Ch4_HallR

toc =Lesson 1: Newton's First Law of Motion=

11/14/11: A-D Summary
__A: Newton's First Law__ What is Newton's First Law of Motion?
 * Also known as the law of inertia
 * An object at rest will stay at rest and an object in motion stays in motion at the same velocity and in the same direction unless acted upon by an UNBALANCED force.
 * [[image:http://www.physicsclassroom.com/Class/newtlaws/u2l1a1.gif width="243" height="184"]]
 * No change in motion unless an unbalanced force acts on the object; otherwise an object will move at constant speed in a straight line.

__B: Inertia and Mass__ What is Inertia?
 * Inertia is the tendency an object has to resist changes in its state of motion.
 * The reason objects stop is usually due to friction, not the absence of a force.
 * A force is __not__ needed to keep an object in motion.
 * In the absence of a force of friction, most objects would continue in motion with the same speed and direction.
 * All objects resist changes in their state of motion; all objects have inertia.
 * Inertia changes with mass.
 * Mass is that quantity that is __solely__ dependent upon the inertia of an object.
 * The more inertia that an object has, the more mass that it has. A more massive object has a greater tendency to resist changes in its state of motion.

__C: State of Motion__ What is state of motion?
 * The state of motion of an object is its velocity (speed in a direction)
 * Therefore, inertia is the tendency an object has to resist changes in its velocity.
 * OR, an object's tendency to resist changes in acceleration
 * This is because an object with a constant velocity has an acceleration of 0 m/s/s, which will only change if it is acted upon by an unbalanced force.
 * Inertia is a PROPERTY that measures how difficult it is to change the object's motion.
 * This is MASS - measured in grams/kilograms (g/Kg)
 * Weight is a force, the pull of gravity on a mass - measured in newtons (N)
 * g = 9.8 m/s/s
 * Weight = Mass x g

__D: Balanced and Unbalanced Forces__ What is an unbalanced force?
 * Equilibrium: When two forces balance each other due to having equal magnitude but going in opposite directions.
 * Therefore, opposite velocities (one's is positive, the other's is negative)
 * If the forces acting on an object are in equilibrium, an object maintains its current state of motion.
 * Most objects sliding horizontally slow down because there is no force balancing friction.
 * Since this force is unbalanced, the object changes its state of motion.
 * Unbalanced forces cause accelerations.
 * Two types of Equilibrium = Static and Dynamic
 * Static Equilibrium is when the object is at rest.
 * Dynamic Equilibrium is when the object is at constant speed.
 * 2nd Law: When an Unbalanced for acts on an object, it will accelerate in the direction of the unbalanced force.
 * Net force: addition of all of the forces acting on an object.

=Lesson 2: Force and Its Representation=

11/15/11: A-D Summary
__A: The Meaning of Force__ What is a force? What is a contact force? What are action-at-a-distance forces? What is a Newton?
 * A force is a push or pull upon an object due to the objects interaction with another object.
 * When two objects interact, there is a force upon each of the two objects.
 * When the interaction ends, the objects no longer are acted upon by the force.
 * Forces can be categorized into two groups: contact forces and forces that result from actions-at-a-distance.
 * Contact forces are forces that result from two interacting objects physically contact each other.
 * Examples: Frictional forces, tensional forces, normal forces, air resistance forces, applied forces, and spring forces.
 * They are forces that result from two objects that are not in physical contact with each other, yet exert a push or pull from a distance.
 * Examples: gravitational forces, electric forces, and magnetic forces.
 * A Newton is the standard metric unit used to measure the quantity of force.
 * Abbreviated as 'N.'
 * One Newton is the amount of force required to give a 1-kg mass an acceleration of 1 m/s/s.
 * [[image:http://www.physicsclassroom.com/Class/newtlaws/u2l2a2.gif]]
 * Force is a vector quantity, so it has both magnitude and direction.
 * Forces are commonly shown using free-body diagrams, using arrows for forces.

