3. Intro to Physics II: Newton's Laws AP: Module #9: BJ4 Physical Science: Chap 12 - 14 Text: Module 10 pp 229 - 254 Reading Assignments Module 10 pp 229 - 240 Module 10 pp 240 - 254 Homework Assignment Module 10 Study Guide (p. 253 # 1- 11) Module 10 Study Guide (p. 254 # 12- 17)

Introduction and Sir Isaac Newton (p 229) Newton's First Law (P 230): "Every body perseveres 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." This law is also called the law of inertia. This is often paraphrased as "zero net force implies zero acceleration", but this is an over-simplification. As formulated by Newton, the first law is more than a special case of the second law. Newton arranged his laws in hierarchical order for good reason (e.g. see Gailili & Tseitlin 2003).[2] Essentially, the first law establishes frames of reference for which the other laws are applicable, such frames being called inertial frames.

Friction Friction (p 237): Friction is the force of two surfaces in contact. It is not a fundamental force, as it is derived from electromagnetic forces between atoms. When contacting surfaces move relative to each other, the friction between the two objects converts kinetic energy into thermal energy, or heat. Friction between solid objects is often referred to as Dry Friction and frictional forces between two fluids (gases or liquids) as Fluid Friction. In addition to these there is also Internal Friction which illustrates a body's ability to recover from external deformation.

Newton's Second Law (p 240): The law of acceleration: "The rate of change of momentum of a body is proportional to the resultant force acting on the body and is in the same direction." Newton's second law of motion pertains to the behavior of objects for which all existing forces are not balanced. The second law states that the acceleration of an object is dependent upon two variables - the net force acting upon the object and the mass of the object. The acceleration of an object depends directly upon the net force acting upon the object, and inversely upon the mass of the object. As the force acting upon an object is increased, the acceleration of the object is increased. As the mass of an object is increased, the acceleration of the object is decreased.

Static and Kinetic Friction (244): Static friction: Static friction occurs when the two objects are not moving relative to each other (like a rock on a table). The coefficient of static friction is typically denoted as μs. The initial force to get an object moving is often dominated by static friction. The static friction is in most cases higher than the kinetic friction. Rolling friction occurs when one object "rolls" on another (like a car's wheels on the ground). This is classified under static friction because the patch of the tire in contact with the ground, at any point while the tire spins, is stationary relative to the ground. The coefficient of rolling friction is typically denoted as μr. Limiting friction is the maximum value of static friction, equal to the force applied to a body on the verge of motion across a surface.

Kinetic friction: Kinetic (or dynamic) friction occurs when two objects are moving relative to each other and rub together (like a sled on the ground). The coefficient of kinetic friction is typically denoted as μk, and is usually less than the coefficient of static friction. From the mathematical point of view, however, the difference between static and kinetic friction is of minor importance: Let us have a coefficient of friction which depends on the sliding velocity and is such that its value at 0 (the static friction μs ) is the limit of the kinetic friction μk for the velocity tending to zero. Then a solution of the contact problem with such Coulomb friction solves also the problem with the original μk and any static friction greater than that limit. Since friction is exerted in a direction that opposes movement, kinetic friction usually does negative work, typically slowing something down. There are exceptions, however, if the surface itself is under acceleration. One can see this by placing a heavy box on a rug, then pulling on the rug quickly. In this case, the box slides backwards relative to the rug, but moves forward relative to the floor. Thus, the kinetic friction between the box and rug accelerates the box in the same direction that the box moves, doing positive work. Examples of kinetic friction:

Sliding and Rolling Friction * Sliding friction is when two objects are rubbing against each other. Putting a book flat on a desk and moving it around is an example of sliding friction * Fluid friction is the friction between a solid object as it moves through a liquid or a gas. The drag of air on an airplane or of water on a swimmer are two examples of fluid friction. Rolling friction: Rolling friction is the frictional force associated with the rotational movement of a disc or other circular objects along a surface. Generally the frictional force of rolling friction is less than that associated with kinetic friction. Typical values for the coefficient of rolling friction are .001. One of the most common examples of rolling friction is the movement of motor vehicle tires on a roadway, a process that generates heat and sound as by-products.

Newton's Third Law (p 247): The law of reciprocal actions This law of motion is commonly paraphrased as: "To every action force there is an equal, but opposite, reaction force". A more direct translation is: To every action there is always opposed an equal reaction: or the mutual actions of two bodies upon each other are always equal, and directed to contrary parts. All forces occur in pairs, and these two forces are equal in magnitude and opposite in direction.