Tag Archives: quora

How close does an object have to be to earth to be pulled by gravity?

Pulled from Quora, here is one of the best, and most popular, answers to a question. Written by Mark Eichenlaub, a graduate student in physics.

How close does an object have to be to earth to be pulled by gravity?

This question doesn’t have a direct answer because, for lack of a less-direct way of saying it, that’s not the way it works. If there were no atmosphere, you could have the ISS be just above the surface of the Earth, high enough only to clear the mountains. On the other hand, you could have something as far out as the moon, and if it weren’t going fast enough and in the right direction, it would still fall back down. The ISS doesn’t stay up because of how high it is, but because of a combination of that and how fast it’s going.

One of the most difficult things to learn about physics is the concept of force. A force in a given direction does not make things go straight in that direction. Instead, it influences the motion to be a bit more in the direction of the force than it was before.

For example, if you roll a bowling ball straight down a lane, then run up beside it and kick it towards the gutter, you apply a force towards the gutter, but the ball doesn’t go straight into the gutter. Instead it keeps going down the lane, but picks up a little bit of diagonal motion as well.

Now we can talk about an very early thought experiment in physics. Imagine you’re standing at the edge of a cliff 100m tall. If you drop a rock off, it will fall straight down. If you throw the rock out horizontally, it will fall down, but it will keep moving out horizontally as it does so, and falls at an angle. (The angle isn’t constant – the shape is a curve called a parabola, but that’s relatively unimportant here.)

The the force is straight down, but that force doesn’t stop the rock from moving horizontally. If you throw the rock horizontally harder, it goes further, and falls at a shallower angle. The force on it is the same, but the original velocity was much bigger and so the deflection is less.

Now imagine throwing the rock so hard it travels one kilometer horizontally before it hits the ground. If you do that, something slightly new happens. The rock still falls, but it has to fall more than just 100m before it hits the ground. The reason is that the Earth is curved, and so as the rock traveled out that kilometer, the Earth was actually curving away underneath of it. In one kilometer, it turns out the Earth curves away by about 10 centimeters – a small difference, but a real one.

As you throw the rock even harder than that, the curving away of the Earth underneath becomes more significant. If you could throw the rock 10 kilometers, the Earth would now curve away by 10 meters, and for a 100 km throw the Earth curves away by an entire kilometer. Now the stone has to fall a very long way down compared to the 100m cliff it was dropped from. Continue reading

Why Facebook bought Instagram – from Om Malik and Robert Scoble

Both Om Malik and Robert Scoble make interesting points, Facebook paid double for what many considered Instagram to be worth and Facebook desperately needs help with mobile devices.

From Om Malik:

A few days ago Instagram was rumored to be valued at $500 million. A few months ago it was $300 million. Its last round — just a year ago – valued the company at $100 million.

The rising valuation of the company was reflective of the growing audience it has been garnering, despite being just on the iPhone. It had reached nearly 30 million registered users before it launched an Android app.

So the question is:  Why did Mark Zuckerberg buy Instagram at twice the valuation that professional venture investors were putting on it?

From Zuckerberg’s post on Facebook:

This is an important milestone for Facebook because it’s the first time we’ve ever acquired a product and company with so many users. We don’t plan on doing many more of these, if any at all. But providing the best photo sharing experience is one reason why so many people love Facebook and we knew it would be worth bringing these two companies together.

My translation: Facebook was scared shitless and knew that for first time in its life it arguably had a competitor that could not only eat its lunch, but also destroy its future prospects. Why? Because Facebook is essentially about photos, and Instagram had found and attacked Facebook’s achilles heel — mobile photo sharing.

 

From Robert Scoble:

Facebook has a problem. After its IPO completes it needs many quarters of strong revenue and profit growth to report to convince investors to stay put and convince new ones to buy the stock.

Zuckerberg is aiming at turning the $80 to $100 billion valuation that will happen at IPO into a $500 billion to $1 trillion company. How will he do that?

Look at mobile.

Today Facebook has NO revenues from mobile. None. That’s amazing, since so many people, hundreds of millions of us, use Facebook on mobile clients.

