Ch4_GreensteinJ

toc =Notes 11/9=


 * Forces**
 * Act __on__ a system __by__the environment
 * System- object you are examining
 * Environment- everything outside the system
 * We don't care what the system does __to__ the environment or what happens __inside__ the system
 * Cannot be __carried__ or __transferred (stored)__
 * Non-conservative
 * Represented with an arrow (vector)
 * Units are Newtons (N)
 * Equivalent to kg m/s 2
 * Many types of forces
 * Mechanical forces
 * Name || Symbol || Description || Direction ||
 * Weight (gravitational) || w, F g || Pull of gravity on a mass || Down towards center of Earth ||
 * Normal || N, F N || Push, acts when 2 surfaces are in contact || Perpendicular to surfaces & through the system ||
 * Tension || T, F T || Pull, by a rope or chain || Along the rope, away from the system ||
 * Friction || f, F f || 2 surfaces slide past each other || Parallel to the surfaces, opposite motion ||
 * Free Body Diagram**
 * 1) Separate system from environment
 * 2) Draw arrows to represent all forces acting on system
 * 3) Label each arrow with a unique symbol

=Physics Classroom 1a=


 * 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]


 * What are everyday applications of Newton's law of inertia?**
 * Coffee spilling when you accelerate
 * Coffee is at rest while car suddenly starts moving
 * Flying forward in a car crash
 * Your body is still moving while the car stops

=Physics Classroom 1b=


 * What was Galileo's take on the concept of inertia?**
 * Developed the concept
 * Postulated that if you eliminate friction, a rolled ball would continue rolling down an incline and back up to its original height
 * If there was no incline, the ball would continue in motion trying to achieve its original height


 * What are some misconceptions about force and motion?**
 * A force is NOT required to keep an object moving
 * Newton's first law states a force is not needed to keep an object in motion
 * a force (such as friction) can stop motion


 * How are mass and inertia related?**
 * An object resisting movement is inertia
 * Some objects resist more than others
 * Mass is that quantity that is __solely__ dependent upon the inertia of an object
 * More mass = more resistance = more inertia

=Physics Classroom 1c=


 * What is meant by a state of motion?**
 * The state of motion of an object is defined by its [|velocity]
 * **Inertia: tendency of an object to resist changes in its velocity.**
 * Objects resist changes in their velocity.
 * **Inertia: tendency of an object to resist accelerations.**

=Physics Classroom 1d=


 * What are balanced and unbalanced forces?**
 * 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
 * Balanced force- when forces are in equilibrium and do not affect state of motion
 * Unbalanced force- a force which is not in equilibrium and changes an object's state of motion



= Physics Classroom 2a =
 * What is a force?
 * A **force** is a push or pull upon an object resulting from the object's //interaction //with another object
 * Contact
 * Friction
 * Tension
 * Normal
 * Air resistance
 * Applied
 * Spring
 * At-a-distance
 * Gravitational
 * Electrical
 * Magnetic

= Physics Classroom 2b =
 * What is the difference between Weight vs. Mass
 * Weight- force of gravity on an object
 * Mass- amount of matter in object

= Physics Classroom 2c =
 * 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
 * The size of the arrow = the magnitude of the force
 * The direction of the arrow = direction that the force is acting
 * Label = the exact type of force.
 * [[image:http://www.physicsclassroom.com/Class/newtlaws/u2l2c1.gif width="198" height="184"]]

= Physics Classroom 2d =
 * How do you solve for net force?
 * Net force is caused by unbalanced force
 * One force is stronger than another opposite one
 * The vector sum of all the forces = net force
 * [[image:http://www.physicsclassroom.com/Class/newtlaws/u2l2d3.gif width="456" height="156" align="bottom"]]

= Physics Classroom 3a =


 * What is Newton's 2nd Law?
 * The acceleration of an object is dependent upon two variables - the [|net force] acting upon the object and the mass of the object
 * [[image:http://www.physicsclassroom.com/Class/newtlaws/u2l3a2.gif width="227" height="179" align="bottom"]]
 * a = Fnet / m
 * Fnet = ma

= Physics Classroom 3b =


 * What is a misconception with regard to Newton's laws?
 * Sustaining motion does NOT require continued force
 * [[image:http://www.physicsclassroom.com/Class/newtlaws/u2l1b1.gif width="319" height="109" align="bottom"]]

= Notes 11/17 =

**Fnet = ma** net force = mass * acceleration

=Notes 11/18=


 * What is a?
 * a = Fnet / m
 * Fnet = force causing system to accelerate
 * m = total mass that is acceleration

=Notes 12/5=


 * **Friction**- force (N)
 * Depends on normal force of surface & type of surface
 * NOT surface area or speed
 * Coefficient of static friction µ s
 * Not moving, friction keeps object from sliding
 * For any 2 substances, static friction is greater than kinetic
 * Coefficient of kinetic friction µ k
 * motion sliding
 * 0 < µ < 1
 * 0 is frictionless
 * 1 is rougher
 * can be above 1
 * f = µN
 * friction equals mu times normal
 * NO units!

Steps to Solve:


 * 1) Draw a picture
 * 2) Label all known information
 * 3) Note the unknown that you are solving for
 * 4) Draw a motion diagram
 * 5) Draw a free body diagram, showing all forces
 * 6) Write out the equations for Newton's 2nd Law (Fnet = ma)
 * 7) Substitute in the specific forces on the x-axis and then do the same for the y-axis equation
 * 8) Solve for weight, showing the equation w=mg and numbers plugged in
 * 9) Solve for the normal force from the surface along which the system is sliding
 * 10) Solve for friction force with Fk = µN
 * 11) Use kinematics to solve for acceleration
 * 12) Use x-axis equation to solve for other force