__B: Types of Forces__ What are the types of forces? What is an Applied Force?
 * **Contact Forces** || **Action-at-a-Distance Forces** ||
 * Frictional Force || Gravitational Force ||
 * Tension Force || Electrical Force ||
 * Normal Force || Magnetic Force ||
 * Air Resistance Force ||  ||
 * Applied Force ||  ||
 * Spring Force ||
 * An applied force is a force that is applied to an object by another object.
 * Abbreviation: Fapp

What is a Gravity Force? > Fgrav = m * g where g = 9.8 N/kg (on Earth) > and m = mass (in kg)
 * Also known as weight.
 * The force of gravity is the force with which a massively large object attracts another object towards itself.
 * All objects upon earth experience a force of gravity that is directed "downward" towards the center of the earth.
 * The force of gravity on earth is always equal to the weight of the object as found by the equation:
 * Abbreviation: Fgrav

What is a Normal Force?
 * A normal force is the support force exerted on an object that is in contact with another object.
 * Abbreviation: Fnorm

What is a Friction Force? > Ffrict = µ • Fnorm
 * A friction force is the force exerted by a surface as an object moves across it or makes an effort to move across it.
 * There are at least two types of friction force - sliding and static friction.
 * A friction force usually opposes the motion of an object.
 * It is the result of two surfaces being pressed together closely, causing intermolecular attractive forces between molecules of different surfaces.
 * Therefore, friction depends upon the nature of the two surfaces and the degree to which they are pressed together.
 * The maximum amount of friction force that a surface can exert upon an object can be found by:
 * Abbreviation: Ffrict

What is an Air Resistance Force?
 * Air resistance is a special type of frictional force that acts upon objects that travel through the air.
 * Like friction, air resistance often opposes the motion of an object.
 * This force is usually neglected due to its negligible magnitude.
 * It is most noticeable for objects that travel at high speeds or have large surface areas.
 * Abbreviation: Fair

What is a Tension Force?
 * A tension force is the force that is transmitted through a string, rope, cable or wire when it is pulled by forces acting from opposite ends.
 * A tension force is directed along the length of the wire and pulls equally on the objects on the opposite ends of the wire.
 * Abbreviation: Ftens

What is a Spring Force?
 * A spring force is the force exerted by a compressed or stretched spring upon any object that is attached to it.
 * An object that compresses or stretches a spring is always acted upon by a force that restores the object to its rest or equilibrium position.
 * For most springs, the magnitude of the force is directly proportional to the amount of stretch or compression of the spring.
 * Abbreviation: Fspring

What are the differences between mass and weight?
 * The force of gravity acting upon an object is the weightof the object.
 * The massof an object refers to the amount of matter that is contained by the object
 * Mass is related to how much 'stuff' is in the object, and weight is related to the pull of the Earth (or another planet) upon that //'//stuff.'
 * Mass is never altered by location, the pull of gravity, speed or even the existence of other forces.
 * However, weight (measured in Newtons) will vary according to where in the universe the object is.
 * Weight depends upon which planet is exerting the force and the distance the object is from the planet.
 * Weight, being equivalent to the force of gravity, is dependent upon the value of g, or the gravitational field strength.
 * On Earth's surface, gis 9.8 N/kg.
 * G value is inversely proportional to the distance from the center of the planet.

What are the differences between sliding and static friction? > **Sliding Ffrict = μ • Fnorm** > **Ffrict-static ≤ μfrict-static• Fnorm** The symbol **μfrict-static** represents the coefficient of static friction between the two surfaces.
 * Friction is the force exerted by a surface as an object moves across it or makes an effort to move across it.
 * There are 2 types - static friction and sliding friction.
 * Sliding friction is when an object slides across a surface.
 * Sliding friction forces can be calculated from knowledge of the coefficient of friction and the normal force exerted on the object by the surface it is sliding across. The formula is:
 * The symbol [[image:http://www.physicsclassroom.com/Class/newtlaws/redmusliding.gif width="41" height="11" align="middle"]] represents the coefficient of sliding friction between the two surfaces.
 * The coefficient value is dependent on the nature of the surfaces that are in contact with each other.
 * For most surface combinations, the friction coefficients show little dependence on other variables such as area of contact, temperature, etc.
 * The values of **μ** provide a measure of the relative amount of adhesion or attraction of the two surfaces for each other.
 * The more that surface molecules tend to attract to each other, the greater the coefficient values and the greater the friction force.
 * Static friction is 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.
 * The amount of static friction resulting from the adhesion of any two surfaces has an upper limit.
 * This relationship is often expressed as follows:
 * Like the coefficient of sliding friction, this coefficient is dependent upon the types of surfaces that are attempting to move across each other.
 * Usually, values of static friction coefficients are greater than the values of sliding friction coefficients for the same two surfaces.
 * Therefore, it usually takes more force to set an object into motion than it does to maintain the motion once it has been started.