That will change very quickly after the IPO. Instagram will play a huge role here, plus Facebook gets a very talented mobile development team that has built world-leading mobile apps on iOS and Android (which got a million users in its first day).

Is Craigslist is done for? (nope)

This is part 2 and it messes everything up.

Part 1 was incredibly convincing and most of us bought the argument, hook-line and sinker.

We were ready to write-off Craigslist.

Now, I present the counter-argument. This piece will completely change your mind. It will challenge you to re-think everything and in my case, put Craigslist back on the map for good.

Enjoy.

PS – It works better if you read the original piece first: Is Craigslist done for? (yep)

From Quora

Josh Hannah argues that the premise of this question is false and that Craigslist “has been disrupted.” He mistakenly confuses “competition” with “disruption.”

Craigslist has not been disrupted.

Disruption means to “drastically alter or destroy the structure of (something).” By definition this means that disruption is easy to spot. Something new comes along and crushes an existing business model or technology or product.

Here are a few examples:

Business model disruption:

  • Craigslist disrupted classified advertising
  • CPA disrupted CPM
  • Free has disrupted numerous other industries (telecom, media, etc)

Technology disruption:

  • Cars disrupted horses
  • Downloadable media disrupted CD’s & DVD’s
  • Digital photography disrupted film

Product disruption:

  • Facebook disrupted MySpace
  • Google disrupted AltaVista & co

In every case:

  • The disruption happened suddenly (within a few years)
  • The disruptor’s value proposition was unambiguous
  • Usually a single replacement (business model, tech, product) filled the void

This is what disruption looks like with websites:

This is what disruption looks with offline businesses:

This is not disruption:

…Nor is this:

Josh argues that:

“Bad sites with network effects show much slower decay in use than they should based on their absolute quality. (think eBay.) Bad sites who price most of their product at free show incredibly slow decay in use. (think Craigslist).”

All of this is true, but this is precisely why Craigslist is not being disrupted: It already benefits from enormous network effects, which aren’t being replicated by its myriad competitors. Even if all the sites below shared the same audience as Craigslist (they’re not even close), these users would be split across 30 different sites:


Yes, plenty of people are picking apart categories and trying to improve upon the product, the UI, or the way the information is presented. This has been happening for years and many of these companies have gone under. If you think about it, these companies aren’t really competing directly with Craigslist because Craigslist–unlike every site above–is free.

To argue the image above is indicative of disruption is to misunderstand why Craigslist is successful. How many companies compete with Google in search, advertising, social, apps, mobile? Sheer volume of competition does not signal disruption.As I wrote previously, Craigslist benefits from a killer product/business model combo that protects it from the effects of these startups:

Craigslist = Simple + Free + Network effects + Anonymous

It’s very, very hard to compete with something that gets the job done well enough and is free.

People can criticize the product/UI/search all day long, but minor tweaking is not going to disrupt Craigslist–particularly if it happens across 30+ fragmented sites. Most people have a status quo bias…they must see substantial and compelling benefits to changing their behavior. They won’t learn about all the sites listed above just so they can get a slight UI improvement when they want to unload their couch or casually rent a hooker. (Frequent escort renters might disagree with me :).

Even if someone rolled all 30 of these sites into one competitor with better features, UI, search, etc it’s still unlikely to succeed because of the power of network effects. Craigslist has them. The other guy don’t. And no one can afford to buy these network effects unless they plan to charge for their services. And if they plan to charge then they’re back to square one.

In summary (and forgive me for mashing these answers together):

This is a winner take all business that’s supported by incredible network effects, great brand equity, a degree of trust and familiarity. No upstart is going to unseat Craigslist without a huge & foolish capital investment. The only way Craigslist will be disrupted is if consumer behavior shifts radically away from free, online, and anonymous.

Is Craigslist is done for? (yep)

This is part 1 of 2 which proves that Craigslist is already dead, or in the midst of a slow death.

From Quora

Craiglist has been disrupted, it’s just not obvious yet. And the world will be a better place for it.

Craigslist has fewer unique visitors today than it did at this time in 2009.

Bad sites with network effects show much slower decay in use than they should based on their absolute quality. (think eBay.) Bad sites who price most of their product at free show incredibly slow decay in use. (think Craigslist). But make no mistake, it is happening.

