make a change or have to counteract an external force.

The third law explains how a car moves down the road, on Earth. The rotating tires experience friction against the ground and push backwards against the ground. For that action, there is an equal and opposite reaction – the car moves forward. Electrical motors can make wheels rotate just as well as a chemical combustion engine can.

In space, there is no ground to grip. There is nothing to push against – wheels are useless, so how do we change the motion of our spacecraft? Let’s look at the second law.

We need a force to accelerate our spacecraft. The second law tells us that a force is equal to a change in momentum per change in time. Messing with the momentum can give us the force we need to accelerate the spacecraft. But there’s another rule of physics we have to consider – conservation of momentum. The total momentum of a system remains the same. So, if we throw some burned fuel out of the back of the spacecraft, the momentum of that gas has to be balanced by an equal and opposite change in momentum of the spacecraft. This is essentially the example you probably saw in sixth or seventh grade of a person in ice skates, on a frozen lake, throwing a ball. When she threw the ball forward, she moved backwards. The speed at which she moved backwards was proportional to the speed the ball moved forward, considering the masses of both the ball and girl.

We throw a small amount of fuel ([math]m_{e}[/math]) out of the back of the spacecraft at high velocity ([math]v_{e}[/math]) and to conserve momentum, our much larger spacecraft ([math]m_{s}[/math]) will travel forwards at a smaller velocity ([math]v_{s}[/math]) such that the magnitude of added [math]mv[/math] for the spacecraft equals the magnitude of [math]mv[/math] for the ejected fuel.

From this, we can derive the rocket equation, also known as the Tsiolkovsky rocket equation:

That equation tells us that the change in velocity of a rocket is equal to the exhaust velocity of the burned fuel times the natural log of the original mass divided by the final mass. We change velocity by changing mass!

Now that we’ve gone through the explanation of how a spacecraft changes its motion, let’s return to your question. You asked “why don’t we use giant batteries to power rockets instead of fuel?

Since there is nothing to push against, in space, in order for us to get our equal and opposite reaction, we have to throw mass out of the back of the rocket. Using the electrical energy of a giant battery doesn’t allow us to manipulate the momentum. This is why chemical rockets are the only way we know how to get to space. If you don’t believe me, let’s ask Elon Musk:

Why don't we use giant batteries to power rockets instead of fuel?


What are some useful websites?

What are some useful websites? by @aashishism

Answer by Aashish Biradar:

