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How to Easily Locate the Accelerometer in an iPhone

Everyone should probably know that I’m obsessed with both physics and smart phones. If I can use my phone for a physics experiment, I’m good to go. That’s exactly what I am going to do right now—use some physics to find the location of the accelerometer in the iPhone 7.

Your smart phone has a bunch of sensors in it. One of the most common is the accelerometer. It’s basically a super tiny mass connected with springs (not actual springs). When the phone accelerates in a particular direction, some of these springs will get compressed in order to make the tiny test mass also accelerate. The accelerometer measures this spring compression and uses that to determine the acceleration of the phone. With that, it will know if it is facing up or down. It also can estimate how far you move and use this along with the camera to find out where real world objects are, using ARKit.

So, we know there is a sensor in the phone—but where is it located? I’m not going to take apart my phone; everyone knows I’ll never get it back together after that. Instead, I will find out the location by moving the phone in a circular path. Yes, moving in a circle is a type of acceleration.

Of course you already knew that circular motion was a type of acceleration. Yes, you knew this because you have been in car (you have probably been in a car). It turns out that the human body can also feel accelerations—although we sometimes confuse these accelerations with gravitational forces, but we can still feel them. If you are sitting in a car seat and the vehicle speeds up, it accelerates and you can feel that. Now if that car is turning in a circle, you can also feel it. That turning car is accelerating—even if it travels at a constant speed.

If you want to really understand why circular motion is a type of acceleration, you need to start with the definition of acceleration.

Here the Δ means “change in”. So the acceleration is the change in velocity divided by the change in time—that is a rate. But here is the key point. Both the acceleration and velocity are vector quantities. This means that they depend on direction as well as magnitude. Since the velocity is a vector, you can have an acceleration just by changing the direction of the velocity. Moving in a circle at a constant speed means there is indeed an acceleration.

If we have an object moving in a circle, the acceleration is pointed towards the center of the circle and depends on two things: the angular velocity (ω) and the circular radius (r). If you increase either of these values, the magnitude of the acceleration will also increase according to the following:

So perhaps you can see where this is going. If I move a phone around in a circle, I can measure both the acceleration and the angular velocity. From this, I can calculate the radius of the circle—which will be the distance from the center of the circle to the accelerometer. That shouldn’t be too difficult. Actually, I have done this experiment before but it was a slightly different setup.

Actually, you can do this yourself. Really, all you need a device that rotates the phone such that it moves in a circle with a constant radius. For me, I used this nice rotating platform.

Notice the addition of the ruler so that I can accurately measure the distance from the center of the circle to the bottom of the phone. I also put a small clamp at the end to prevent the phone from flinging off the platform. That would be bad.

The other thing you need is a way to measure both the angular velocity and the acceleration. Most phones have a type of gyroscope to measure rotations so that you can get both measurements with your phone. Although there are several apps to record sensor data on your phone, but I really like PhyPhox (for both Android and iOS).

Now we are all set. Start recording data and rotate the phone. As the angular velocity changes, so does the acceleration (since the radius is fixed). Since the acceleration is proportional to the square of the angular velocity, I can plot acceleration vs. ω22. It should look something like this (hopefully).

It seems to be linear—so that’s good. The slope of this line is 0.14138 meters with an intercept of 0.093 (rad/s)2 (that’s close to zero). That slope is the important part. It’s the distance from the center of the circle to the sensor. I recorded the distance of the bottom of the phone to the center with a radius of 0.09 meters. This means that the accelerometer is 5.1 centimeters above the bottom of the phone.

But wait! What about the side-to-side location? I can repeat the experiment with the side of the phone facing the center of the circle. Here is the data for that run.

In this case, I had the screen facing down with the “sleep” button side of the phone facing the center of the circle at a radius of 15.9 cm. The slope of the line above is 17.7 cm. That means the sensor is 1.8 cm from the side. OK, this is technically wrong, but I’m going to use it anyway. The 17.7 cm is actually the radial distance to the sensor. This will only give me the distance from the side of phone if the sensor was half way from the top of the phone. Oh well, this will be close enough.

So here is a diagram of my iPhone (looking at it from the back).

Pretty sure that’s where the sensor is located. Now I just need to take apart my phone to verify this result. Oh wait. I’m not going to do that.

Read More On This At Science Latest

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10 robotic dogs pull truck along in new video

Image Credit: YouTube / Boston Dynamics

The robots seemed to have no problem hauling the truck.

A small army of Boston Dynamics’ dog-like robots have been filmed hauling a truck through a parking lot.

Known as SpotMini, this four-legged contraption has become something of a celebrity in recent years thanks to videos showing it performing a wide range of tasks and balancing acts.

This latest footage shows more of the robots than ever before – ten of them to be exact – all working together to haul a large truck through the parking lot outside Boston Dynamics’ headquarters.

Each robot is 0.84 meters tall and can carry a payload of around 14kg.

What’s interesting is that these robots will actually be available for companies to purchase in the near future, meaning that they are no longer just a work-in-progress.

