Ch4_SteeleM


 * __Lesson 1__: Newton's First Law of Motion **


 * a) Newton's First Law**

S = Survey Q = Question R = Read R = Recite R = Review with dog!
 * 1) What is Newton's First Law?
 * 2) What are everyday applications of Newton's First Law?
 * 1) __Newton's First Law (law of inertia)__: 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.
 * 2) __Everyday applications__: The behavior of coffee in a coffee cup filled to the rim while starting a car from rest or while bringing a car to rest from a state of motion (coffee "keeps on doing what it is doing"). A person's body in a car while it is braking to a stop.


 * b) Inertia and Mass**

S = Survey Q = Question R = Read R = Recite R = Review with mom.
 * 1) What was Galileo's concept of inertia?
 * 2) Why don't forces keep objects moving?
 * 3) How is mass a measure of the amount of inertia?
 * 1) __Galileo's concept of inertia__: Moving objects eventually stop because of a force called friction.
 * 2) __Why forces don't keep objects moving__: An object in motion on a flat surface does not come to a rest position because of the absence of a force; rather it is the presence of a force (friction) that brings the object to a rest position. In the absence of friction, the object would continue in motion with the same speed and direction forever.
 * 3) __How mass is a measure of the amount of inertia__: The tendency of an object to resist changes in its state of motion varies with mass. The more inertia an object has, the more mass it has. A more massive object has a greater tendency to resist changes in its state of motion.


 * c) State of Motion**

S = Survey Q = Question R = Read R = Recite R = Review with mom.
 * 1) What does the phrase "state of motion" mean?
 * 1) __An object's state of motion__: The state of motion of an object is defined by its velocity. Inertia = the tendency of an object to resist changes in its velocity. Inertia = the tendency of an object to resist accelerations.


 * d) Balanced and Unbalanced Forces**

S = Survey Q = Question R = Read R = Recite R = Review with mom.
 * 1) What are balanced and unbalanced forces?
 * 2) What does it mean if an object is at equilibrium?
 * 1) __Balanced and unbalanced forces__: Balanced forces = forces acting upon an object that are of equal magnitude and in opposite directions. Unbalanced forces = forces acting upon an object that are NOT of equal magnitude and are NOT in opposite directions.
 * [[image:http://www.physicsclassroom.com/Class/newtlaws/u2l1d3.gif width="309" height="178" align="bottom"]]
 * 1) __Equilibrium__: When there is no unbalanced force acting upon an object; object maintains its state of motion, no acceleration.

__Lesson 2__: Force and its Representation

 * a) The Meaning of Force**

S = Survey Q = Question R = Read R = Recite R = Review with dog!
 * 1) What is the meaning of force?
 * 2) What are contact forces?
 * 3) What are at-a-distance-forces?
 * 4) What is a Newton?
 * 1) __Meaning of force__: A **force** is a push or pull upon an object resulting from the object's //interaction// with another object. When the //interaction// ceases, the two objects no longer experience the force.
 * 2) __Contact forces__: **Contact forces** result when the two interacting objects are perceived to be physically contacting each other. Examples: frictional forces, tensional forces, normal forces, air resistance forces, and applied forces.
 * 3) __At-a-distance-forces__: **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. Examples: gravitational forces, electrical forces, magnetic forces.
 * 4) __Newton__: Force is a quantity that is measured using the standard metric unit known as the **Newton**.
 * [[image:http://www.physicsclassroom.com/Class/newtlaws/u2l2a2.gif width="133" height="27" align="center"]]


 * b) Types of Forces**

S = Survey Q = Question R = Read R = Recite R = Review with dog!
 * 1) What are the different types of forces?
 * 2) What is the different between weight and mass?
 * 1) __Types of forces__:
 * **Applied force** - A force that is applied to an object by a person or another object.
 * **Gravity force** - The force with which the earth (or other massively large object) attracts another object towards itself; weight of the object.
 * **Normal force** - The support force exerted upon an object that is in contact with another stable object.
 * ** Friction force ** -The force exerted by a surface as an object moves across it or 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 rope when it is pulled 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.
 * 1) __Mass vs. weight__: Weight = the force of gravity acting upon an object. Mass = the amount of matter that is contained by the object.


