# (16) Newton's Laws of Motion1.   Force and Inertia

Index

13. Free Fall

14. Vectors

15. Energy

16. Newton's Laws

17. Mass

17a. Measuring Mass
in Orbit

17b. Inertial balance

18. Newton's 2nd Law

18a. The Third Law
 Isaac Newton

Isaac Newton was born in 1642, the year Galileo died. Almost all his creative years were spent at the University of Cambridge, England, first as a student, later as a greatly honored professor. He never married, and his personality continues to intrigue scholars to this day: secretive, at times cryptic, embroiled in personal quarrels with some scholars yet generous to others, bestowing his attention not just on physics and mathematics, but also on religion and alchemy.

The one thing about which everyone agrees is his brilliant talent. Three problems intrigued scientists in Newton's time: the laws of motion, the laws of planetary orbits, and the mathematics of continuously varying quantities--a field nowadays known as [differential and integral] calculus. It may be fairly stated that Newton was the first to solve all three. No wonder that the poet Alexander Pope, who lived in Newton's time, wrote:

Nature and Nature's laws lay hid in night
God said:"Let Newton be!" and all was light.

 "Newton's three Laws of Motion" are the foundation of the theory of motion--e.g., of orbits and rockets.     This section discusses two concepts on which they are based: Force     and     Inertia

For later reference, Newton's three laws are listed below the way they are usually formulated :

 In the absence of forces, ("body") at rest will stay at rest, and a body moving at a constant velocity in a straight line continues doing so indefinitely. When a force is applied to an object, it accelerates. The acceleration a is in the direction of the force and proportional to its strength, and is also inversely proportional to the mass being moved. In suitable units: a = F/m or in the form usually found in textbooks F = m a More accurately, one should write F = ma with both F and a vectors in the same direction (denoted here in bold face). However, when only a single direction is understood, the simpler form can also be used. "The law of reaction," sometimes stated as "to every action there exists an equal and opposite reaction." In more explicit terms: Forces are always produced in pairs, with opposite directions and equal magnitudes. If body #1 acts with a force F on body #2, then body #2 acts on body #1 with a force of equal strength and opposite direction.

Author and Curator:   Dr. David P. Stern
Mail to Dr.Stern:   stargaze("at" symbol)phy6.org .

Last updated: 10-9-2004
Reformatted 24 March 2006