“It only takes 10 Spotpower (SP) to haul a truck across the Boston Dynamics parking lot,” the firm wrote in the caption for the video on YouTube.

“These Spot robots are coming off the production line now and will be available for a range of applications soon.”

Source: Evening Standard

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New CRISPR Tech Could Cure Herpes

Hunter-Seeker

Gene hacking techniques that were recently used in human cells for the first time could someday let doctors shred up and destroy viruses like herpes or hepatitis B inside human cells, scientists say.

The new technique is called CRISPR-Cas3 — usually, when you hear about CRISPR tech, it’s the Cas9 variety — and Cornell researchers believe it could be used to cure viral diseases, according to a university-published press release.

DNA Shredder

The scientists used Cas3 to identify and shred long stretches of human DNA, according to research published in the journal Molecular Cell last week. The new gene-hacking tool makes more and broader cuts in genetic material than CRISPR-Cas9, meaning it could let scientists quickly learn what specific, long stretches of genetic information do and how they interact with certain diseases.

It also means that the gene-hacking tool could attack and shred viral DNA.

“My lab spent the past ten years figuring out how CRISPR-Cas3 works. I am thrilled that my colleagues and I finally demonstrated its genome editing activity in human cells,” said Cornell molecular biologist Ailong Ke. “Our tools can be made to target these viruses very specifically and then erase them very efficiently. In theory, it could provide a cure for these viral diseases.”

READ MORE: CRISPR-Cas3 innovation holds promise for disease cures, advancing science [Cornell Chronicle]

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Scientists Put Human Brain Genes in Monkeys and Made Them Smarter

It’s time for the latest edition of “What Could Possibly Go Wrong?”, the game show that pits seemingly unethical science against potentially catastrophic predictions. In today’s competition, scientists in China (one point already for the catastrophic team) announce they used gene-editing to place human brain genes in rhesus macaque monkeys and it made their brains smarter. Cue the music from every “Planet of the Apes” movie and let the game begin!

“The presented data represents the first attempt to experimentally interrogate the genetic basis of human brain origin using a transgenic monkey model, and it values the use of nonhuman primates in understanding human unique traits.”

If the opening paragraph of the new study, “Transgenic rhesus monkeys carrying the human MCPH1 gene copies show human-like neoteny of brain development,” published recently in the journal National Science Review, is any indication, scientists are learning from lawyers how to protect their clients/experiments by hiding them in clouds of big, confusing words and phrases. Experimentally interrogate?

This is interesting.

China Daily reports that researchers from the Beijing-based National Science Review, the Kunming Institute of Zoology, Chinese Academy of Sciences and the University of North Carolina (that’s in the U.S. – looks like it’s playing for the Seemingly Unethicals) edited human MCPH1 genes – a gene that is critical in fetal brain development because it controls brain size and rate of growth – and created 11 transgenic (a cloud word meaning “artificially carrying DNA from an unrelated organism”) monkeys. Eight of those monkeys were first-generation and three were second-generation, obliterating the ‘artificial’ part of ‘transgenic’ by getting their human genes from their monkey parents.

“According to the research article, brain imaging and tissue section analysis showed an altered pattern of neuron differentiation and a delayed maturation of the neural system, which is similar to the developmental delay (neoteny) in humans.”

In other words, the monkeys showed the human trait of slow brain development (neoteny) rather than the rapid growth of normal monkey brains. What was the benefit of this slow growth?

“The study also found that the transgenic monkeys exhibited better short-term memory and shorter reaction time compared to wild rhesus monkeys in the control group.”

To put it bluntly — even the monkeys could understand the results because the human genes made them smarter!

Ding-ding-ding! That bell means it’s time to play the lightning “What could possibly go wrong?” round.

Time-out called by the Potentially Catastrophics. In a shocking and somewhat honorable display of conscience, Martin Styner, a University of North Carolina computer scientist and coauthor of the Chinese report, told the MIT Technology Review that his role was merely to train Chinese student on how to extract brain volume data from MRI images and, after learning the true purpose, considered removing his name from the paper, which he claims could not find a publisher in the West. Styner then throws his “What could possibly go wrong?” pitch:

“I don’t think that is a good direction. Now we have created this animal which is different than it is supposed to be. When we do experiments, we have to have a good understanding of what we are trying to learn, to help society, and that is not the case here.”

Is this going to be a sequel to Planet of the Apes or Flowers for Algernon?

Unfortunately, that pitch didn’t strike out Bing Su, the geneticist at the Kunming Institute of Zoology who led the research. He told the MIT Technology Review he is planning to create more smart monkeys and is planning to test another gene — SRGAP2C – which has been called the “humanity switch” and the “missing genetic link” because it appeared about two million years ago when Australopithecus (the Southern Ape) was being replaced by the smarter Homo habilis.

Putting the “humanity switch” in a monkey? What could possibly go wrong? This game isn’t over … it’s barely starting. Is this progress … or an unethical march down the field to unforeseen consequences?

If we’ve learned anything from “Planet of the Apes,” it’s that if this game goes into overtime, it won’t be a sudden death.

Source: Mysterious Universe

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