  1. ctrlq.org/screenshots – for capturing screenshots of web pages on mobile and desktops.
  2. dictation.io – online voice recognition in the browser itself.
  3. erodollarmovies.com – find full-length movies on YouTube.
  4. goo.gl – shorten long URLs and convert URLs into QR codes.
  5. unfurlr.come – find the original URL that’s hiding behind a short URL.
  6. qClock – find the local time of a city using Google Maps.
  7. copypastecharacter.com – copy special characters that aren’t on your keyboard.
  8. codeacademy.com – the best place to learn coding online.
  9. lovelycharts.com – create flowcharts, network diagrams, sitemaps, etc.
  10. iconfinder.com – find icons of all sizes.
  11. office.com – download templates, clipart and images for your Office documents.
  12. followupthen.com – the easiest way to setup email reminders.
  13. jotti.org – scan any suspicious file or email attachment for viruses.
  14. wolframalpha.com – gets answers directly without searching – see more wolfram tips.
  15. printwhatyoulike.com – print web pages without the clutter.
  16. ctrlq.save – save online files to Dropbox or Google Drive directly.
  17. ctrql.rss – a search engine for RSS feeds.
  18. e.ggtimer.com – a simple online timer for your daily needs.
  19. coralcdn.org – if a site is down due to heavy traffic, try accessing it through coral CDN.
  20. random.org – pick random numbers, flip coins, and more.
  21. pdfescape.com – lets you can quickly edit PDFs in the browser itself.
  22. tubemogul.com – simultaneously upload videos to YouTube and other video sites.
  23. scr.im – share you email address online without worrying about spam.
  24. spypig.com – now get read receipts for your email.
  25. myfonts.com/WhatTheFont – quickly determine the font name from an image.
  26. google.com/webfonts – a good collection of open source fonts.
  27. regex.info – find data hidden in your photographs – see more EXIF tools.
  28. livestream.com – broadcast events live over the web, including your desktop screen.
  29. iwantmyname.com – helps you search domains across all TLDs.
  30. homestyler.com – design from scratch or re-model your home in 3d.
  31. join.me – share you screen with anyone over the web.
  32. onlineocr.net – recognize text from scanned PDFs – see other OCR tools.
  33. flightstats.com – Track flight status at airports worldwide.
  34. wetransfer.com – for sharing really big files online.
  35. Project Gutenberg, Open Library, Google Books, ManyBooks and FeedBooks – are some popular websites that offer a large collection of classics and public domain (copyright expired) books in standard formats like MOBI that you can easily transfer to your Kindle over USB or Wi-Fi.
  36. polishmywriting.com – check your writing for spelling or grammatical errors.
  37. marker.to – easily highlight the important parts of a web page for sharing.
  38. typewith.me – work on the same document with multiple people.
  39. whichdateworks.com – planning an event? find a date that works for all.
  40. everytimezone.com – a less confusing view of the world time zones.
  41. gtmetrix.com – the perfect tool for measuring your site performanceonline.
  42. noteflight.com – print music sheets, write your own music online (review).
  43. imo.im – chat with your buddies on Skype, Facebook, Google Talk, etc. from one place.
  44. translate.google.com – translate web pages, PDFs and Office documents.
  45. kleki.com – create paintings and sketches with a wide variety of brushes.
  46. similarsites.com – discover new sites that are similar to what you like already.
  47. wordle.net – quick summarize long pieces of text with tag clouds.
  48. bubbl.us – create mind-maps, brainstorm ideas in the browser.
  49. kuler.adobe.com – get color ideas, also extract colors from photographs.
  50. liveshare.com – share your photos in an album instantly.
  51. lmgtfy.com – when your friends are too lazy to use Google on their own.
  52. midomi.com – when you need to find the name of a song.
  53. google.com/history – see your past searches, also among most important Google URLs
  54. bing.com/images – automatically find perfectly-sized wallpapers for mobiles.
  55. faxzero.com – send an online fax for free – see more fax services.
  56. feedmyinbox.com – get RSS feeds as an email newsletter.
  57. ge.tt – qiuckly send a file to someone, they can even preview it before downloading.
  58. pipebytes.com – transfer files of any size without uploading to a third-party server.
  59. tinychat.com – setup a private chat room in micro-seconds.
  60. privnote.com – create text notes that will self-destruct after being read.
  61. boxoh.com – track the status of any shipment on Google Maps – alternative.
  62. mondrian.io – create vector drawings in the browser
  63. draw.io – create diagrams and flowcharts in the browser, export your drawings to Google Drive and Dropbox.
  64. downforeveryoneorjustme.com – find if your favorite website is offline or not?
  65. ewhois.com – find the other websitesof a person with reverse Analytics lookup.
  66. whoishostingthis.com – find the web host of any website.
  67. labnol.org – software tutorials and how-to guides.
  68. disposablewebpage.com – create a temporary web page that self-destruct.
  69. urbandictionary.com – find definitions of slangs and informal words.
  70. seatguru.com – consult this site before choosing a seat for your next flight.
  71. unsplash.comdownload imagesabsolutely free.
  72. zoom.it – view very high-resolution images in your browser without scrolling.
  73. scribblemaps.com – create custom Google Maps easily.
  74. alertful.com – quickly setup email reminders for important events.
  75. picmonkey.com – Picnik is offline but PicMonkey is an even better image editor.
  76. formspring.me – you can ask or answer personal questions here.
  77. sumopaint.com – an excellent layer-based online image editor.
  78. snopes.com – find if that email offer you received is real or just another scam.
  79. typingweb.com – master touch-typing with these practice sessions.
  80. mailvu.com – send video emails to anyone using your web cam.
  81. timerime.com – create timelines with audio, video and images.
  82. stupeflix.com – make a movie out of your images, audio and video clips.
  83. safeweb.norton.com – check the trust level of any website.
  84. teuxdeux.com – a beautiful to-do app that looks like your paper dairy.
  85. deadurl.com – you’ll need this when your bookmarked web pages are deleted.
  86. minutes.io – quickly capture effective notes during meetings.
  87. youtube.com/leanback – Watch YouTube channels in TV mode.
  88. youtube.com/disco – quickly create a video playlist of your favorite artist.
  89. talltweets.com – Send tweets longer than 140 characters.
  90. pancake.io – create a free and simple website using your Dropbox account.
  91. builtwith.com – find the technology stack to know everything about a website.
  92. woorank.com – research a website from the SEO perspective.
  93. mixlr.com – broadcast live audio over the web.
  94. radbox.me – bookmark online videos and watch them later (review).
  95. tagmydoc.com – add QR codes to your documents and presentations (review).
  96. notes.io – the easiest way to write short text notes in the browser.
  97. ctrlq.org/html-mail – send rich-text mails to anyone, anonymously.
  98. fiverr.com – hire people to do little things for $5.
  99. otixo.com – easily manage your online files on Dropbox, Google Docs, etc.
  100. ifttt.com – create a connection between all your online accounts.

