Perhaps we should have read it as an omen that the MagSafe 2 arranger for elder , original MagSafe connexion was listed as discontinued on the Apple Store in the U.S. and Canada last week . It’sback in stockthis week , but MagSafe ’s time to come in new Mac laptops is changeable with the revelation of thesingle - port MacBook . With just a USB - C connection for index , data , and exhibit , MagSafe may be on its mode to sing with the choir invisible .
That ’s a shame because Apple has retrain mass of all long time , and perhaps some animals , to not occupy about Mac laptop world power cables . Go in front ! Stand on it , tripper over it , yank it — the force of the smallest effort pulls it free .
To quoteApple ’s MagSafe patent :
… the surface country of two magnetically draw half determines the number of magnetic magnetic flux lines and therefore the holding force between them because the guard force is proportional to the contact area between the two magnetically pull halves …
What they said .
A USB Type C ( or USB - C ) cable has no such advantage . It has two clear-cut conflict : first , a USB - ascorbic acid male person end , such as the tip of a cable , is plugged into a interface , very much wish big and deeper Type A and Type B USB joining .
secondly , while MagSafe was optimized to help with “ non - axile ” force — any guidance except straight out — the USB - C panache cud and jackfruit get the worst from that . As astrophysicistKatie Macksaid , “ The maven of the MagSafe connecter is that if you practice a force inany other directionit unwrap the magnetised seal very easily , and then there ’s virtually no force ask to slay the connective all . ”
MagSafe ( right ) and MagSafe 2 ( left ) are n’t as versatile as USB - C , but they ’ve pull through our bacon so many fourth dimension .
But how probable is a corduroy - tripper to yank a Modern MacBook off a surface versus the USB - C cable length coming out first ? My deliberation , vetted by Mack and a diverseness of engineer , show it ’s almost certain the MacBook will move a bit or a draw unless all your star dead align .
have got on ! Some mathematics ’s amount , but it ’s deserving it .
There’s a disturbance in the force
The USB Implementors Forumspecifiesprecisely how much military group should be required to pull a USB - C cable television costless , measured in newtons ( N ) , which is the force required to accelerate one kg ( kg ) of hoi polloi at 1 meter per second squared ( 1m / s2 ) . Because an target under acceleration continuously increases its velocity , an object travelling at relief that is moved at 1m / s2traverses 0.5 m ( 1.6 foot ) in the first 2d , 2 K by the second second , and 4.5 m by the third second .
The USB group say a fresh connector should call for 8N to 20N of origin force . After 10,000 connection oscillation , no few than 6N should be expect . ( To compare with something you ’re already familiar with , USB Type A connexion sold as parts typically notice a minimum 10N forcefulness for extraction . )
The MacBook exerts a pull of its own , just sitting there . We set out with its lot , 2.03 lbs ( 0.92 kilogram ) , which would want a force of about 0.9N to speed up it to 1m / s2 . But we also have gravity in our world , and a so - called normal personnel must be forecast . countenance ’s assume the MacBook is on a layer open . The earthly concern exercise a pull of close to 10m / s2at the surface . We procreate that by 0.92 kg to get our force in newtons , or approximately 9N. ( Aerospace engineerBradley Grzesiakcautioned me to avert too many decimal lieu : earth ’s gravity varies enough around the orb . )
The new MacBook has rubber foot on the bottom , just like the current Apple laptop . But it ’s also lighter , which think it claim less power to move it .
But we have to factor out in detrition . take for granted the rubber - footed MacBook — it has four feet , just like a MacBook Air — is on a woodwind table . A standard friction coefficient for rubber on forest , the close comparison I could recover , is 0.70 for unchanging rubbing ( sometimes called stiction ) , or friction at a standstill . Dr. Drang — the nom de Internet of a consulting engineer who write exceedingly clever thing about scientific discipline , package , and technology — propose via electronic mail that 0.70 is affirmative for many surfaces , and 0.40 more fair .
Now we multiply the coefficient of 0.70 to get roughly 6N , or 0.40 to get about 4N. If the laptop is on a slick alloy or chalk table , the coefficient could be 0.20 , or 2N or so . regard gravity : this range of 2N to 6N is about 20 to 60 percent of one earthly concern solemnity . Not so much !
However , Grzesiak pointed me to a 1942 National Bureau of Standards ( now NIST)testing report on rubber(see above ) that looked with more particular into the initial gunpoint of whelm inactive rubbing at various rate of initial acceleration . The higher the acceleration from zero velocity , the larger the coefficient .
You want to get nerdy about the frictional prop of rubber ? Oh , we can get nerdy about the frictional place of gum elastic .
A saccade from a cable’s length could accelerate a laptop computer so quickly that the initial coefficient factor of rubber eraser on a glass table could be as gamey as 5 — meaning you ’d want force play on the order of five earth gravitational force ( 50N ) to get the MacBook moving . But think that force involves flock and quickening : an abrupt yank by a heavy weight unit ( like a human ’s pegleg intersecting with a cable ) could briefly produce violence on that order of magnitude of order of magnitude !
