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Gravity and Motion

Chapter 5 Outline with Practice Quize Questions

 

* By Newton's time, work by Galileo, Kepler, Descartes, Hooke, and others had led to an understanding of inertial motion and the need for a central force to account for the curved paths of the planets around the Sun.


* Newton's law of inertia says that the momentum of an object remains constant unless it is acted on by an unbalanced force. The momentum of an object is the product of its mass and velocity.


* Newton's law of force says that when a force acts on a body, it causes a change in its momentum in the direction in which the force is applied. Usually, the law of force is expressed as F = ma.


* Newton's law of action and reaction says that when one body exerts a force on a second body, the second body exerts a force on the first equal in magnitude but opposite in direction.


* Newton's law of universal gravitation states that every two particles of matter attract each other with a force that depends on the product of their masses and varies inversely with the square of the distance between them. The law of gravitation is expressed as FG = GMm/d2.


* Angular momentum is the momentum associated with rotation or revolution. Angular momentum can be transferred from one object to another or redistributed. However, it is always conserved.


* Newton found that orbiting objects attracted to the Sun by the force of gravity obey Kepler's laws. He discovered a general form of Kepler's third law relating the separation, orbital period, and masses of any two orbiting bodies. This relationship is the basis of most astronomical mass determinations.


* Circular speed is the orbital speed of a body that moves in a circular orbit. The circular speed at a given orbital distance has the same value as the average orbital speed for an elliptical orbit having a semi-major axis equal to the circular distance.


* A body moving at escape velocity leaves the solar system on a parabolic path and never returns. At any distance from the Sun, escape velocity is the square root of 2 times the circular speed at that distance.


* Tidal forces are differences in gravitational force. They occur because the various parts of a body are in different directions and at different distances from the object attracting them. Tidal forces stretch the body in the direction toward and away from the attracting object. The strongest tidal forces are felt by large bodies near massive attractors.

Key Term

 
acceleration. acceleration of gravity angular. momentum. central force. centripetal acceleration.
centripetal force. circle. circular speed. conic section. ellipse. escape velocity .force gravitational. potential energy. hyperbola. inertia. inertial motion. kinetic energy. mass momentum. neap tide. parabola. spring tide. tidal force. tides velocity weight.

 

Practice quize with true answer

 

1. An object slows down in such a way that its acceleration is constant. What can we say about the force acting on the object? the force acting on it is constant


2. Suppose an object moves in a circular path at constant speed. What can be said about the force acting on it the force acting on it has constant strength


3. A mass of 50 grams is acted on by a force of 200 dynes. The motion of the object subsequently will beacceleration at a rate of 4 cm/sec/sec.


4. When a force is applied to a body with a mass of 10 kg, the acceleration of the body is 1 m/s/s. If the same force is applied to a body with a mass of 40 kg, what is the acceleration of the body? 0.25 m/s/s


5. The force required to keep an object in a circular orbit is directed toward the center of the circle


6. If the masses of the sun and Earth each were tripled, the force of gravity between them would go up by nine times


7. Suppose there is a planetary system in which a planet with an average distance of 6 AU from the star has an orbital period of 3 years. What is the mass of the star? 24 solar masses


8. A comet has a speed which is slightly smaller than escape velocity. What path around the sun will the comet follow? an ellipse


9. Why does the Earth have a tidal bulge on the side of the Earth which is opposite the moon. Lunar gravity is weakest there


10. As a consequence of tides the day is lengthening, the month lengthening 4. When a force is applied to a body with a mass of 10 kg, the acceleration of the body is 1 m/s/s. If the same force is applied to a body with a mass of 40 kg, what is the acceleration of the body ? 0.25 m/s/s


5. The force required to keep an object in a circular orbit is directed
toward the center of the circle


6. If the masses of the sun and Earth each were tripled, the force of gravity between them would go up by nine times


7. Suppose there is a planetary system in which a planet with an average distance of 6 AU from the star has an orbital period of 3 years. What is the mass of the star?
24 solar masses


8. A comet has a speed which is slightly smaller than escape velocity. What path around the sun will the comet follow? an ellipse


9. Why does the Earth have a tidal bulge on the side of the Earth which is opposite the moon?
lunar gravity is weakest there


10. As a consequence of tides. the day is lengthening, the month lengthening

 

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