The Sun keeps all of the planets orbiting it because _____.
1.the law of universal gravitation states that an increase in mass causes an increase in gravitational force
2.the law of ellipses states that the planets orbit the Sun in circular patterns
3.the law of harmonies states that the motion of the planets will not stop unless an outside force is applied
4.the law of equal areas states that planets sweep equal areas in equal periods of time around the Sun