After the laptop computer has overcome static rubbing , energising clash comes into play , dramatically decoct the effect necessary to keep it in motion and speed it further .
A smashing good outcome
We have a wad of idealized and estimated starting conditions , so we can execute our thought experiment now . ( I ask Apple for input signal , but did n’t hear back . )
get ’s take the case in which someone perform the most thoroughgoing pratfall such that the direction of force is absolutely and perfectly opposite the USB - snow gob , so that there is no shear in any other orientation that we call for to consider .
In that scenario , we know you ask to apply an initial military group of between 2N and 50N depending on textile and presumptuousness to cause the MacBook to reach an acceleration charge per unit of the charming 1m / s2 , but then less force thereafter . Since we need to pull out at 8N to 20N to remove the connector , this is clear ambiguous . Will the plug have rend out of the Jack-tar by the time static friction has been subdue ?
Click to exposit .
And there ’s a wrinkle . If you acceleratefaster , you practise cracking force . That is , take 1 kg to 2m / s2 , and the military group is 2N. Thus , take the action at law note above of someone ’s leg intersecting with the cable , and take on the mass of the wooden leg involved in the force is 10 kg . That ’s a tenfold multiplier against any acceleration produced .
The cable’s length ’s tip and socket are supposed to measure just 6 mm . Assuming the USB origin force ’s upper end , 20N , is the stable friction and 8N is the kinetic friction , it ’s potential that the cable television service pops free in a fraction of a 2nd before the laptop computer affect much , if at all .
Dr. Drang explained to me further :
What materialise to the MacBook when you pull on the cable has less to do with the force you apply than the rapidity with which you practice it . If you pull on the line with constant speed , or with any acceleration less than 4.8 m / s2 , the connexion will never descend out , and you ’ll underprice the MacBook on the floor . If you pull on the cable with an acceleration greater than 17.8 molarity / s2 , the connector will descend out and you ’ll heave a sigh of relief .
Because the USB Implementors Forum trace a broad range in the spec , until and if Apple ’s specific USB - C adapter is tested across multiple computing machine for extraction force out , it ’s impossible to hump the necessary acceleration .
get ’s also calculate at cases with shear , where the cord is tripped over or jerk at any angle or orientation . Mack noted , “ pull out the cable cleanly would be very unmanageable to do by stroke . If you ’re pulling at any angle other than straight on , it ’s quite difficult , as the violence is now lead in a charge that would increase friction a destiny . ”
Dr. Drang and Mack both said that if the laptop was spare enough to be dragged off a aerofoil , that shear could be reduced by the laptop turn out first to a less oblique horizontal slant . However , there ’s still the affair of the angle from the MacBook to the point on the cablegram where force is being applied . That ’s likely vertical , a drop from the wad ’s slot to the floor where someone ’s understructure or leg catches on the cable .
Greg Koenig , an industrial designer in Portland , Oregon , and a principal atLuma Labs , examined Apple ’s logic gameboard image and other picture of the MacBook at my request . He noted that the USB - C distaff connecter is n’t part of the primary system of logic table , unlike connection on late MacBooks . This isolate legal injury , if any were to occur .
The new MacBook ’s logic board does n’t run to the edges of the subject , so if the USB - light speed porthole hold up legal injury , the rest of your MacBook could be unaffected . Assuming it has n’t crash to the base .
Koenig tell the porthole ’s figure does n’t expose any portion of the sheet alloy beyond the aluminum case . With enough devious force , the cablegram ’s metal head will be pinion against the MacBook ’s frame , not order stress instantly on the port . If the laptop is loose on a surface , get out obliquely on the cable will almost certainly bring the laptop with it more faithfully than in our “ perfectly straight - out ” thought experiment .
However , if the laptop is secured in some fashion — even if you ’re control it tightly in your hands — the cablegram ’s male sparking plug final stage is probably the weak full stop , and it would be tear off , said Koenig , leaving its case in the USB - C port , potentially without causing any harm to the MacBook . The metal racing shell could then be remove cautiously .
Trip the lightweight fantastic
At some level , I ’m trying to overturn engineer Apple ’s thinking around design and testing , both in its larger engineering science participation in mould USB - C , and in its particular carrying out . All the reckoning and exercises above have for sure been performed a thousand clip in simulation and prototyping internally , shaping the growing of the socket , logic board , outside cables , and more .
In the terminal , it ’s not really enough . mack laptop computer are die to go gate-crash to the priming coat in vastly greater quantities than they have over the last several years . I ’ve heard it say since Monday morning that MagSafe was the single best computer hardware feature article Apple invented for its laptop computer , and I ’m hard press out to deny that — although redundant - long battery life is overnice , too .
Clearly , MagSafe was good and experts agree . I advocate retrain your toddlers now .
( Thanks also toRamez Naamfor schooling me in some of the purgative and spitballing mind . )
