Ch4_MalleyJ

Ch4_MalleyJ toc

Lesson 1 Notes: Newton's Laws
Method 4: SQ3R S = Survey (Read the heading of each section and the first sentence of each paragraph. Look at the graphics and pictures to get an idea of what the webpage is about.) Q = Question (Turn the headings into questions to set a purpose for reading, as a prompt for note taking.) R = Read (Read the text to answer your questions and write down the answers in note form.) R = Recite (Cover your answers to the questions and read just the questions, answering them from memory.) R = Review (write a summary of your notes, in paragraph form, or talk it out with your parents (or anyone willing to listen..)

**a.) Newton's First Law**

 * What is Newton's first law of motion?
 * This is the law of inertia, which is often stated as: An object 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.
 * How can Newton's law be applied?
 * For example, if something is being acted on by a force and it speeds up or stops, it's following this rule.

b.) Inertia and Mass

 * What is inertia?
 * Inertia is described as the resistance an object has to a change in its state of motion.
 * What did Galileo have to do with the concept of inertia?
 * He reasoned that moving objects eventually stop because of friction, a force. He did experiments with smooth and rough planes to postulate that if friction could be entirely eliminated, then the object would reach exactly the same height on the incline. He continued this idea by saying that if the opposite incline were elevated at about a 0 degree angle, then the object would go on almost forever in an effect to reach the original height, and it would go on forever if it was actually at a 0 degree angle.
 * Do forces keep objects moving?
 * The answer to this is no. This is because forces are not needed to keep objects in motion. (In some cases, they stop objects from moving).
 * How do you measure the amount of inertia?
 * You can't really measure the amount of inertia, but you can measure mass as a measure of the amount of inertia!! The tendency of an object to resist changes in its state of motion varies with mass, making this possible. Mass is the 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 role does inertia play in velocity?
 * Inertia is the tendency of an object to resist changes in its velocity. An object at rest has 0 velocity.
 * What role does inertia play in acceleration?
 * Inertia is the tendency of an object to resist accelerations. An object at constant velocity has no acceleration.
 * When is there a change in motion?
 * There's only a change in motion if an unbalanced force causes it, otherwise it will move at constant speed in a straight line.

d.) Balanced and Unbalanced Forces

 * What is equilibrium?
 * This is when no unbalanced forces are acting upon a system and thus it remains in its state of motion. An object in this state will not accelerate.
 * What is an unbalanced force?
 * This is a force that causes changes in the state of motion, meaning it causes acceleration.
 * How can you tell whether something is in equilibrium or if there's an unbalanced force?
 * You have to analyze what you're given to determine what forces are acting on the system and in what direction. If two individual forces are of equal magnitude and opposite direction, then the forces are said to be balanced. An object is said to be acted upon by an unbalanced force only when there is an individual force that is not being balanced by a force of equal magnitude and in the opposite direction.

a.) The Meaning of Force

 * What is the meaning of force?
 * A force is a push or pull upon an object resulting from the object's interaction with another object. Whenever there is an //interaction// between two objects, there is a force upon each of the objects. When the interaction ceases, the two objects no longer experience the force. Forces only exist as a result of an interaction.
 * What two groups can forces be grouped in to?
 * Contact forces: those types of forces that result when the two interacting objects are perceived to be physically contacting each other
 * Ex: frictional forces, tensional forces, normal forces, air resistance, and applied forces
 * Action-at-a-distance forces: those types of that 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
 * Ex: gravitational forces
 * What's a Newton?
 * This is a measurement for a force of quantity. Abbreviated by N.

b.) Types of Forces

 * What is applied force?
 * This is a force that is applied to an object by a person or another object.
 * What is gravity force?
 * This is also known as weight. This is the force with which the earth, moon, or other massively large object attracts another object towards itself. This is the weight of the object, by definition.
 * Fgrav = m*g
 * What is normal force?
 * This is the support force exerted upon an object that is in contact with another stable object.
 * What is friction force?
 * This is the force exerted by a surface as an object moves across it or makes an effort to move across it. Two types: sliding and static friction. Usually opposes the motion of an object.
 * What is air resistance force?
 * A special type of frictional force that acts upon objects as they travel through the air. Often observed to oppose the motion of an object. Will frequently be neglected due to its negligible magnitude and the fact that it's nearly impossible to predict its mathematical value.
 * What's tension force?
 * The force that is transmitted through a string, rope, cable, or wire when it is pulled tight by forces acting from opposite ends. Directed along the length of the wire and pulls equally on the objects on the opposite ends of the wire.
 * What is spring force?
 * The force exerted by a compressed or stretched spring upon any object that is attached to it.
 * What's the difference between mass and weight?
 * Mass refers to how much stuff is present in the object, while weight refers to the force with which gravity pulls upon the object.

