86.1 The gravitational force 2. Newtons law of universal gravitation ① The vector force F12=-G ,m , m2 I Gravitational force is always attractive force FE- FES FE ② The principle of linear superposition 86.1 The gravitational force ③ The value of g G is a fundamental constant of nature Quartz fiber Determined by experiment(Henry Cavendish): Mirror G≈667×101N.m2/kg2 2. Newton’s law of universal gravitation §6.1 The gravitational force 12 12 21 21 ˆ ˆ 2 1 2 21 2 1 2 12 r r m m F G r r m m F G = − = − r r 1 The vector force 2The principle of linear superposition Gravitational force is always attractive force. F12 r F21 F12 r r = − 12 rˆ 12 21 r =r 21 rˆ §6.1 The gravitational force 3 The value of G G is a fundamental constant of nature. Determined by experiment(Henry Cavendish): 11 2 2 ≈ 6.67×10 N⋅m /kg − G