The evidence of their poor quality is so obvious it’s hardly worth stating. Suffice it to say, if I’m looking to rent an apartment, it would be nice not to see the same listing reposted every day, and having to re-read it and figure out if I’ve called them before. It might be even nicer to view them on a map, or god forbid have new and relevant listing emailed to me.

Sites like Oodle have tried to take it head on with a superior interface but have been unable to displace them. Sites like Kijiji have been launched by eBay, or OLX, which is distributed on other people’s platforms with large traffic, have tried to leverage other sources of traffic to combat the critical mass.

Generally speaking, Craigslist has been “good enough” to not be disrupted head-on. Nevertheless, the world moves on, and the gaps in their product (due to a stubborn obstinate refusal to invest in technology) grow wider and wider. As tablets, smartphones, etc disrupt, and craigslist doesn’t invest in those platforms, the feature gap grows wider.

The disruption that has happened has occurred on a category-by-category bases, as this graphic by Andrew Parker (http://thegongshow.tumblr.com/po…) shows:

StubhubAirbnbEtsy have built big businesses in some of these categories, and floods of new startups try to pry off pieces (TaskRabbit, many others).

I have derived a lot of utility out of Craigslist over the years, and it has all come free, so I am grateful for that. But the site reportedly pulls in more than $100M in revenue a year (What is Craigslist’s revenue?) , has only a few dozen employees, continually under-invests in technology and does not innovate. I don’t think Craig’s a bad guy, but he’s harvesting $50M a year into his pockets and not improving the site. In ten years I think Craigslist will be an afterthought, whereas if he reinvested half of those profits into technology and product, it would have a real shot to be a category leader.

Update: Do you think Craigslist is done for….if so Part 2 is now available and it will change your mind – Is Craigslist done for? (nope)

You can reuse all new content on Quora

Quora is a fantastic resource for and I often want to share the info I find. With that in mind I found the following copyright rules on the site:

This is an official Quora policy that reflects the agreed upon conventions of the community

You can reuse all new content on Quora by publishing it anywhere on the web, as long as you link back to the original content on Quora. There are some more details to this specified at http://www.quora.com/about/tos. We wrote this with the interests of contributors in mind:

Subject to these Terms, Quora gives you a worldwide, royalty-free, non-assignable and non-exclusive license to re-post any of the Content on Quora anywhere on the rest of the web provided that the Content was added to the Service after April 22, 2010, and provided that the user who created the content has not explicitly marked the content as not for reproduction, and provided that you: (a) do not modify the Content; (b) attribute Quora with a human and machine-followable link (an A tag) linking back to the page displaying the original source of the content on quora.com; (c) upon request, either by Quora or a user, remove the user’s name from Content which the user has subsequently made anonymous; (d) upon request, either by Quora or by a user who contributed to the Content, make a reasonable effort to update a particular piece of Content to the latest version on quora.com; and (e) upon request, either by Quora or by a user who contributed to the Content, make a reasonable attempt to delete Content that has been deleted on quora.com.

Pretty cool.

I also learned that there is a feature authors can use if they want to keep their answers from being published elswhere:

Not for reproduction. The “Not for reproduction” option opts a user’s answer out of the normal reuse license that Quora grants to everyone. If you’re posting about an NFR answer there is not a restriction. However, if you’re copying the contents of an NFR answer to somewhere else on Quora or to anywhere else on the web, the author of the answer might be able to stop you under copyright law, depending on whether your use qualifies as fair use. We don’t police this; it’s the same as if you wrote a blog post that included the contents of someone else’s blog post.

How could Apple spend its $51 billion cash?

The common advice would be to acquire some hot property like Twitter, Pandora, or Hulu. Doing so would satisfy Wall Street’s insatiable hunger for greedy growth, but wouldn’t be all that strategic.

Another idea would be for Apple to invest in itself. A post over on Business Insider highlights this using a thread on Quora.

It started with this question, “What would make sense for Apple to use its $51+ billion in cash for a strategic acquisition?”

The two most interesting answers present inspired analysis of the company.

One has a list of Apple acquisitions since 1997 and points out that all have been small, with most in the $10-20 million range. The biggest on record was over a decade ago with the “purchase of NeXT that brought Steve Jobs back to Apple”.

