The laws of motion and universal gravitation

The laws of motion and universal gravitation

Newton's laws of motion.

Sir Isaac Newton (1642 - 1727), one of the most profound scientists of all time, interpreted and correlated many observatiorions in mechanics and combined the results into three fundamental laws, known as Newton's laws of motion.

First law of motion.

A body at rest remains at rest, and a boy in motion continues to move at constant speed along a straighr line, unless there is a resultant force actiong upon the body. The forst part of the law is evident from everyday experience; for instancem a book placed on a table remains at rest. The second part of the law is more difficult to visualize; it keeps on moving without the action of any further force. This statement is correct; the body would continue to move without any reduction of velocity if no force acted upon it.

Hower, expirience shows thet a retarding force is a always present in the nature of friction, If friction could be eliminated entirely, a body once set into motion on a level surface would continue to move indefinitely with undiminished velocity.

Therefore, uniform motion is a natural condition and maintains it self without the actionn of a resultant force, It is interesting to note that whether a body is at rest or moving with constant speed along a straight linem its acceleration is zero. Hence the first law of motion means that a body accelerates only while some resultent force acts upon it.

Second law of motion

The acceleration of body takes place in the direction of the resultant force acting upon it; the acceleration is directly proportional to the resultant force and inversley proportional to the mass of the body. Int general, the greater is the acceleration.

Third law of motion

For every action there is an equal and opposite reaction, and the two are directed along the same straight line. In this statement, the term "action" means the force that the second body exerts on the first. It should be noted that the action and reaction are never exerted on the same object. Thus, action and reaction, althouhg aqual and opposite, can never balance each other. Consequently, the first and second laws deal with forces on a single body; the third law deals with the mutual forces between two bodies.

Law of universal gravitation

Newton also showed that every particle in the universe attracts every other particle, and explained how this attraction is affected by masses of the particles and the distance separating them. The law reads: Each particle of matter attracts every other particle with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between them.

Pull of gravity - weight

The most familiar illustration of universal gravitation is the force of attraction which the earth exerts upon objects near it, causing the objects is restrained so that it cannot fall when released, the earth exerts the same force on it, but the pull of the earth is balanced by some equal and opposite force exerted by the restraining agent.

The force of attraction that the earth exerts on a body, that is, the pull of gravity on it, is called the weight of the body. The weight of a body is a force and can be treated in exactly the same way as any other force. Its direction is, however, always toward the center of the earth.

The concept of momentum

Among the concepts of physics that have to do with force and motion, one of the most fundamental is momentum. The momentum of a body is defined as the product of its mass and its velocity. This concept prompts a further consideration of Newton's second law of motion. This law states that a body acted upon by some resultant force undergoes a change of momentum which is equal to the impulse of that force (impulse is the product of a force and the time during which it acts). The impulse has the same direction as the velocities.

The law of conservation of momentum is a pricinple which states that the total momentum of an isolated system stays constand regardless of any interactions that may take place among its parts. The law is one the great generalizations of physics.