# Using a force gauge vs. scale

1. Jan 23, 2014

### momotime

I'm trying to make a fixture measure how much force it takes to deform various items.

However, digital force gauges costs upwards from while simple scales don't cost much at all. What's the difference between using a fancy force gauge and placing a digital scale underneath an item that's being compressed?

Thanks!

2. Jan 24, 2014

### CWatters

Nothing I can think of.

Edit: Except that not all cheap weighing scales are well calibrated. Some may also have hysteresis (eg you get a different result when the force is increasing vs decreasing). Presumably you aren't planning to send the experiment to another planet or up a mountain (eg no changes in g?)

3. Jan 24, 2014

### momotime

Thanks for the input! I think I figured it out though... I'm assuming scales can give a different reading from a force gauge because items can absorb energy, making the scale give a different reading than the force being acted upon the object?

Example -- if you use a scale to punch a wall, the maximum reading will reveal the force of your punch. But if you use a scale to punch a pillow, the absorption of force will cause the reading to change..........?

4. Jan 24, 2014

### Staff: Mentor

No - in both cases the scale is correctly recording the force that you're actually applying.

It takes much less force to compress a pillow than it does to compress a wall - and you cannot push on an object any harder than it pushes back on you.

5. Jan 24, 2014

### AlephZero

What Nugatory said, plus, if you are putting a force transducer underneath the object, as in your OP, you are not measuring "the force of your punch." You are measuring the force that is transmitted through the object and reacted against whatever it is resting on. The difference is the mass x acceleration of the object, if it changes shape when you punch it.