1997 Next (programming services). Value: $404 million
1997 Power Computing (cloned computers). $100 million
1999 Xemplar Education (software). $5 million
1999 Raycer Graphics (graphic chips). $15 million
2000 NetSelector (Internet software). Value: NA
2001 Astarte (DVD authoring software). Value: NA
2001 bluebuzz (Internet service provider). Value: NA
2001 Source Technologies (graphics software). Value: NA
2001 PowerSchool (online info systems services). $62 million
2002 Nothing Real (special effects software). $15 million
2002 Zayante (software). $13 million
2002 Silicon Grail Corp-Chalice (digital effects software). Value: NA
2002 Emagic (music production software). $30 million
2002 Propel Software (software). Value: NA
2005 Fingerworks (gesture recognition). Value: NA
2006 Silicon Color (software). Value: NA
2006 Proximity (software). Value: NA
2008 P.A. Semi (semiconductors). $268 million
2009 Placebase (maps). Value: NA
2009 Lala (music streaming). $17 million
2010 Quattro (mobile advertising). $275 million
2010 Intrinsity (semiconductors). $121 million
2010 Siri (software). Value: NA
2010 Poly9 (Web-based mapping). Value: NA

The second, even more insightful, points out that the majority of Apple’s cash is used for strategic capital investment. They find a new technology they want in on and buy the factory, patent, or supply chain and then secure exclusive contracts for them.

Even writing in first-purchase clauses, where they get exclusive production discounts by fronting some start-up costs for the new factories.

Read the full answer for more details on how this world-class supply chain operates:

Apple actually uses its cash hoard in a very interesting way to maintain a decisive advantage over its rivals:

When new component technologies (touchscreens, chips, LED displays) first come out, they are very expensive to produce, and building a factory that can produce them in mass quantities is even more expensive. Oftentimes, the upfront capital expenditure can be so huge and the margins are small enough (and shrink over time as the component is rapidly commoditized) that the companies who would build these factories cannot raise sufficient investment capital to cover the costs.

What Apple does is use its cash hoard to pay for the construction cost (or a significant fraction of it) of the factory in exchange for exclusive rights to the output production of the factory for a set period of time (maybe 6 – 36 months), and then for a discounted rate afterwards. This yields two advantages:

  1. Apple has access to new component technology months or years before its rivals. This allows it to release groundbreaking products that are actuallyimpossible to duplicate. Remember how for up to a year or so after the introduction of the iPhone, none of the would-be iPhone clones could even get a capacitive touchscreen to work as well as the iPhone’s? It wasn’t just the software – Apple simply has access to new components earlier, before anyone else in the world can gain access to it in mass quantities to make a consumer device. One extraordinary example of this is the aluminum machining technology used to make Apple’s laptops – this remains a trade secret that Apple continues to have exclusive access to and allows them to make laptops with (for now) unsurpassed strength and lightness.
  2. Eventually its competitors catch up in component production technology, but by then Apple has their arrangement in place whereby it can source those parts at a lower cost due to the discounted rate they have negotiated with the (now) most-experienced and skilled provider of those parts – who has probably also brought his production costs down too. This discount is also potentiallysubsidized by its competitors buying those same parts from that provider – the part is now commoditized so the factory is allowed to produce them for all buyers, but Apple gets special pricing.

Apple is not just crushing its rivals through superiority in design, Steve Jobs’s deep experience in hardware mass production (early Apple, NeXT) has been brought to bear in creating an unrivaled exclusive supply chain of advanced technology literally years ahead of anyone else on the planet. If it feels like new Apple products appear futuristic, it is because Apple really is sending back technology from the future.

Once those technologies (or more accurately, their mass production techniques) become sufficiently commoditized, Apple is then able to compete effectively on cost and undercut rivals. It’s a myth that Apple only makes premium products – it makes them all right, but that is because they are literally more advanced than anything else (i.e. the price premium is not just for design), and once the product line is no longer premium, they are produced more cheaply than competitor equivalents, yielding higher margins, more cash, which results in more ability to continue the cycle.

Here is one of those famous Apple production videos which highlights the aluminium machining technology.