On September 2, 2017, instagram @warungsaintek uploaded the following picture:

Well, in this article will be informed how to calculate the depth of the well/the abys**s just by building a stone and a stopwatch**. The more accurate stopwatch (able to measure the more numbers behind the comma, as 2.32 seconds) then it will be the more accurate calculation of its depth. Neither the accuracy/precision will also increase if we are hearing great response, and then whether to do with calculating the depth of the well/the abyss? Prepare your stationery and paper! Ready-ready to accept the fact that it turns out it’s engrossing and rewarding Physics:)

**The first step **is to choose the stone. Stones used should not be too large, stone the size of a grape is enough. The size of the stone becomes important because it deals with air resistance experienced by a stone. The greater the size or width of the stone, then air resistance becomes increasingly large and must be incorporated into the calculation of the depth of the well/the abyss. Conversely, if the size of a small stone so air resistance is not too influential and can be ignored. But do not be too small, we’ll have problems listening to sound when a rock on the surface of the bottom of the well or the abyss (his voice too softly).

**The next step **is to formulate simple language or parameter is declared anything observable into simple shapes and unique. Like Apple stated in letter a, the gua*v*a is expressed in the letter j (g*ua*va cannot be expressed in the form of ja, becau*se* it would be confused with the Apple).

1. There are two stages of time events

- First: the time required by the stone to get to the surface of the water of the well or the abyss stated i
*n*_{t1.} - Second: the time required by the sound due to the collision with the surface of the stone water wells or the chasm to get to our ears is called
*t*. So know right why auditory response we must be nice? Just a little late because if we press the button to stop the stopwatch, th_{2}*e*t2 is not accurate. As a result? Calculation of depth become inaccurate. Therefore, if you want to get a high accuracy in the calculation of the depth of the well/the abyss, it is important to repeat the process several times until the stoning, the average value of time._{n}

Total time from both of these stages revealed with* T*, where* T = _{t}1 + t_{2}*

2. The depth of the pit or chasm revealed by *h*

3. The speed of the sound wave is expressed with a* v*

4. The force of gravity is expressed with* g*

**The third step and the last step is al**so doing the calculation, the calculation is simple.

The motion of free fall (X-grade Physics subjects in HIGH SCHOOL), we know that

And of the formulation of the speed of the wave (the subjects of physics class VIII JUNIOR HIGH SCHOOL), we know that

Enter the value* o _{f}* t1 a

*nd*t2 to calculate the total time T T keruas and m

*o*ve right, then it is obtained:

From the equation above, shall we search is depth (*h*). So hi*s* days are numbered h, then the denominat*o*r v on tribe

both should be removed. Therefore, both sides are multiplied by v *s*o that it becomes

Remember the quadratic equation? Yes, the above equation is actually a form of the quadratic equation. For example, then the equation above becomes

Or it can be compiled into a raw form of the quadratic equation becomes:

Using the formula f* or abc (su*bjects of mathematics class IX JUNIOR) to find the roots of the above equation, then acquired the form of H, i.e.:

Grab a positive price to get the value of H, not* may*be right depth is negative? But remember, change back the value of H with √ *h,* so that the obtained** formulae well** depth/the abyss as follows:

**Example case:**

Suppose we threw stones and hear the voice of rock that touches the surface of the bottom of the well/the abyss within 2 seconds (calculated at the time of the throw stones to terdengarnya votes). Then how well depth/jurangnya?

Formula calculate depth, there are three parameters that we need time, i**.e., the speed of sound, and gravity**. The speed of sound is usually valued at 340 m/s, and gravity is worth 10 m/^{s}2, then

*T* = 2 s

*v* = 340 m/s

*g* = 10 m/s^{2}

Inserted in the formula, then retrieved through the well depth calculation calculator is **18.9 m**. Oh yes, so in addition to stone and a stopwatch, we also need a calculator and stationery to count, hehe. Unless our nice math skills like Figure Latitude in Laskar Pelangi, we can count them in the ground using a twig tree.

**The issue in this paper inspired by the Essay Q**uestion No. 4 OSN Physics level District/Municipality of the year 2005

Other interesting physics problem can be read in the book “HIGH SCHOOL Physics Olympiad” made by Intersolusi and published by SSC Eason in the year 2012.

Dosen dan peneliti, menekuni bidang Fotonika dan sensor. Sangat mencintai aktivitas membaca dan mendesain. Profil lebih lengkap dapat dilihat di ugm.id/siddiq .