Weight derivation from accelerometer readings?

lenovoguy

Hi there

I have a small software tool which displays the readings from a three axis accelerometer. I'm wondering if and how you could derive the weight of an object from these readings, using the accelerometer>

Morbert

lenovoguy wrote: »

Hi there

I have a small software tool which displays the readings from a three axis accelerometer. I'm wondering if and how you could derive the weight of an object from these readings, using the accelerometer>

Do you know the forces acting on the object?

MonkeyDoo

Apparently you can do it, if you attach the mass being measured along with the accelerometer to a spring.

You will need to calculate the spring constant(k). By hanging a known weight on the spring and measuring the change in length. Here is how to calculate this

http://answers.yahoo.com/question/index?qid=20090203022917AAZjU7s

Using the accelerometer you can then measure the period of oscillation of the spring mass system (T)

You can then calculate the mass using this equation

T = 2π sqrt(m / k), where T = period (seconds), m = mass (kg), k = spring constant (N/m)

The accelerometer is being reduced to being an accurate timer here,as you will probably get the accelerometer reading into your computer at a known I/O frequency, it's a round about way of determining mass.

I nicked this from here by the way ;-) I'm not a nerd ;-)

http://www.physicsforums.com/showthread.php?t=448446

himnextdoor

MonkeyDoo wrote: »

Apparently you can do it, if you attach the mass being measured along with the accelerometer to a spring.

You will need to calculate the spring constant(k). By hanging a known weight on the spring and measuring the change in length. Here is how to calculate this

You might as well just weigh it. LOL.

If you are thinking of weighing jets in flight for instance, then no, you can't derive weight.

A hovering helicopter and the same helicopter moving have the same mass but would register different values on your accelerometer.

SkepticOne

himnextdoor wrote: »

You might as well just weigh it. LOL.

Weighing in the normal sense of the word requires you to know the value of the gravitational field at the point where the object is weighted. What if you don't have that e.g. on a platform in non-uniform motion or in orbit?

What MonkeyDoo describes is the method used by astronauts to "weigh" things in space. They can't use gravity so they attach it to a spring of known stiffness and time the oscillations. If you were on a platform that was in non-uniform motion you couldn't use gravity either so something along these lines would also have to be used. In neither case, of course, would you be "weighing" the object in the strict sense of the word.

Professor_Fink

lenovoguy wrote: »

I have a small software tool which displays the readings from a three axis accelerometer. I'm wondering if and how you could derive the weight of an object from these readings, using the accelerometer>

If you mean by the change in the gravitational force it feels, then I am afraid you are out of luck. The gravitational force is given by G M_Earth M_Object/R_Earth^2. However, since acceleration = force/mass, the acceleration due to gravity is constant for all masses (approximately 9.81 meters per second^2), so the accelerometer will always give the same reading.