2. Weight of a body
• weight of the body is actually gravitational force acting on it.
• In statics and in dynamics we are interested to compute the weight of
the body.
3. Why we need Law of Gravitation
• The calculation mentioned in above slides requires law of gravitation.
• Which was also formulated by Newton's.
4. Law of Gravitation
• The law of Gravitation is
expressed by the follwoing
equation:
2
2
1
r
m
m
G
F
5. Continued......
• Where
• F = The mutual force of attraction between two particles.
• G = a universal constant known as the constant of gravitation.
• m1, m2 = the masses of the two particles.
• r = the distance between the centers of the particles.
6. About Mutual Forces and G
• The mutual forces F obey the law of action and reaction.
• Since these are equal and opposite.
• And directed along the line joining the centers of the particles.
• The of gravitation constant G is 6.673(10-11)m3/(kg.s2).
7. Gravitational Attraction of the Earth
• Gravitational forces exists between every pair of bodies.
• The gravitational attraction of eaarch on a body exists whetber the
body is at rest or in motion.
• This attraction is force as the weight of body should expressed in
Newtons in SI and Pounds in US customery units.
• W = mg
8. Principle of Transmissibility
• “A force may be applied at any
point on its given line of action
without altering the resultant
effects of the force external to
the rigid body on which it acts. “
