Ch4_Sellmanj

=toc Method 4: Lesson 1 11/14= __What is Newton's First Law?__ - It is sometimes called the law of inertia - It is often stated as "an object 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." - Basically, objects will continue to do what they are doing, unless something (a force) changes that course of action (or lack of it) __What are applications of Newton's First Law to real-life scenarios?__ - When you break in a car, coffee continues at the same speed and will go into the windshield when the car slows down, even though the car is stopped - Seat belts provide the unbalanced force that takes a person from a state of motion to a state of rest; if no seat belt was used, when the car stopped suddenly, the person would continue at the same speed and there would be nothing counteracting them. - Blood rushes from head to feet in a descending elevator - Ketchup bottle is turned upside down and then thrusted downward, then abruptly stopped - Headrests are placed in cars to prevent whiplash injuries during rear-end collisions __What ideas did Galileo have relating to the concept inertia?__ - He developed the concept of intertia - He thought that objects stop moving due to the force called friction - He realized that without any friction, the ball could reach the same height that it started from and friction accounted for the differences in the height that it reached - He found that if a ball rolls down and the opposite side is completely horizontal, then the ball will roll with no friction, trying to reach that initial height, but never reaching it, and therefore, never stopping __Why don't forces keep objects moving?__ - It is the presence of forces that stop objects from moving - A force is not needed to keep an object in motion __How does mass act as a measure of the amount of intertia?__ - Mass affects the tendency of an object to resist changes in its state of motion - Mass is solely dependent on the inertia of an object - More massive objects have greater tendencies to resist changes in states of motion __What is the state of motion of an object?__ - The state of motion of an object is defined by its velocity which is the speed with a direction - Inertia is the tendency of an object to resist changes in its state of motion or in its velocity or in its acceleration - The state of motion of an object will not change unless another force acts upon it (an unbalanced force) __What is the difference between balanced and unbalanced forces?__ - When there are two forces acting in opposite directions and have equal magnitude, an object is in equilibrium and these are considered balanced forces, which cause the object to stay in its current state of motion - Unbalanced forces cause acceleration and change the state of motion
 * Lesson A**
 * Lesson B**
 * Lesson C**
 * Lesson D**

=Method 4: Lesson 2 11/15= __What is a force?__ - Forces are pushes or pulls upon objects which result from the object's interaction with another object - Forces only exist as a result of an interaction __What are contact forces? Examples?__ - Contact forces are those that result when two interacting objects are percieved to be physically contacting each other - Examples: frictional forces, tensional forces, normal forces, air resistance forces, applied forces, spring forces __What are action-at-a-distance forces? Examples?__ - These are types of forces that result even when the two interacting objects aren't in physical contact with each other, yet still exert a push or pull despite their physical separation - Examples: gravitational forces, electrical forces, and magnetic forces - Ex. the sun and planets have a gravitational pull on each other despite large separation - Ex. Two magnets can exert a magnetic pull on each other when separated __What is a Newton?__ - This is the unit that forces are measured in; it is abbreviated as N and it is equal to 1 kg*m/s 2 - Newtons aren't a completely accurate depiction of forces because they don't show direction, which is required to explain a force (needing magnitude and direction) __What are the different types of forces and their descriptions?__ - Applied Force (F app ): a force that is applied to an object by a person or another object - Gravity Force/Weight (F grav ): the force that the earth, moon, or other large objects attracts other objects towards itself; this is the weight of an object and on earth, it is directed downwards towards the center of the earth; force of gravity is always equal to the weight of the object ( Fgrav= m x g) - Normal Force (F norm ): the support force exerted upon an object that is in contact with another stable object - Friction Force (F frict ): the force exerted by a surface as an object moves across it or makes an effort to move across it; there are two types, sliding and static; the friction force often opposes motion of the object; maximum amount of friction is (Ffrict = µ • Fnorm) - Air Resistance Force (F air ): special type of frictional force that acts upon objects as they travel through the air; usually opposes motion of an object - Tension Force (F tens ): the force that is transmitted through a string, rope, cable, or wire when it is pulled tight by forces acting from opposite ends - Spring Force (F spring ): exerted by a compressed or stretched string upon an object attached to it; an object that compresses or stretches a string is always acted upon by a force that restores the object to its rest or equilibrium position __How are mass and weight often confused?__ - Mass refers to the amount of matter contained by the object - Weight is the force of gravity acting upon the obect - Mass is measured in kg and will be the same no matter where in the universe the object is located while the weight of an object measured in Newtons will vary according to where in the universe it is __What is the difference between sliding and static 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 __How do you draw a free body diagram?__ - size of the arrow reflects the magnitude of the force - the direction of the arrow shows the direction in which the force is acting - each arrow is labeled to indicate the type of force it is - usually, the object is represented by a box and arrows are drawn from the center in the outward direction __How do you determine the net force?__ - Net force- is the vector sum of all the forces that act upon an object; it is the 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 - Net forces cause an acceleration
 * Lesson A**
 * Lesson B**
 * Sliding Ffrict = μ • Fnorm**
 * Ffrict-static ≤ μfrict-static• Fnorm**
 * Lesson C**
 * Lesson D**

=Method 4: Lesson 3 11/17= __What is Newton's Second Law?__ - pertains to forces that aren't balanced - net force and mass of an object affect acceleration - force is increased, so is acceleration and mass increased, acceleration decreases - "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 - Fnet=m*a - acceleration is directly proportional to net force - use newtons to describe this __What is the Big Misconception?__ - it is hard to understand their meaning and to believe their implications - this requires self-evaluation, critical thinking, and evaluation - most common misconception is that sustaining motion requires a continued force - Newton's laws declare that a net force causes acceleration; acceleration is in same direction as net force - truth is that a force is NOT needed for an object to stay in motion, but the presence of a force like friction will stop motion
 * Lesson A**
 * Lesson B**

= Method 2: Lesson 3 12/5 = - **Addition of Forces** head to tail method the purpose of adding force vectors is to determine the net force acting upon an object an object at equilibrium has balanced forces and is at zero when an object is not in equilibrium, the forces are not balanced, therefore there is a change in motion - **Resolution of Forces** there can be a y component and an x component components show where the force is directed y component shows vertical and x component shows horizontal trigonometry helps determine the components - **Equilibrium and Statics** equilibrium is the state of balanced forces though, not all forces have to be equal net force will be zero object in equilibrium is either at rest or at constant speed static refers to an object at rest - **Inclined Planes** on a tilted surface, object will slide down usually dependent on the angle of the surface to the horizontal with larger tilt, faster speed tilted surface = inclined plane this acceleration is due to unbalanced forces gravity is downward and normal is upward - **Double Trouble in 2 Dimensions (Two Body Problems)** solving for acceleration and the force acting on the objects determine the acceleration to then determine the force between the objects two objects can be looked at as one system to find two equation and solve for the unknowns