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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.

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Aliens & UFO's

Ecto-1 Returns in Teaser for Secret Ghostbusters Movie

Trailer teases the return of the Ghostbusters with a malfunctioning proton pack and a rusting Ecto-1.

A new Ghostbusters is coming in 2020! It was announced this week with the arrival of this short but effective teaser trailer. It’s an eerie night and spine-tingling music from the original Ghostbusters score is playing as the camera moves past a fence dripping with ectoplasm into an creepy barn where we hear the sound of proton pack that won’t start. And then the wind blows up a tarp to reveal a rusting Ecto-1.

The new film is being directed and co-written by Jason Reitman, the son of Ivan Reitman who directed the original Ghostbusters.

“I’ve always thought of myself as the first Ghostbusters fan, when I was a 6-year-old visiting the set. I wanted to make a movie for all the other fans,” Reitman told Entertainment Weekly. “This is the next chapter in the original franchise. It is not a reboot. What happened in the ’80s happened in the ’80s, and this is set in the present day.”

A rusting Ecto-1 from the Ghostbusters teaser trailer

For those of us who grew up in the 80s, the 1984 Ghostbusters film was probably one of our earliest introductions to the occult, inspiring a lifetime of obsession. Sure, I was disappointed when I learned Tobin’s Spirit Guide wasn’t real, but my hope was renewed when I discovered real occult texts. And of course Ecto-1, a 1959 Cadillac built by the Miller-Meteor company, kick-started a love for hearses.

Do you believe in UFOs, astral projections, mental telepathy, ESP, clairvoyance, spirit photography, telekinetic movement, full trance mediums, the Loch Ness monster and the theory of Atlantis?

I probably had not even heard of these things before Ghostbusters.

The new Ghostbusters is set for a 2020 release.

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Science & Technology

A New Class of Drugs Could Make Safer Sleeping Pills

ZZZ

If your house caught fire in the middle of the night, you’d want to wake up to deal with that emergency, right?

In a new prescription sleeping pill study published this week in Frontiers in Behavioral Neuroscience, half of the study participants slept through a fire alarm as loud as someone vacuuming next to their bed. Researchers from Kagoshima University, Japan estimated that millions of people taking prescription sleeping pills like Ambien and Halcion would sleep through a fire alarm. They propose that a new class of hypnotic drug might be used as an alternative which would function like a sleeping pill while still allowing the brain to wake up during an emergency.

DORA The Hypnotic Drug

The most widely prescribed type of sleeping pills, benzodiazepines, are really effective at getting the brain into “sleep mode”. Unfortunately, they act as a sort of blanket, suppressing areas of the brain that they don’t need to. That includes the area of the brain that decides which external information, such as noises in the night, to pay attention to.

Over the past decade scientists have been developing a new class of hypnotic drugs called dual orexin receptor antagonists (DORAs). DORAs more selectively target the brain’s sleep/wake pathways making them a safer alternative to benzodiazepines while also leaving the user with a reduced hangover-like affect these drugs can cause.

Wake-up Call

When tested in lab mice, those that had been given the benzodiazepine triazolam were slower to rouse than those given DORA-22 when presented with the sounds of a fox, a serious threat to a mouse. Better still, once the danger had passed the mice given DORA-22 fell back asleep as fast as the mice that had been given a sleeping pill, and significantly faster than mice that hadn’t been given anything at all.

More human testing is needed in order to show DORAs have potential applications as sleep aids. Since 2014, a DORA called surovexant has gained regulatory approval in Japan, the USA and Australia. High costs and limited clinical testing of surovexant have stymied its use but new types of DORAs currently in development could some day offer better results at a lower cost.

READ MORE: Millions on prescription sleeping pills would sleep through a fire alarm [EurekAlert]

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A new theory suggests that a mirror universe existed before the Big Bang

Since the 1950s, scientists have discovered that certain phenomena have the ability to violate some established symmetries of the universe. This is how it has now been proposed that our universe could be the reflected image of a universe of antimatter that extends backward in time before the Big Bang.

This has been suggested by a group of scientists from Canada. They have designed a cosmological model that raises the existence of an “anti-universe” that, like ours, has a fundamental rule of physics called “CPT symmetry”.

A fairly similar study was reported 3 years ago and suggested the existence of a mirror universe where time could be moved upside down.

What is the “science” here?

The phenomena that we mentioned in the first paragraph and that could violate some established symmetries of the universe are called parity (P), which is the idea that if you change all your spatial coordinates (up, down, inside, outside, right), physics will continue to behave in the same way. Another is called charge (C), which states that the change of matter to antimatter should lead to the same physics. But that is not always the case. At first, many of these violations were resolved using the combined CP symmetry, but then the researchers found violations in this as well, so they added time (T) to the equation. The principle says that something may be able to break one (or two) of the symmetries of physics, but nothing should be able to break the combined CPT symmetry.

Unlike the previous study, this new research uses this approach for the entire universe. They argue that the universe does not violate the CPT since our universe dominated by matter, expanding in a certain direction in the time since the Big Bang, is the mirror image of a universe dominated by antimatter that existed before the Big Bang.

This theory has some interesting advantages. It does not require us to build new physics to explain several complicated events in the evolution of the universe, such as ” Cosmic Inflation,” the extremely rapid expansion of the universe in the fraction of seconds after the Big Bang. It also presents a possible candidate for dark matter, since this configuration would produce an excess of hypothetical massive particles known as sterile neutrinos.

A new theory suggests that a mirror universe existed before the Big Bang

However, it is far from being a perfect theory. It does not explain, for example, the fluctuations of temperature in the cosmic microwave background: the universe must be full of radiation, which is the remnant of heat that remains of the Big Bang after the cooling of the gas, which has been a cornerstone of the cosmological models since its discovery.

Now, the team is working to solve these problems; and if they do, they may be able to respond if there is a mirror universe populated by “evil versions” of ourselves.

The scientific study has been published in  Physical Review Letters.

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