2. جسمان يتحركان على سطح أفقي غير أملس
2.2. شد الخيط بين جسمين مع الاحتكاك
نستخدم تعبير التوتر الذي وجدناه في القسم السابق:
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نعوّض تعبير التسارع الذي وجدناه:
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