Ch4_Sekiko

toc =Physics Classroom Notes=

A: Newton's First Law
Question: What is Newton's first law of motion, and how does it apply to physics? Question: How is this relevant to our everyday lives? Summary: Newton's first law of motion, or the law of inertia, basically states that things will keep on doing what they are doing. Stationary objects will stay at rest, while objects in motion will stay in motion. However, an unbalanced force can make these objects change. We see examples of this everyday, like when riding in a car, in an elevator, and when using ketchup (making the ketchup go to the "nozzle" by thrusting it down and then stopping it quickly).
 * aka Law of Inertia
 * An object at rest stays at rest and an object in motion stays in motion with the same speed and direction unless acted upon by an unbalanced force.
 * There are two parts to this statement - each predicts the behavior of an object either moving or stationary.
 * Things keep on doing what they are doing
 * For example, cars tend to illustrate many of these concepts.
 * Seatbelts are unbalanced forces that prevent people (who are in motion) from flying out of the windshield.

B: Inertia and Mass
What did Galileo do to further our understanding of inertia? How did Newton expand upon Galileo's discoveries How is inertia measured? Summary: Galileo first introduced the concept of inertia, though it wasn't until Newton that it was expanded upon and made into a legitimate scientific concept. Newton reasoned, based on Galileo's experiments, that it wasn't the absence of a force that caused an object to slow down, it was the presence of one, specifically friction. Friction slows down objects and eventually causes them to go to rest. Inertia, like other quantities, can be measured. The more mass an object has, the less susceptible it is to changes in motion.
 * Inertia - the resistance an object has to a change in its state of motion
 * Galileo reasoned that friction eventually stopped motion
 * Through a series of experiments with planes and balls, he was able to deduce that the ball would roll endlessly if not for friction in order to return to the original height it was dropped at.
 * The presence of friction bring the book to rest, not the absence of force.
 * Inertia is dependent on the mass of an object
 * More inertia = more mass.
 * Bigger objects tend to resist changes in its state of motion better

C: State of Motion
What does the phrase "state of motion" mean? Summary: The state of motion of an object is its velocity. At 0 m/s, it is at rest. At anything else, it is in constant speed. Thus, inertia can be defined as the tendency of an object to resist changes in its velocity. Because changes in velocity are accelerations, we can also say that inertia is the tendency of an object to resist accelerations.
 * State of motion = velocity
 * Object that doesn't change its velocity has an acceleration of 0.
 * Thus, Inertia can be the tendency of an object to resist accelerations.

D: Balanced and Unbalanced Forces
What is the difference between balanced and unbalanced forces? Summary: Balanced forces are those that are equal in magnitude but in opposite directions. They will cancel each other out and not cause any motion because they are balanced. However, add any unbalanced force, and the object will move and change its state of motion. This is because there is nothing to counteract this force.
 * Forces that are equal in magnitude and in opposite directions balance each other out, and thus, are at equilibrium.
 * We only care about the current situation of an object, not the history. (remember, newton said that what caused objects to slow down wasn't the absence of a force, but the presence.)
 * Friction will slow down things if not balanced by something else.

A: The Meaning of Force
What are forces and how are the characterized? How are forces measured? Summary: Forces are pushes or pulls from the interaction of two objects. They do not necessarily have to be touching each other, but can be. Those that do are called contact forces, while those that don't are called action-at-a-distance forces. They are vector quantities, and thus need direction as well as magnitude. Their magnitude is represented by Newtons.
 * Forces are pushes or pulls from an object's interaction with another one.
 * They only exist as a product from the interaction
 * Forces can be characterized into two categories: contact forces, and action-at-a-distance
 * Contact ones are when two objects are in contanct with each other
 * Action at a distance are when two objects are not in contact, yet are able to exert a push or pull (like magnetism)
 * Measured in Newtons (N)
 * Forces are vector quantities, and, such need direction as well as magnitude.