c.) Drawing Free-Body Disgrams

 * What is a free-body diagram used for?
 * It's used to show the relative magnitude and direction of all forces acting upon an object in a given situation.
 * What's important when drawing an FBD?
 * The system must be removed from its environment. Additionally, the size of the arrow reflects the magnitude and direction of the force. It's then labeled to show what kind of force it is.

d.) Determining Net Force

 * What is a net force?
 * The net force is the vector sum of all the forces that act upon an object. This means that it's the sum of all the forces, taking into account the fact that a force is a vector and two forces equal magnitude and opposite direction will cancel each other out.
 * How can net force be found?
 * The addition of force vectors can be done to determine the net force by summing individual force vectors that are acting upon the objects.

a.) Newton's Second Law

 * What is Newton's second law of motion?
 * Formally stated as: 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. What this means is that the acceleration of an object is dependent upon two variables: the net force acting upon the object, and the mass of the object. The equation for this is: a = F net /m

b.) The Big Misconception

 * What is the big misconception about Newton's second law?
 * It is the idea that sustaining motion requires a continued force, however, this isn't true according to Newton's second law.

a.) Addition of Forces

 * What's very important to keep in mind when drawing the soon-to-be added vectors?
 * You have to watch which way the vector is pointing, as this determines the sign. Keep it tail to tail, usually.

b.) Resolution of Foces

 * What are components?
 * These are the upward/downward and rightward/leftward forces that make up the parts of the vector.
 * How can you solve for these vectors?
 * Use trig functions. SOH CAH TOA is your best friend.

c.) Equilibrium and Statics

 * What does equilibrium mean?
 * When all the forces that act upon an object are balanced, then the object is said to be in a state of equilibrium.
 * When would we say that an object is at 'static equilibrium'?
 * When an object is at rest and in a state of equilibrium, because it's stationary.
 * How can you find the resultant when you have an angle?
 * You can use trigonometric functions to break up the components.

d.) Net Force Problems Revisited

 * How can you solve for all of the forces when there are angles?
 * A situation involving a force at an angle can be simplified by using trig relations to resolve a force into two components. Such a situation can be analyzed like any other situation involving individual forces. The net force can be determined by adding all the forces as vectors and the acceleration can be determined as a ratio of Fnet/mass.

e.) Inclined Planes

 * What usually happens when you place an object on a tilted surface?
 * Usually, it's expected to slide down the surface. Often times, the greater the tilt, the faster the object will slide down it.
 * How can you deal with gravity on an inclined plane?
 * The force of gravity can be resolved into two components. Together, these two components replace the affect of the force of gravity. Once again, you'll deal with trig functions to solve.

f.) Double Trouble in 2 Dimensions (aka, Two Body Problems)

 * What makes problems with two bodies, pulleys, and strings different?
 * These are characterized by objects that are moving (or even accelerating) in different directions. They move or accelerate at the same rate but in different directions. Attention should be given to selecting an axes system such that both object are accelerating along an axis in the positive direction - otherwise watch your signs.

11/15/11

 * No change in motion unless unless an unbalanced force acts on the object... otherwise move at constant speed in a straight line
 * //Inertia is a property//that measures how difficult it is to change an object's motion
 * This is //mass// - measured in Kg
 * Weight is a force, pull of gravity on a mass (N)
 * Acceleration due to gravity is 9.8 m/s/s, so to find weight w=mg (weight equals mass times gravity)
 * Balanced vs unbalanced forces
 * If two forces are equal, then the system is balanced - this is called equilibrium
 * Two types of equilibrium
 * __static__ - at rest, no motion
 * __dynamic__ - constant speed
 * When an unbalanced force acts on an object, it will accelerate in the direction of the unbalanced force
 * If N > w, then acceleration increases upward
 * sigma F - net force (the addition of all of the forces)

11/16/11

 * For the lab, portions of the weight from the ramp are pointing different ways
 * There's a y-component of the weight and an x-component of the weight - to find them, you need to know the angles
 * Acceleration is caused completely by the x-component of weight
 * a = g*sin(theta)
 * y = mx+b
 * Theoretical value
 * a --> x-component of weight