Ch4_GirginL

= Newton's Laws - Lesson 1: A-D = toc November 14, 2011

Newton's First Law- What is Newton's First law?
 * an object at rest stays at rest
 * an object in motion stays in motion
 * unless acted upon by an unbalanced force
 * or state of motion is changed
 * the behavior of all objects is described as them tending to keep on doing what they are doing

Everyday Application of Newton's First Law What are some everyday applications of Newton's First Law?
 * a coffee in a coffee cup in your car
 * if the car accelerates from rest, the coffee wants to stay at rest
 * while the car accelerates forward, the coffee may spill
 * when braking from a state of motion, the coffee continues forward with the same speed and same direction

Summary: Newton's First law of motion deals with how the motion of an object is described. If an object starts out at rest, and no unbalanced forces act upon it, the object will stay at rest. An example of this can be seen with a pebble on the ground. If the pebble is not kicked or blown from the wind, the pebble will stay in the same position at rest. Furthermore, if an object is in motion, the object will stay in motion. This can be seen with the example of a coffee placed in a coffee cup in a car. If the driver hits the brakes of the car from 30 mph to 0 mph, the coffee will go forward with the same speed and direction. If an object does not meet any unbalanced forces, it will continue to "keep doing what it is doing".

Inertia and Mass- What are inertia and mass?
 * the tendency for objects to stay in their state of motion is inertia

Galileo and the concept of inertia- What was Galileo's perception on inertia?
 * moving objects eventually stop moving due to friction
 * any difference between initial and final heights was due to friction

His experiment
 * he placed two planes facing each other and let a ball go down one plane
 * it went down the first plane and went up to approximately the same height from where it was dropped
 * had there been no friction, the ball would have been in the exact same height as it was dropped from
 * he reasoned that if one plane had no slope, the ball would stay in motion forever, if there was no friction

Forces Don't Keep Objects Moving- What do forces do?
 * the force of friction brings the object to rest
 * foce doesn't keep an object moving

Mass as a Measure of the Amount of Inertia- What role does mass play in the measure of the amount of inertia?
 * The tendency of an object to resist changes in state of motion varies with mass
 * the more inertia an object has, the more mass
 * a more massive object has a greater tendency to resist changes in its state of motion

State of Motion- What are states 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
 * an object at rest will continue to have 0 velocity

Summary: The state of motion of an object will not change unless acted by unbalanced forces, but inertia will also play a role in the objects velocity. Inertia is the tendency of an object to continue with constant velocity. An object at rest will continue to have 0 velocity and an object going east at 40 mph will continue to go east at 40 mph forever unless acted by an unbalanced force.

Balanced and Unbalanced Forces- What are balanced and unbalanced forces?

= Newton's Laws - Lesson 2: A-D = November 16, 2011

The Meaning of Force- What is the meaning of force? Contact Forces- What are contact forces? Action-at-a-distance forces- What are at-a-distance-forces?
 * a force is a push or pull upon an object resulting from the object's interaction with another object.
 * when the interaction stops, the two objects no longer experience the force
 * There are two broad categories of forces
 * contact froces
 * forces resulting from action-at-a-distance
 * types of forces that result when the two interacting objects are perceived to be physically contacting each other.
 * examples include:
 * frictional forces
 * tensional forces
 * normal forces
 * air resistance forces
 * applied forces
 * types of forces 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
 * examples include:Force is quantity that is measured using the unit known as Newton
 * electric forces
 * magnetic forces
 * gravitational forces
 * 1 Newton = 1 kg x m/s/s
 * force is a vector quantity
 * it has both magnitude and direction
 * force is represented with arrows because it is a vector that has a direction
 * force is represented with arrows because it is a vector that has a direction

Description of Force- What is the description of Applied force? What is the description of Gravity Force? What is the description of Friction Force? What is the description of Air Resistance Force? What is the description of Tension Force? What is the description of Spring Force?
 * it is a force that is applied to an objet by a person or another object
 * an example would be someone pushing a desk across the room
 * it is the force with which the earth, moon, or other massively large object attracts another object towards itself
 * definition - the weight of an object
 * all objects on earth experience a force of gravity that is directed downward to the center of the earth
 * it is the force exerted by a surface as an object moves across it or makes an effort to move across it
 * an example would be a book sliding across the surface of a desk, then the desk exerting a friction force in the opposite direction of its motion
 * friction depends upon the nature of the two surfaces and upon the degrees to which they are pressed together
 * a special type of frictional force that acts upon objects as they travel through the air
 * this force will frequently be neglected due to its negligible magnitude
 * the force that is transmitted through a string, rope, cable or wire when it is pulled tight by forces acting from opposite ends.
 * the force is directed along the length of the wire and pulls equally on the objects on the opposite ends of the wire
 * the force exerted by a compressed or stretched spring upon any object that is attached to it
 * the magnitude of the force is directly proportional to the amount of stretch or compression of the spring

Confusion of Mass and Weight- What is the difference of mass and weight?
 * mass is the amount of material inside an object
 * weight the the amount of force or pull of an object
 * due to gravity

Sliding versus Static Friction- What is 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 force exists on one of the objects to set it into motion relative to the other object.

Free Body Diagrams
 * They are used to show the relative magnitude and direction of all forces acting upon an object in a given situation.


 * The size of the arrow in a free-body diagram reflects the magnitude of the force.
 * The direction shows the direction that the force is acting.
 * Each force arrow in the diagram is labeled to indicate the exact type of force.

Determining the Net Force
 * If either all the vertical forces do not cancel each other or the horizontal forces, than an unbalanced force exists

= Newton's Laws - Lesson 3: A&B = November 17, 2011

What is Newton's Second Law?
 * It pertains to the behavior of objects for which all existing forces are not balanced.
 * The acceleration of an object is dependent upon two variables
 * the net force
 * mass of the object
 * The acceleration of an object depends directly upon the net force and inversely upon th emass[[image:http://www.physicsclassroom.com/Class/newtlaws/u2l3a2.gif]]
 * This is expressed in the following equation: a = Fnet / m
 * This can be rearranged to the form: Fnet = m * a

What are some common misconceptions pertaining to Newton's Second Law?
 * The idea that sustaining motion requires a continued force
 * No force is required to keep a horizontally moving object in motion