# The Gravitational Field

 Q:     "Why is it that if the mass of the earth increased, your weight would correspondingly increase, but if the mass of the sun increased, your weight would not be affected at all?  How does gravitational force works on this situation?" A:    It is not true that the weight of a person on the surface of planet Earth is not affected by the mass of the sun or of any other celestial object.  We usually disregard the attraction of object at the earth's surface by other celestial bodies in the universe.  Within the limits of this approximation, the weight of an object at the earth's surface is determined only by the force of attraction applied on it by the mass of the earth.  If the mass of the earth is increased (without changing the radius of the earth - this radius representing the distance between the center of mass of the object and the center of mass of the earth) then the gravitational force of attraction of the body by the earth is increased proportionally:  F = G (mobject * m earth) / r2 Q:     What must the separation be between a 5.0 kg particle and a 2.5 kg particle be in order for their gravitational attraction to be 3.0 X 10-12 N? A:    The force between the two particles is given by the equation where m1 and m2 are the masses, r is the distance of their separation, and G is the universal gravitational constant 6.67 m3 / (s2 kg). Now we need to solve for r r 2 = (G m 1 m2 ) / F  =>  Now we plug in the values and solve for r:                                                                                                     r = 16.7 meters

## References

### Kepler's Laws

The Law of Orbits
All planets move in elliptical orbits, with the sun at one focus.

The Law of Areas

A line that connects a planet to the sun sweeps out equal areas in equal times.

The Law of Periods
The square of the period of any planet is proportional to the cube of the semimajor axis of its orbit.

### Equations

Newton's Law of Gravitation

Superposition principle
Gravitational Acceleration
Gravitation within a Spherical Shell
Gravitational Potential Energy
Potential Energy of a System
Escape Speed
Law of Periods
Energy in Planetary Motion

# Mechanics List of Topics

 Measurements Newton's Laws Potential Energy and Conservation of Energy Rotation of Rigid Bodies Elasticity Vectors Forces and Fields Linear Momentum Angular Momentum Mechanical Oscillations Motion of Point-Mass Objects in One Dimension The Gravitational Field Collisions Torque Mechanical Waves Motion of Point-Mass Objects in Two and Three Dimensions Kinetic Energy and Work Circular Motion of Point-Mass Objects Equilibrium Sound

ครั้งที่

เรื่องการทดลองเสมือนจริง