## Introduction: Make a Simple Hygrometer for 0\$ !! (great for Your Childrens!)

Since I posted my last instructable about simple science (you can check it out here) it get 41,501 views, so I decided to post another one. And today you will learn how to make a simple hygrometer, Another project that is fun to make with kids, and it is educational as well.

If you're curious about how it works, check last step ;)

## Step 1: You Will Need...

Here are the things you will need to make the hygrometer:

1. Scissors
2. Sharpie, or a pen
3. piece of paper (preferably thicker than regular printing paper, i used 180g/m^3)
4. piece of cardboard/thin plywood/something that you can pin the pin into
5. ONE hair, preferablu longer than mine - about 5-7 cm long

I Highly recommend to use horse hair. It reacts better and more noticeably than human hair.

But unfortunately my horse was drinking beer in the pub.... so I used my hair. ;)

## Step 2: OK! Now We Can Start Learning.

Try to draw an arrow on paper, it don't have to be big, look at mine arrow, it can be similar. Then you have to cut it out using scissors.

Remember! always be careful using scissors and don't let kids to play with them when you are not around.

Now the most important part, You have to make hole in arrow and make a pivot point. The hole need to be a little bigger than pin so the arrow can move freely. You can check it by twisting the pin - when arrow always point down no matter which way you turn the pin.

When you finish arrow pin it to the cardboard/plywood and check if the arrow spins freely.

## Step 3: Tape the Hair to the Arrow and Cardboard.

Cut small piece of tape and stick it to the hair and then to the arrow. Pin the arrow to the cardboard and tape the other end of hair to it.

Basically you finished ;) But I have added some graphics to it, so it look quite better.

## Step 4: But... How It Works?

Here is how it works:

Hair have special hidden ability to shrink when dry and expand when wet. Using this fact, when there are more moist in air the hair will be longer and the arrow will point more downwards. When the air is dry, the hair will shrink and move arrow upwards.

The longer the hair is the more visible is arrow movement. You can use horse hair to make it more visible, since horse hair reacts stronger on humidity changes and moves arrow more visibly.

It's a project great to make with children and show them some science ;) but you can use it to check the changes in air humidity in your room ;)

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