 * c) Drawing Free-Body Diagrams**

S = Survey Q = Question R = Read R = Recite R = Review with dog!
 * 1) What are free-body diagrams?
 * 2) How do you draw free-body diagrams?
 * 1) __Free-body diagrams__: Vector diagrams used to show the relative magnitude and direction of all forces acting upon an object in a given situation.
 * 2) __How to draw FBDs__: The only //rule// for drawing free-body diagrams is to depict all the forces that exist for that object in the given situation. First, identify which forces are present. Then determine the direction in which each force is acting. Last, draw a box and add arrows for each existing force in the appropriate direction; label each force arrow according to its type.


 * d) Determining the Net Force**

S = Survey Q = Question R = Read R = Recite R = Review with dog!
 * 1) What is net force, and how do you determine an object's net force?
 * 1) __Net force__: The vector sum of all the forces that act upon an object. Note = net force takes into account the fact that a force is a vector and two forces of equal magnitude and opposite direction will cancel each other out.

__Lesson 3__: Newton's Second Law of Motion

 * a) Newton's Second Law**

S = Survey Q = Question R = Read R = Recite R = Review with dad.
 * 1) What is Newton's Second Law?
 * 2) What is the equation for Newton's Second Law?
 * 1) __Newton's Second Law__: The acceleration of an object is dependent on the net force acting upon the object and the mass of the object. Acceleration is directly proportional to net force and inversely proportional to mass. As the force increases, the acceleration of the object decreases. As the mass increases, the acceleration of the object decreases.
 * 2) __Equation__:Fnet = m * a


 * b) The Big Misconception**

S = Survey Q = Question R = Read R = Recite R = Review with brother.
 * 1) What is the big misconception?
 * 1) __The big misconception__: The most common misconception is the idea that sustaining motion requires a continued force. Newton's first law of motion declares that a force is __not__ needed to keep an object in motion. An object in motion does not come to a rest position because of the //absence// of a force; rather it is the //presence// of a force (friction) that brings it to a rest position.


 * c) Finding Acceleration**

S = Survey Q = Question R = Read R = Recite R = Review with brother.
 * 1) How does one determine acceleration?
 * 1) __Finding Acceleration__: If the mass (m) and net force (Fnet) or an object are known, then the acceleration is determined by use of the equation a=(Fnet)/m. Three equations that will be useful in determining net force are Fnet = m•a (net force), Fgrav= m•g (gravitational force), and Ffrict = μ•Fnorm (frictional force).


 * d) Finding Individual Forces**

S = Survey Q = Question R = Read R = Recite R = Review with mom.
 * 1) How does one determine the magnitudes of all individual forces if the mass and acceleration of the object are known?
 * 1) __Finding Individual Forces__: If mass (m) and acceleration (a) are known, then the net force (Fnet) can be determined by use of the equation Fnet=ma. If the numerical value and direction of the net force is known, then the value of all individual forces can be determined. The task of determining the values of individual forces involves using the given information in the equations discussed in section b.


 * f) Double Trouble (a.k.a., Two Body Problems)**

S = Survey Q = Question R = Read R = Recite R = Review with dog.
 * 1) What are two-body problems?
 * 2) What is a system analysis?
 * 3) What is an individual object analysis?
 * 1) __Two-body problems__: These problems are characterized by a set of two unknown quantities. Usually, the two unknowns are the acceleration of the two objects and the force transmitted between the two objects.
 * 2) __System analysis__: Analysis where the two objects are considered to be a single object accelerating together as a whole. The mass of the system is the sum of the mass of the two individual objects. If acceleration is involved, the acceleration of the system is the same as that of the individual objects.
 * 3) __Individual object analysis__: One of the two objects is isolated and considered separate and independent. Using a FBD, one can identify and calculate the individual forces acting upon the object. An individual object analysis is usually performed to determine the value of any force which acts between the two objects (ex: contact forces, tension forces).

__Lesson 4__: Newton's Third Law of Motion

 * a) Newton's Third Law**

S = Survey Q = Question R = Read R = Recite R = Review with dog.
 * 1) What is Newton's Third Law?
 * 1) __Newton's Third Law__: For every action, there is an equal and opposite reaction. Forces __always__ come in equal and opposite action-reaction force pairs. The size of the forces on the first object __equals__ the size of the force on the second object. The direction of the force on the first object is __opposite__ to the direction of the force on the second object.


