Ch4_malleys

=Newton's Laws= toc

Newton's First Law of Motion
What is Newton's First Law? - “An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force” - No change in motion unless an unbalanced force acts on the object; otherwise it will move at constant speed in a straight line - Objects will “keep on doing what they’re doing”
 * Predicts the behavior of stationary objects
 * Predicts the behavior of moving objects
 * Really Galileo's idea

Inertia and Mass
What are the roles of mass and inertia in Newton’s Laws? - **Inertia** – the resistance an object has to change in its state of motion; in other words, the tendency to resist change in their state of motion - Inertia is a property of matter; it can be determined using mass (measures how difficult it is to change an object's motion) - Mass (Kg) ≠ weight (weight is the pull of gravity on the mass) - Before Newton, people believed it was the natural tendency of all objects to assume a rest position; they only needed a force to act What did Galileo have to do with inertia? - Galileo developed the concept of inertia - He reasoned that moving objects eventually stop because of friction - He did experiments that involved balls and inclined planes facing each other in order to make these discoveries What do forces do (as far as Newton's First Law is concerned)? - Newton’s first law declares that a force is not needed to keep an object in motion - Objects do not come to rest position because of the absence of the force; it is the presence of a force - Forces bring things to rest What is mass (particularly in relation to inertia)? - Some objects have more inertia than others - The tendency of an object to resist changes in its state of motion varies with mass - Mass is solely dependent upon the inertia of an object (a more massive object has a greater tendency to resist changes in its state of motion)

States of Motion
What roles do acceleration and velocity play? - Inertia is the tendency of an object to resist changes - The state of motion is defined by its velocity - An object at rest has zero velocity and (without an unbalanced force) will remain with zero velocity; it will not change its state of motion - Inertia can also, therefore, be described as the tendency of an object to resist accelerations

Balanced and Unbalanced Forces
What are balanced and unbalanced forces? - Equilibrium – when there is no unbalanced force; the object maintains its state of motion - Unbalanced forces cause acceleration - It will accelerate in the direction of the unbalanced force - To determine if the forces acting upon an object are balanced or unbalanced, an analysis must first be conducted to determine what forces are acting upon the object and in which direction =**Force and Its Representation**=
 * Static equilibrium - no motion (at rest)
 * Dynamic equilibrium - constant speed
 * In either case, the forces are balanced
 * If two individual forces are of equal magnitude and opposite direction, then the forces are said to be balanced
 * An object is said to be acted upon by an unbalanced force only when there is an individual force that is not being balanced by a force of equal magnitude and in the opposite direction

The Meaning of Force
What is the meaning of force? - A force is a push or pull upon an object resulting from the object’s interaction with another object - Either contact forces or action-at-a-distance forces - Vector quantity, measured in Newtons (N); I N = 1 kg m/s/s
 * Forces only exist as a result of an interaction
 * Contact forces – results when two interacting objects are perceived to be physically in contact with each other
 * Action-at-a-distance forces – result even when the two interacting objects are not in physical contact with each other, yet are able to exert a push or pull despite their physical separation

Types of Force
What are the types of forces? - Contact forces – frictional, tension, normal, air resistance, applied, spring - Action-at-a-Distance forces – gravitational, electrical, magnetic What is the difference between mass and weight? - Weight – the force of gravity acting upon an object - Mass – the amount of matter that is contained by the object - The mass will be the same no matter where it is located What is the difference between static friction and sliding friction? - Sliding friction – results when an object slides across a surface - Static friction – results when the surfaces of two objects are at rest relative to one another and a force exists on one of the objects to set it into motion relative to the other object
 * Applied force – applied to an object by another object
 * Gravity force – the force with which the earth, moon, or mother massive object attracts another object towards itself; Fgrav = mg
 * Normal force – the support force exerted upon an object that is in contact with another stable object
 * Friction force – force exerted by a surface as an object moves across it/makes an effort to move across it
 * Air Resistance Force – a special type of frictional force that acts upon objects as they travel through the air
 * Tension force – the force that is transmitted through a string, rope, cable, or wire when it is pulsed tight by forces acting from opposite ends
 * Spring force – the force exerted by a compressed or stretched spring upon any object that is attached to it

Drawing Free-Body Diagrams
Why draw free-body diagrams? - They are used to show the relative magnitude and direction of all forces acting upon an object in a given situation? - Can depict four forces acting on the object

Determining the Net Force
How do you determine the net force? - A net force = unbalanced force - Net force is the vector sum of all the forces that act upon the object =Newton's Second Law of Motion=
 * This takes into account the fact that a force is a vector and two forces of rqual magnitude and opposite direction will cancel each other out (balanced forces

Newton's Second Law
What is Newton's second law? - Newton’s second law of motion pertains to the behavior of objects for which all existing forces are not balanced - The acceleration of an object is dependent upon two variables – the net force acting upon the object and the mass of the object - Formally stated: The acceleration of an object as produced by a net force is directly proportional to the mass of the object - a = Fnet/m or Fnet = ma

The Big Misconception
What is the big misconception? - The idea that sustaining motion requires a continued force - Overcoming misconceptions requires becoming aware of them and considering an alternative explanation, and then adopting a new, more reasonable one - Remember that an unbalanced force causes acceleration; the acceleration is in the same direction as net force