B: Types of Forces
How are forces differentiated from each other? What's the difference between Mass and Weight? How are sliding and static friction different? Summary: There are many different types of forces, though they can be categorized into basic groups. They are contact forces and action-at-a-distance forces. However, within these groups, there are many other specific forces. In the contact forces group, there are friction forces, tension forces, normal forces, air resistance forces, applied forces, and spring forces. In the aaad (action at a distance) forces, there are gravitational forces, electrical forces, and magnetic. In order to understand these forces, however, we need to understand the difference between mass and weight. Mass is how much stuff is in something, while weight is the gravitational pull on that stuff. Friction has two types of forces that generally try to prevent or slow down motion.
 * Applied forces are just what they say. They are forced applied to one thing by something else
 * Gravity is the force in which large object (planets) attract objects towards themselves. The force of gravity is equal to the weight (Fgravity = M x g)
 * Normal force is the support force that is exerted upon an object that touches another.
 * There are two types of friction - static and sliding. Static friction is what keeps something stationary, while sliding friction opposes the motion of an object.
 * Air resistance force is the friction that an object receive as they travel through the air and is opposite the motion.
 * Tension is the force transmitted through string, rope and the like.
 * Spring force is the force exerted by a spring (compressed or stretched)
 * Mass is the amount of stuff in something, whereas weight is the force of gravity on an object
 * Sliding - when an object slides across a surface
 * Sliding Friction = u (measure of relative adhesion) x normal force
 * Static friction is when two surfaces are at rest relative to one another and a force is needed to put it into motion relative to the other object. It prevents motion.
 * Static friction <_ coefficient of static friction (u) x normal force

C: Drawing Free-Body Diagrams
How do you draw free-body diagrams? Summary: Free body diagrams are useful in isolating an object from its system in order to figure out what forces are acting on it. They show each force and use size and direction to show the magnitude and direction.
 * free body diagrams are a vector diagram that shows the relative magnitude and direction of all of the forces acting on an object.
 * size = magnitude, direction = direction, and each arrow must be labeled.

D: Determining the Net Force
What is net force and how do you determine it? Summary: Net force is the sum of all of the vector forces on an object. You find it by adding.
 * Net force is the vector sum of all forces acting on an object
 * Vectors can cancel out only when they are in opposite directions
 * Just add the vectors to find the net force

A: Newton's Second Law
What is Newton's Second Law? Is it similar to the first one? Summary: Newton's second law describes the behavior of objects when the forces are not balanced. Acceleration is due to two variables, mas and net force. However, it is related to these two variables in different ways. It is directly proportional to the net force, but inversely proportional to the mass. Thus, the equation is A = Fnet/m
 * Pertains to behavior of object where forces are not balanced.
 * Acceleration is due to two variables, net force, and the mass
 * Acceleration is directly proportional to the net force, and inversely upon the mass
 * A = Fnet / m, or Fnet = m *a
 * It is related, but not similar. It expands upon the first to include when forces are not balanced. '

B: The Big Misconception
What is the big misconception, and what makes it hard to understand? Summary: Forces do not cause motion, but rather, accelerations. This means that even if there are only vertical forces, there can still be an object in motion. What stops motion, as said in newton's first law, is presence of friction, not the absence of an applied force on the object.
 * People believe that sustaining motion requires a continued force.
 * An object can be moving even if there are only vertical forces.
 * Forces cause acceleration, not motion.
 * The presence of a force stops motion, not the absence

D: Net Force Problems Revisited
What is new about these types of net force problems? How do you solve them? Summary: Use trigonometry to break an angled force into its components. These components will act as separate forces, and must be taken into account when doing calculations for other forces, especially gravity.
 * They have forces that are at a different angle
 * The normal force is not equal to the force of gravity
 * The angled forces + normal force = force of gravity
 * Break down the force into its two components and treat those as two forces.
 * After you do this, just solve in the normal fashion

=Activities / Labs=