Ch4_ShermanB

CHAPTER 4 toc

Lesson 1 Notes, A-D

1A, Newton's First Law of Motion

 * What is newton's first law?
 * Law of inertia
 * an object at rest will stay in rest, or an object in motion will stay in motion in the same speed and direction unless acted upon by an unbalanced force
 * How is newton's first law of motion applied in everyday life?
 * When a car stops, the passengers remain in motion at the same speed and in the same direction until acted upon by an unbalanced force. This is why seatbelts help save lives in car accidents

1B, Inertia and Mass

 * What is inertia?
 * Inertia is the natural tendency of objects to resist changes in their state of motion
 * How is Galileo related to the concept of inertia?
 * creator of the idea of inertia
 * moving objects stop because of friction
 * experimented with inclined planes
 * ball would roll down one and up the other at around the same height
 * difference between the initial and final heights was because of friction
 * a ball launched at nearly zero degrees would roll almost infinitely to reach the initial height
 * if the final incline wasn't inclined, the ball would roll forever
 * Do forces keep an object in motion?
 * Issac newton discovered that an absence of forces would result in an ever-moving object
 * How are mass and inertia related?
 * Mass is a quantity dependent on inertia
 * tendency to resist changes is based on its mass

1C, State of Motion

 * How are inertia and velocity related?
 * state of motion is defined by its velocity
 * Inertia is the tendency of an object to resist changes in its velocity
 * How are inertia and acceleration related?
 * objects with acceleration are changing their velocity, and thus inertia
 * Inertia is the tendency of an object to resist accelerations

1D, Balanced and Unbalanced Forces

 * What is an unbalanced force?
 * When two or more forces are of different magnitudes or are in non-opposite directions. This leads to a change in motion
 * What is equilibrium?
 * Equilibrium is when two or more forces are of the same magnitude and in opposite directions, resulting in no change of motion
 * Objects with equilibrium will NOT accelerate

2A, The Meaning of Force

 * What is a force
 * a push or pull upon an object resulting from the object's interaction with another object
 * interaction between objects means there's a force acting on them
 * no interaction = no longer experience the force
 * Forces only are a result of interaction
 * What is a contact force?
 * when two interacting objects are physically contacting each other
 * What is an action-at-a-distance force?
 * result when two interacting objects aren't in physical contact, but exert a push or pull despite their physical separation
 * What is a Newton?
 * a measurement of force, it's the amount of force required to give 1kg of mass acceleration of 1m/s/s.
 * kg*m/s^2
 * forces are vectors, a newton must have magnitude and direction

2B, Force and Its Representation

 * What are the types of forces?
 * Applied Force
 * Fapp - applied to an object by a person or another object
 * Gravity
 * (Weight) Fgrav - the weight of an object
 * pull of gravity, directed downwards towards the center of the earth
 * Fgrav = m*g
 * g = 9.8N/Kg(earth)
 * m = mass (in kg)
 * Normal
 * Fn - support force exerted upon an object that is in contact with another stable object
 * sometimes a normal force is is exerted horizontally between two objects in contact
 * Friction
 * Ffrict - force exerted by a surface as an object moves across it or makes an effort to move across it
 * often opposes the object
 * Two types - static and sliding
 * amount depends on the nature of the surface
 * max amount of friction calculated by -
 * Ffrict = µ • Fnorn
 * Air Resistance Force
 * Fair - acts upon an object as it travels through the earth
 * observed to oppose the motion of an object
 * frequently neglected because of its miniscule magnitude, also difficult to find a value
 * Tension Force
 * transmitted through a string, rope, cable, or wire when it's pulled tight by forces acting from opposite ends
 * directed along the length of a wire and pulls equally on the objects on opposite ends of the wire
 * Spring Force
 * Fspring - exerted by a compressed or stretched spring upon an object that is attached to it
 * object that compresses or stretches a spring is always acted upon by a force that restores the object to its rest of equilibrium position
 * Most springs - magnitude is directly proportional to the amount of stretch or compression of a spring
 * How are mass and weight confused?
 * Weight = Force of gravity acting upon an object
 * dependent on the "g" value, gravitational field stregnth
 * changes depending on planet and certain parts of earth
 * Mass = amount of matter that is contained by the object
 * Mass is the same wherever in the universe the object is, weight changes based on the amount of gravity

2C, Drawing Free Body Diagrams

 * What is a free body diagram?
 * A diagram used to show the relative magnitude and direction of all forces acting upon an object in a given situation
 * Form of vector diagrams
 * What are the characteristics of a free body diagram?
 * The size of the arrow representing a force reflects the magnitude of the force
 * Direction of the arrow represents the direction of the force
 * each arrow must be labeled correctly
 * Object represented by a box with arrows from the center going outward in the direction that the force is acting
 * The object can have many or few forces acting on it

2D, Determining the Net Force

 * What is a net force?
 * the vector sum of all the forces that are acting on an object
 * taking into account the magnitude and direction of the vectors
 * it can cause acceleration
 * How do we determine the net force of an object?
 * Unbalanced forces are forces that don't become completely canceled out by other forces
 * If all the forces aren't equal, the object will move as the forces acting on it are unbalanced
 * Adding and subtracting are the same as with vectors

3A, Newton's Second Law

 * What is Newton's second law of motion?
 * 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
 * a=Fnet/m
 * ^ same as Fnet=m*a
 * specifically the net force
 * 1 Netwon = 1kg*m/s^2
 * What is equilibrium?
 * The condition in which all forces are balanced

3B, The Big Misconception

 * What is the big misconception?
 * not the ability to remember or recite the first law, or use the second law in questions, but rather to understand their meaning and implications
 * physics students tend to have a certain set of beliefs
 * fixing requires self reflection, critical thinking, and evaluation
 * people think that keeping an object in motion requires a force, this isn't so


 * Do I hold this misconception?
 * objects continue infinitely at zero degrees if there is no friction and no forces opposing their motion