3. البندول المخروطي -1 (α)T
تؤثر قوتان على الجسم المتحرك: قوة الجاذبية وقوة التوتر.
حسب مستوى الحركة، بالنسبة لموقع مركز الدوران ، فإن قوة الجاذبة نحو المركز هي المركب الأفقي لقوة التوتر.
لنرسم مخططًا للقوى المؤثرة على الكرة:
نكتب معادلة الحركة الدائرية بالنسبة للمحور المتجّه نحو المركز، ومعادلة الحركة العمودية بالنسبة للمحور الرأسي الموجّه لأعلى:
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نقسم معادلتي الحركة على بعضهم البعض:
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نكتب بشكل مفصّل التعبير عن السرعة الزاوية ، ونعبر عن زمن الدورة:
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لذلك ، فإن تعبير زمن الدورة هو:
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