# 42 kg in a weighing machine

1. Dec 27, 2008

### DrChem

if our weight is 42 kg in a weighing machine , in reality is it more or less than 42 kg?

2. Dec 27, 2008

### csprof2000

Re: weight

If a machine measures your weight to be 100 lbs, and the machine is not accelerating (at any rate, not accelerating quickly), and there are no extenuating circumstances, and the machine is well-oiled and frictional forces are neglible, and if the weighing machine measures correctly (that is, it doesn't measure the same weight differently depending on how much weight is already on it)... then I would say it's probably exactly right.

If the machine is more realistic, I guess it depends on how the machine's made.

I imagine most real machines get your weight a little low, due to frictional forces. Plus, they probably sell more scales that way.

3. Dec 27, 2008

### pallidin

Re: weight

Adding to the previous post, I know that some food service scales and postal scales have a zero weight calibration feature, which helps accuracy of a weighted measurement.

4. Dec 27, 2008

### Gnosis

Re: weight

"Mass" (represented in kg’s) refers to a “quantity of matter”. Therefore, our “weight” is merely a consequence of the gravitational field in which our mass is placed and then “weighed”.

On the moon, we‘d weigh roughly 6 times less than on the surface of the Earth, but our “mass” would be identical in either location, just as our “mass” would remain identical if we were placed anywhere else in the universe.

Weight is therefore defined by:

w = mg

where,

weight (in Newtons) = mass (in kg) x gravity (in m/s^2, which is 9.8 m/s^2 on Earth)

For instance, if your “mass” were 42 kg, on Earth you’d weigh:

42 kg x 9.8 m/s^2 = 411.6 Newtons (or 92.52768 pounds)

Pounds = .2248 x Newtons