Newton’s Laws Sir Isaac Newton was the first to formulate ideas about how to describe the causes of motion. He came up with the universal laws in the book titled Philosophiae Naturalis Principia Mathematica (“Mathematical Principles of Natural Philosophy”)

Newton’s First Law In his own words, Newton states: “Every body preserves in its state of being at rest, or of moving uniformly straight forward, except insofar as it is compelled to change its state by force impressed.” Force- an interaction between two objects that may or may not affect the subsequent motion of either object.

Newton’s First Law cont. Force of Gravity- the force of gravity is the force that is responsible for accelerating objects at 9.8 meters/second squared near Earth’s surface. The force that gravity exerts still depends on the mass of the object. Equation= Force=(Mass)(Gravity)

Newton’s First Law cont. Force is defined by Newtons (N), such that (kilograms)(meters/second squared) Normal Force- the contact force that arises when two objects are impressed against each other. Its direction is always perpendicular to the surface of the object. Friction- comes about when two objects rub against each other.

Newton’s First Law cont. Static Friction- attempts to keep something stationary. Kinetic Friction- attempts to slow down moving objects.

Newton’s Second Law Newton’s second law is stated in the Principia as follows: “The alteration of motion is ever proportional to the motive force impressed: and is made in the direction of the right line I which that force is impressed.” This law is used to find a numerical answer to how force affects an object.

Newton’s Second Law cont. Usually written in equation form as: Fnet=ma Fnet stands for net force m stands for mass a stands for resulting acceleration of the object.

Newton’s Third Law In the Principia, Newton’s third law states: “To every action there is always opposed an equal reaction: or the mutual action of two bodies upon each other is always equal, and directed to contrary parts.” Action and Reaction forces will be equal in magnitude and opposite in direction, and these forces will act on different objects.

Newton’s Third Law cont. The key to understanding the third law is to realize that the action and reaction forces act on two different objects.