 * b) Identifying Action and Reaction Force Pairs**

S = Survey Q = Question R = Read R = Recite R = Review with dog.
 * 1) How does one identify action and reaction force pairs?
 * 1) __Identifying action and reaction force pairs__: One must identify the 2 interacting objects and make 2 statements describing //who is pushing on whom// and in what direction.

__Lesson 3__ (VECTORS): Forces in Two Dimensions

 * a) Addition of Forces**

S = Survey Q = Question R = Read
 * 1) How are objects affected by forces acting at angles to the horizontal?
 * 2) What is force analysis?

R = Recite R = Talk into the mirror.
 * 1) __Forces at angles__: When a force acting upon an object is at an angle, it has an influence in two dimensions - horizontally and vertically. To use Newton's laws in these situations, vector addition and vector resolution must be applied. The head-to-tail method is commonly used in these situations.
 * 2) __Force analysis__: The goal of a force analysis is to determine the net force and the corresponding acceleration. The net force is the vector sum (resultant) of all forces.


 * b) Resolution of Forces**

S = Survey Q = Question R = Read R = Recite R = Talk into the mirror.
 * 1) How does one resolve a vector into it's components?
 * 1) __Resolving a vector__: Single forces can be resolved into two components: one horizontal and one vertical component. Anytime a force vector is directed at an angle to the horizontal, the trigonometric functions can be used to determine the components of that force vector. The sine function can be used to determine the vertical component of force, and the cosine function can be used to determine the horizontal component of force.


 * c) Equilibrium and Statics**

S = Survey Q = Question R = Read R = Recite R = Talk into the mirror.
 * 1) What is equilibrium?
 * 2) What is static equilibrium?
 * 1) __Equilibrium__: When all forces acting upon an object are balanced. Forces are balanced if the net force = zero (no acceleration). An object at equilibrium is either at rest (and staying at rest) or in motion (and continuing in motion) with constant velocity.
 * 2) __Static equilibrium__: If an object is at rest and in a state of equilibrium.


 * d) Net Force Problems Revisited**

S = Survey Q = Question R = Read R = Recite R = Talk with mom.
 * 1) What is important to know about net force problems?
 * 1) __Net force problems__: There is one peculiarity about problems which combine Newton's second law with force vectors directed at angles. The normal force is not necessarily equal to the gravitational force (as it has been in earlier problems). If there is an acceleration for an object being pulled across a floor, then it is a __horizontal__ acceleration; and thus the only imbalance of force would be in the __horizontal direction__.


 * e) Inclined Planes**

S = Survey Q = Question R = Read R = Recite R = Talk with mom.
 * 1) What are characteristics of objects on inclined planes?
 * 2) Why are inclined plane problems peculiar?
 * 1) __Objects on inclined planes__: There are always __at least two forces__ acting upon any object that is positioned on an inclined plane - the force of gravity and the normal force. The force of gravity (weight) acts in a downward direction and the normal force acts in a direction perpendicular to the surface.
 * 2) __Inclined plane problems__: Analyzing the forces acting upon an object on an inclined plane involves resolving the weight vector into two perpendicular components - one parallel and the other perpendicular to the inclined surface. Because the parallel component of weight causes the object to accelerate, it is the net force. When friction is present, it must be considered when determining the net force.


 * f) Double Trouble in 2 Dimensions (a.k.a., Two Body Problems)**

S = Survey Q = Question R = Read R = Recite R = Talk with mom.
 * 1) How does one analyze two-body problems in which the objects are moving in different directions?
 * 1) __"Different direction" two-body problems__: In problems involving two objects, connecting strings and pulleys are characterized by objects that are moving at the same rate but in different directions. When solving, one must:
 * 1. Select a different reference frame and axes system for each object.
 * 2. Make sure that both objects are accelerating along an axis in the positive direction.
 * 3. Draw a FBD.
 * 4. Apply Newton's laws to each diagram to develop a system of two equations for solving for the 2 unknowns.