What are some useful websites?

What is a word people constantly misuse?

What is a word people constantly misuse? by Mandeep Singh Grang

Answer by Mandeep Singh Grang:

You can never depend on the sound of a word to deduce its meaning as there are words which mean nothing what they sound like. Such words are informally called as Phantonyms (phantom + antonym).

Here’s a look at 10 phantonyms in English which are sure to trip even seasoned speakers such as President Obama:

1. Inflammable

The opposite of flammable is non-flammable.

2. Disinterested

The opposite of interested is uninterested.

3. Enormity

Note: If you think enormity also means immensity, please checkout my explanation in the comments section.

4. Suffrage

5. Fulsome

6. Vagitus

7. Phosphene

8. Noisome

9. Restive

10. Minimus

Source: This answer has been reproduced from my full post on my blog Livgently

Also checkout:
10 English Words Which Mean Nothing What They Sound Like

11 English Words Which Are Their Own Opposites

13 English Words That Change Meanings With Pronunciation

What is a word people constantly misuse?

What are some great advertisements?

What are some great advertisements? by Vinay Mittal

Answer by Vinay Mittal:

Google Billboard Puzzle

This is one of the best advertisement cum classified I have ever came across…

In 2004, google came with a brilliant way of recruiting talented people.

They posted a mathematical puzzle on a billboard on 'Highway 101'

in Silicon Valley It read:

{first 10-digit prime found in consecutive digits e}.com."

The answer, http://7427466391.com,

would lead to a Web page with yet another equation to solve, with still no sign of the firm that wanted to recruit some of the best math guys, out there. It wasn't known that it was Google, until the puzzle was cracked. It looked somewhat like

well, in this manner they created a buzz around the valley, resulting into mouth publicity. This was the era when silicon valley was following an ever rising trend and fighting for smart employees.

Thus by posting this, they already shortlisted thousands of applications by placing the ad among the eligible candidates only.

Now if you’re done with brainstorming here's the code for finding the 'First 10 digit prime number in the consecutive digits of e'

import java.math.BigDecimal;
import java.math.MathContext;
public class EulersNumber {
 public static void main(String[] args) {
 BigDecimal e = BigDecimal.ONE;
 BigDecimal bigDecimal = BigDecimal.ONE;
 for(int i=1;i<100;i++) {
 bigDecimal = bigDecimal.multiply(new BigDecimal(i * 1.0 + ""));
 e = e.add(new BigDecimal(1.0 + "").divide(bigDecimal, new MathContext(10000)));
 String strDecimalPart = (e + "").substring(2);
 for(int i=0;i<strDecimalPart.length()-10;i++) {
 long num = Long.parseLong(strDecimalPart.substring(i,i+10));
 if(isPrime(num)) {
 System.out.println("First 10 digit prime number in the decimal part of e : " + num);
 public static boolean isPrime (long n) {
 if (n<=1) return false;
 if (n==2) return true;
 if (n%2==0) return false;
 long m = (long) Math.sqrt(n);
 for (long i=3; i<=m; i+=2)
 if (n%i==0)
 return false;
 return true;

Edits 1 : Whoa! 1K-Upvotes, first ever for me, tons of thanks to each one of you…

What are some great advertisements?

What are some of the best kept secrets of Hyderabad?

What are some of the best kept secrets of Hyderabad? by @GabbarSanghi

Answer by Ratnakar Sadasyula(రత్నాకర్ సదస్యుల):

PS: I have updated this answer, with some more trivia and pictures to make it more interesting.

First things first the city was developed by Quli Qutub Shah, and was patterned after the Iranian city of Isfahan. While Secunderabad gets it's name from Sikandar Jah, the 3rd Asaf Jahi Nizam, and was founded as a British cantonment, in 1806.

A.S.Rao Nagar is named after the founder of ECIL, it is now the fastest growing suburbs in Hyderabad.

The Nizam had a cavalry of African guards, who were given quarters to stay, that area is now called A.C.Guards.

Albert Abid was a Jewish valet of the Nizam, who owned a shop, the surrounding area was named Abids after him, and is now one of Hyderabad's major commercial centers. The GPO is also located here, as well as some of Hyderabad's leading schools too.

Afzalgunj gets it's name from the 5th Nizam Afzal Ud Daulah, who gifted the land to grain merchants here. Now a bustling market place, it is home to State Central Library which has around 17,000 manuscripts dating back to ancient, medieval times. The famous Salarjung museum is also close by.

