How does a force gauge work?
When it comes to explaining a force gauge, you can explain it well using a spring balance, as this is actually a force gauge. This is easy to explain and well supported by a demonstration.
Preliminary test for the dynamometer
A force gauge enables you to assign a numerical value in N to a force. First of all, the weight force is well suited to explain how this works:
- Use the spring to show that a weight elongates it when you hang a weight on it, for example an empty water canister.
- Now put some water in the canister so that you can see that the spring gets longer the more weight you hang on it.
This shows that the more force is exerted on a spring, the more it expands. A force gauge works according to the principle.
This is how the force measurement works
There are very different feathers. You now need one that is suitable for a weight of 5 to at least 20 N.
If you have several springs, you can put them in a similar way to resistors in one ...
- Insert the spring into the thinner tube. There must be a hook at the bottom of the spring that looks out of this tube. Attach the tube to the spring so that it is fixed at the bottom where this hook is. The rest of the spring must not be attached to it. The tube must not be too long, because a piece of the spring must protrude at the top and there must be a loop on which you can grip the spring.
- Now slide the other tube over the first tube and attach it to the other end of the spring. When you pull the hook, the spring and inner tube come out.
- The dynamometer works on the principle that the harder you pull the spring with the inner tube, the more it comes out, i.e. the more force you use. You have now established a connection between the inner tube, the outer tube and the pulling force. This is also how a purchased force gauge works.
Now all you need is a scale.
Scale so that the dynamometer works
You have now sufficiently explained the relationship between the force and the length of the spring. Now it's about concrete measurements. The force gauge needs a scale on which you can read off the magnitude of the force.
- Hang the empty canister on the hook on the spring. The inner tube comes out a little. Since you do not know what force the empty canister exerts, this is of no use to you at first. Mark the point where the inner tube joins the outer tube with a line on the inner tube and write 0 on it (empty canister).
- Since 1 kg of mass exerts a weight of 9.81 N on the earth, the mass that exerts a force of 1 N is equal to 102 g. You also know that water has a density of 1. 102 g is therefore 102 ml. Now pour 510 ml of water into the canister. The inner tube comes out a little. Mark the inner tube again as described and write 5 N on it.
- Pour another 510 ml into the canister and mark 10 N and so on. Until the whole gamut is filled. Loosen the outer cardboard tube and reattach it, but so that the zero value can be seen exactly at the beginning of the tube.
- If you pull on the spring now, you can use it to measure the force you are applying. So this is how a dynamometer works. You can use it not only to weigh something, but also, for example, to measure the force with which a dog pulls on a leash or with which a car can pull and so on. Just read off a few values.
As you explain how a dynamometer works, point out that there are different springs. So there is no connection in the sense that 5 N always mean 10 cm in length, how much springs expand depends on the respective spring constant.
