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Measuring the Height of a Pyramid by Its Shadow — Thales' Similar Triangles
Around 600 BC the Greek philosopher Thales of Miletus astonished the Egyptians by finding the height of the Great Pyramid without climbing it — using only its shadow and a stick. His insight was that under the same sun, every upright object and its shadow form the same shape of triangle, just at different sizes. So the ratio of a stick's height to its shadow is exactly the ratio of the pyramid's height to its shadow. This blueprint reproduces Thales' method with a vertical staff and a measuring cord — the birth of measuring the unreachable by proportion.
نیا سیکھنے والا
2
ہدایات
1
1
Understand the principle
Understand the principle
The Sun's rays strike everything at the same angle at a given moment, so a tall object and its shadow make a triangle the same shape as a short stick and its shadow — only larger. Because the triangles are similar, height ÷ shadow is the same for both. Measure the stick and its shadow, measure the object's shadow, and proportion gives the object's height.
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Set up a vertical staff
Set up a vertical staff
Stand a straight staff upright on level ground and check it against a plumb line so it is truly vertical. Measure and record its height above the ground exactly.
اس مرحلے کے لیے مواد:
Dowel Rod1 pieceدرکار اوزار:
Cotton Kitchen String3
3
Measure the staff's shadow
Measure the staff's shadow
Measure the length of the staff's shadow from its base to the tip, and mark the tip with chalk so you can measure the tall object's shadow at the very same moment. Both shadows must be read together.
درکار اوزار:
Cotton Kitchen String
Chalk Line4
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Use the simplest moment (Thales' trick)
Use the simplest moment (Thales' trick)
The classic shortcut: wait until the staff's shadow is exactly as long as the staff is tall — the Sun is then at 45°. At that instant every vertical object's shadow equals its own height, so you can read the pyramid's height straight off its shadow.
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Measure the tall object's shadow
Measure the tall object's shadow
Measure the shadow of the pyramid, tower or tree from the point directly below its top to the shadow tip. For a pyramid, add half the base width, because the shadow starts from the centre of the base, not the edge.
درکار اوزار:
Cotton Kitchen String6
6
Apply the proportion
Apply the proportion
Compute the height with similar triangles: object height = object shadow × (staff height ÷ staff shadow). If you used the 45° trick, staff height ÷ staff shadow = 1, so the object's height simply equals its shadow.
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Work a numerical example
Work a numerical example
Say a 1 m staff casts a 2 m shadow — the ratio is 0.5. A tower whose shadow measures 30 m is therefore 30 × 0.5 = 15 m tall. The Great Pyramid, with a shadow scaled the same way, gives its own height of about 146 m.
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Check on level ground
Check on level ground
The result is exact as long as both shadows are measured at the same instant and the ground is level. Test it on a building of known height to confirm your measuring before trusting it on something you cannot reach.
منسلک بلیو پرنٹ مواد
متعلقہ بلیو پرنٹ
یہ بلیو پرنٹ علم بانٹتے ہیں — تکنیک، مواد یا اصول
CC0 پبلک ڈومین
یہ بلیو پرنٹ CC0 کے تحت جاری کیا گیا ہے۔ آپ اجازت لیے بغیر اس کام کو نقل، ترمیم، تقسیم اور کسی بھی مقصد کے لیے استعمال کرنے کے لیے آزاد ہیں۔
میکر کی حمایت کریں ان کے بلیو پرنٹ کے ذریعے پروڈکٹس خرید کر جہاں وہ میکر کمیشن وینڈرز کی طرف سے مقرر، کماتے ہیں، یا اس بلیو پرنٹ کی نئی تکرار بنائیں اور آمدنی شیئر کرنے کے لیے اسے اپنے بلیو پرنٹ میں کنکشن کے طور پر شامل کریں۔