Gravitational Force (Gravity)

• Newton and the apple.
• F = Gm_1m_2/r^2
• There is a force between any two objects (m_1 and m_2) that is proportional to their masses and inversely proportional to the square of the distance between them (r).
• G is the gravitational constant = 6.656e-11 N-m^2/kg^2
• The gravitational force acts along a line connecting the centres of the two objects.
• When an apple falls from a tree, it is pulled toward the centre of the earth.
• (The earth is pulled toward the apple too, but not very much as it's a lot bigger than the apple.)
• This fits in with the second law F = ma (a is acceleration).
• If you want to see the effect of one object on another (say the earth on an apple), let m_1 be (the apple) and m_2 earth.
• F = Gm_1m_2/r^2 = m_1a
• (reduce to) a = Gm_2/r^2