Aghapura, houses the HQ of the MIM party and is named after Agha Muhammed Dawood the disciple of the Sufi Saint, Abul Ulai.

Alwal gets it's name from the Alwars who settled down here, most of them were devoteess of Lord Venkateswara. The place is famous for it's large Venkateswara Temple, noted director Shyam Benegal is a resident of this area.

Amberpet lying adjacent to Osmania University gets it's name from Hazrat Amber Baba, a famous Sufi saint, whose dargah to date draws a lot of devotees.

Ameerpet gets it's name from Amir Ali, a jagirdar of the Nizam who was gifted the land here. The Nizamia Observatory here was the 3rd such to be setup in India. It is right now famed for it's computer training centers, shopping complexes and shops.

Barkas in the Old City area gets it's name from the fact that it housed military barracks of the Nizam. This place was where the Arab soldiers and bodyguards of the Nizam used to stay, even now their descendants the Chaush, make up a bulk of the population here.

Basheerbagh located in the heart of Hyderabad, Bashir-ud-DauIa Bahadur, a senior noble belonging to the Paigah aristocracy. The Paigah palace is located here too.

Begum Bazar gets it's name from Humda Begum, wife of Nizam Ali Khan Nizamul Mulk who gifted the land here to merchants for their trading activities. It has the 2nd largest fish market in Hyderabad, and the first Ganesh Puja pandal was set up here. Right now one of the major wholesale markets in the city.

Begumpet gets it's name from Basheer Ul-Unnisaa Begum, the daughter of the 6th Nizam who got this land as part of her wedding dowry, it is now one of the major commercial centers in Hyderabad, as well home to some IT firms too. Sir Ronald Ross discovered the cause of malaria, during his work at the Begumpet general hospital in 1897.

Bowenpally is one of the 3 villages that made up Secunderabad, the other two being Alwal and Tirumalgerry. It was named as Bhuvanapalli after Trailokya Bhuvaneswara,an ancient Chalukya ruler.

Chikkadapally gets it's name from the word Chikkad meaning mud, owing to the fact that mud often got deposited here from drain nalas. Has a very old Venkateswara Temple.

Darushifa gets it's name from the large hospital built here by Sultan Quli Qutub Shah, the word means Door to Health.

Dhoolpet was founded by migrants from Uttar Pradesh, who settled here during the Nizam's time. The area is famous for it's Ganesh Idols manufacture, as well as the illegal liquor joints here, a strange mix of crime and religion.

Dilsukh Ram Pershad a land owner near Malakpet subdivided his land into plots and one of them was Dilsukhnagar. Lying on the route to Vijayawada, it has become a bustling commercial hub, also home to many colleges, coaching institutes.

Domalguda, gets it's name from the fact that two wrestlers( Do Malla) lived here, the Ramakrishna Math is located here, and this lies next to Tank Bund.

Habsiguda is named after the Abysinnian guards of the Nizam who were locally referred to as Habsis, they settled here during that time.

Khairtabad is believed to be named after Khairun Nissa, the wife of Capt James Kirkpatrick, mentioned in the book White Mughals by William Dalyrmple. It is famous for the Khairatabad Ganesh, the largest one in Hyderabad during the Ganesh Puja.

Mehboob ki Mehndi, is the city's red light area. Located in old city, quite a notorious place, though closed down of late.

Gowliguda get's it's name from the fact that it was a village of Gowlis( milkmen), it used to have the hangars for the Nizam's private aircraft, now used as a bus repair workshop.

Agoranath Chattopadhyaya the father of Dr.Sarojini Naidu was the first principal of the Nizam College.

Fateh Maidan which houses the Old Cricket stadium, was used as a camping ground by the Mughal Army during their Siege of Golconda. After Golkonda fell to the Mughals, it was named as Fateh Maidan- Ground of Victory.

Bolarum was where Sardar Patel negotiated the terms of the Nizam's surrender with his general El Eldroos.has the Rashtrapati Nilayam, equivalent of the Rashtrapati Bhavan, serving as the official residence of the President, whenever he visits the South.

Hussain Sagar gets it's name from Hazrat Hussain Shah Wali, a renowned Sufi saint of Golkonda in the 16th century, who also built it for the city's water needs.

The Andhra Pradesh Secretariat, is partially housed in the Saifabad Palace, built by 6th Nizam, Mahbub Ali Kha

Niloufer Hospital was built on the request of Princess Niloufer, daughter in law of the last Nizam, she wanted a medical center that would take care of women in their pregnancy and childbirth stage. Niloufer incidentally was one of the last princesses of the Ottoman dynasty. She had also worked as a nurse during WWII.