__C: Drawing Free-Body Diagrams__ What is a free-body diagram?
 * Free-body diagrams are diagrams used to show the relative magnitude and direction of all forces acting upon an object.
 * A free-body diagram is a special example of a vector diagram
 * The size of the arrow in a free-body diagram reflects the magnitude of the force, and the direction of the arrow shows the direction that the force is acting.
 * Each force arrow in the diagram is labeled to indicate the exact type of force.
 * Usually in a free-body diagram, the object is represented by a box, and the force arrow is drawn from from the center of the box outward in the direction that the force is acting.
 * [[image:http://www.physicsclassroom.com/Class/newtlaws/u2l2c1.gif]]
 * The only rule for drawing free-body diagrams is to depict all the forces that exist for that object in the given situation.

__D: Determining the Net Force__ What is net force?
 * The net force is the vector sum of all the forces, taking into account the fact that a force is a vector and two forces of equal magnitude and opposite direction will cancel each other out.
 * A downward vector will provide a partial or full cancellation of an upward vector, and a leftward vector will provide a partial or full cancellation of a rightward vector.
 * The addition of force vectors can be done in the same manner in order to determine the net force (i.e., the vector sum of all the individual forces).
 * A net force (unbalanced force) causes acceleration

=Lesson 3: Newton's Second Law of Motion=

11/17/11: A & B Summary
__A: Newton's Second Law__ What is Newton's Second Law of Motion?
 * Regards the behavior of objects for which all existing forces are unbalanced.
 * Says hat the acceleration of an object is dependent upon two variables - the net force acting on the object and the mass of the object.
 * The acceleration of an object depends directly upon the net force acting on the object, and inversely on the mass of the object.
 * If the force acting upon an object increases, the acceleration of the object increases.
 * If the mass of an object increases, the acceleration of the object decreases.
 * [[image:http://www.physicsclassroom.com/Class/newtlaws/u2l3a2.gif]]
 * //The acceleration of an object as produced by a net force is directly proportional to the magnitude of the net force, in the same direction as the net force, and inversely proportional to the mass of the object.//
 * This verbal statement can be expressed in equation form as follows:
 * **a = Fnet / m**
 * or
 * ===** **Fnet = m * a** **===
 * A unit of force is equal to a unit of mass times a unit of acceleration.
 * [[image:http://www.physicsclassroom.com/Class/newtlaws/u2l2a2.gif width="133" height="27" align="center"]]
 * The definition of the standard metric unit of force is stated by the above equation.
 * One Newton is defined as the amount of force required to give a 1-kg mass and acceleration of 1 m/s/s
 * Doubling the net force results in doubling the acceleration (if mass is held constant).
 * Also, halving the net force results in halving the acceleration (if mass is held constant).
 * Doubling of the mass results in halving the acceleration (if force is held constant).
 * Also, halving the mass results in doubling the acceleration (if force is held constant).
 * Double, triple or quadruple the net force, and the acceleration will do the same.
 * Whatever alteration is made of the mass, the opposite/inverse change will occur with the acceleration.
 * Double, triple or quadruple the mass, and the acceleration will be one-half, one-third or one-fourth its original value.

__B: The Big Misconception__
 * The most common misconception is the idea that sustaining motion requires a continued force.
 * A net force (an unbalanced force) causes an acceleration; the acceleration is in the same direction as the net force.
 * A force is __not__ needed to keep an object in motion.
 * An object in motion does not slow to rest because of an absence of a force, but instead the presence of a force, friction.
 * Without friction, the object would keep moving in the same direction at the same velocity.