# Hi.I am using a 3 axis accelerometer for motion detection. I can

1. Jun 10, 2010

### mark2468

Hi.

I am using a 3 axis accelerometer for motion detection. I can easily determine the tilt using simple triginometry but cannot determine the movement in a particular direction. For example the sensor is at 45 degrees to the floor so the x,z coordinates are x = 0.5, z = 0.5. So if I keep the angle constant and move directly up x will stay the same and z might now go to 1 or even more. But x = 0.5, z = 1 is also the same as the device being parallel to the floor. So is it possible to determine both 'dynamic' and 'static' acceleration using one of these devices or would I have to use more?

Thanks,

Mark.

2. Jun 12, 2010

### phyzguy

Re: acceleroneter

This is known as Einstein's "principle of equivalence". There is no way to distinguish acceleration from a gravitational field, no matter how many devices you use. So, for example, if all three readings are zero, you don't know if the device is here on Earth, falling at 9.81 m/s^2, or floating out in space somewhere. All you can measure is the local acceleration experienced by the device, which might be purely gravitational( what you called static), purely acceleration (what you called dynamic) or some mixture.