How would an iPad’s gravity sensors work aboard the ISS, which is in a state of constant freefall, and thus experiences zero-g all the time? Would the screen tilt feature work aboard the ISS? Would “down” point to the Earth, since that is where an overwhelming number of gravitons come from?
And how would the situation differ (if at all) in deep space, far from gravitational sources? Would the iPad begin responding to the galactic gravitational tide?
I think no commercially available device would have that sensitive a gravity-sensing mechanism, so the question is more theoretical than practical. But the question is nevertheless interesting, at least to me.
The accelerometer on the iPad will sense freefall, exactly as if it had just been dropped but hadn’t hit the floor yet. Some laptops have a feature that will cause them to park the drive if they sense freefall, to protect against a head crash when they hit the floor, but I don’t know if the iPad has any special action it takes when falling. It won’t be able to sense which direction the Earth is, so it won’t reorient its screen according to how it’s being held, but if an astronaut is carrying it while moving around the inside of the ISS the iPad will sense momentary accelerations as a result of that and may rotate its screen as a result.
The “gravity sensor” is a 3-axis accelerometer, i.e. it measures the X, Y and Z components of acceleration to find out the magnitude and direction of acceleration. Under normal use on the ground, the X,Y,Z measurements will add up (vector sum) to 1G. In free fall, all 3 measurements would be zero, or very close to it. If the astronaut is holding it and moving it around, the sensor will measure the acceleration, but it wills till be very small compared to gravitational acceleration on the ground.
I don’t know specifically how the iPad would interpret these <<1G numbers. I imagine the screen auto-rotation won’t happen unless there is a reliable measurement of gravity, i.e. the numbers add up to close to 1G.
How does it differentiate acceleration due to gravity from other forms of acceleration? I mean, the IPad behaves the same inside a rapidly accelerating train or car.
Nah, you just need a more expensive sports car. The Veyron, for example, with about a $2MM sticker price, has better acceleration than Earth’s gravity.
I happily volunteer to test an iPad in a Veyron. For science.
There’s no gravity in the frame of reference of an orbiting spacecraft – I think there was another thread here that reflected a similar misconception. So anything that depended on gravity would behave just exactly as it would in interstellar deep space. If there was an iPad on the ISS, the accelerometer would no longer be able to sense the horizontal/vertical orientation, and also my game of “Plunk!” would no longer work! What I’d be curious about is just how confused the GPS would be. My guess is that it would never be able to hold a lock on enough satellites long enough to give you any info at all.
My guess is that it would never be able to hold a lock on enough satellites long enough to give you any info at all.