The Yellama temple in Balkampet is believed to be dedicated to Parashuram's mother Renuka( Yellama), who apparently hid here, to escape being killed by her son. It is one of the main temples for Bonalu.

Tarnaka literally means "Wired Checkpost", it gets it's name from the fact that the place had a Telegraph Office( Tar) here and Naka meaning Checkpost.

Koti gets it's name from the fact that it was primarily a residence for the Nizam's concubines. The mansion used to house the concubines was later converted into a residence for Sir James Kirkpatrick, the lover of Khairunissa who married her.

Moazzam Jahi market or MJ Market was named after the second son Moazzam Jah of the last Nizam. Famous shopping center.

What are some of the best kept secrets of Hyderabad?

How can Communism be explained to a ten year old?

How can Communism be explained to a ten year old? by @balajivis

Answer by Balaji Viswanathan:

Your grandfather comes from a small town called Gori. It was an ordinary town with its own share of pain and pleasure.  Some were rich and some were poor.

Your grandfather owned a farm and a factory. He was the richest guy in town and a somewhat compassionate man. One day, a smart, young man named Joe came to him. The young man was from Vienna and looked erudite.

The young man helped your grandfather understand the level of poverty in the town. Joe also convinced that your grandfather should do something about it. Since we had such a big home, we rented a room in that for free to Joe and his two friends. We cooked them hot food everyday.

After a few months, he brought a few of his other poor friends to home. These people had lost their homes to a snowstorm and needed temporary housing. Since there were not enough rooms, your grandfather asked me and all your uncles & aunts to share the same room.

After a few more months, Joe convinced that the inequality in the house was terrible. The concept of having maids and workers were considered backward. We were all asked to work together as a common group to take care of the home and the farm.  The kids of the poor people worked shoulder-shoulder with us. He called that Communism. It had a lot of ring of egalitarian concepts.  It felt logical and fun as we sang and danced.

A year passed.

Joe came up with a new idea that ownership of things is a bad thing. After all, everything was got from the society around us. That means I had to share my clothes, bicycle, pens and books with the other kids in the house.

My grandfather and rest of family started getting uncomfortable at this. But, we didn't want to disappoint Joe.

My family went for summer vacation to Europe. When we returned, we had a surprise waiting.

Joe had brought a hundred more poor people into the home. All our stuff was moved into one room. Joe said that an average area enjoyed by a person in that village was just 20 sq. ft. Since, we had 10 members in the family we were given a 250 sq. ft room.

People were swarming the mansion and occupied every corner. There was food strewn all over the carpet. The place was a complete mess.

Joe had already taken over your grandfather's study. Joe didn't make a request for any of this. We were just informed. Your grandfather was furious and confronted Joe in the big study. That was the last we heard of your grandfather. Joe's approach was completely changed.

Joe made the announcement that each person would work 14 hours a day until all the poverty is solved. All sorts of private ownership were banned. I would get caned if I even kept a candy in my pocket. I was also made to feel guilty of all the pleasures I got. Soon, a committee was setup to determine what is pleasurable to whom. The TV at home and my favorite bike were taken away.

We kept sinking low and low that the ground floor was completely destroyed. There was stinking smell of toilet. The carpet has now completely gone and the walls had come off.

We had now the Communist wonderland in the village. Although everyone was still poor, there was no more rich either. The only one to enjoy all the wealth  was Joe who now wore the luxury clothes that your grandfather had. He took up the whole of the first floor. He would shoot anyone who climbed the stairs without his permission. We didn't know what happened to his two friends who joined him at the start.

It took a lot of planning to escape from that place. I left all my family and our belongings and was the only one in the family to survive.

Communism is a concept that looks very attractive at the beginning until it eats you off completely. Once you are gullible enough to let that idea enter your door, you will ruin everything you cherish.


This story is loosely based on the Nobel winning work of Doctor Zhivago (novel) and among the greatest novels of all time Animal Farm, along with the biographies of Joseph Stalin and Vladmir Lenin.

As an aside, don't give a 10 year old easy answers on such tough questions. Simple answer will most likely be wrong. Pique their interest and help them ask the right questions.

How can Communism be explained to a ten year old?

What is the A – Z of web development and web design?

What is the A – Z of web development and web design? by @ossia

Answer by Quincy Larson:





















Users =






I only write about programming and technology. If you follow me I won’t waste your time.

What is the A – Z of web development and web design?