(1)+Newton's+First+Law+and+Linear+Motion

PAGE EDITORS: Leti Pfeffer, Bertha Chen, Elaine Ramsay


 * Due Date: 11/02/09 (Monday)**

Introduction to Physics:

The success and credibility of science are anchored in the willingness of scientists to: 1- Expose their ideas and results to independent testing and replication by others 2- Abandon or modify previously accepted conclusions when confronted with more complete or reliable experimental data.

The fundamental difference between beliefs and the scientific method: 1- Scientific method has to be fallible; has to be proven wrong in some way 2- Beliefs explain how and why things happen a. Science doesn’t go into this

1- **Hypothesis** – a testable statement accounting for a set of observations 2- **Theory** – a well-supported and well-tested hypothesis or set of hypotheses 3- **Law** – a conclusion confined to such an extent that it would be reasonable to offer provisional agreement

1- Position of “tic” marks should be evenly spaced on each axis 2- Label axis with units 3- Independent variable on the x-axis and dependent on y-axis 4- Use “x”s for data points 5- Singular descriptive title 6- Best fit line - equal # of point above and below line.
 * Important Notes When Graphing:**

__**Physical** **Quality**__ __**Dimension**__ __**Basic** **Unit**__ 1 length (ft., mi., light-year) 1 [L] 1 m (meter) 2 mass (pound, ton, g) 2 [M] 2 kg 3 time (hours, years) 3 [T] 3 s

__**Derived** **Units**__ Volume [L]3 m3 Density (mass/volume) [M] / [L]3 kg / m3


 * Are the equations dimensionally correct?**

a) v = v + at v = __[L]__ a = __[L]__ t = [T] [T] [T]^2

__[L]__ ? __[L]__ + __[L]__ x [T] à __[L]__ = __[L]__ + __[L]__ YES! [T] = [T] [T]^2 [T] [T] + [T]

b) __[L]2__ = __[L]2__ + __2[L]__ [L] à  __[L]2__ = __[L]2__ + 2__[L]2__ YES!  [T]2 = [T]2 [T]2 [T]2 [T]2 [T]2


 * *show that every term on each side of the equal sign has the same dimensions. **
 * Aristotle’s Science (384 – 322 BC)**
 * study of nature was a search for “causes”

Stated that any object (animal, plant, inanimate, etc.) had 4 attributes; 1- **Matter** – where it came from (table) tree 2- **Form** – appearance (table) 4 legs, flat surface 3- **Moving** **cause** – maker / allowed to move (table) carpenter 4- **Final** **cause** – purpose (table) holding, support, eating off of

earth, air, water, fire
 * all substances are compounds of 4 elements

- an object not in its proper place would “strive” to get there.
 * he thought every object had its place determined by its “nature” and its make up

*could have circular motion, but that would only be “natural” for the “heavenly spheres” -circular motion had no beginning or end and repeated without deviation - made of 5th essence à quintessence
 * 2 types of motion**
 * ** __Natural Motion__ ** || ** __Violent Motion__ ** ||
 * Eg 1: a stone’s natural tendency if left alone and unsupported it to fall. || *results from pushing or pulling forces ||
 * Eg 2: up and down motion only || *imposed motion, imposed upon the natural motion ||
 * believed different rules applied to the heavens compared to the earth.

1- Heavier things fall faster, with speed being proportional to the weight 2- The speed of fall of a given object depends inversely on the density of the medium it is falling through. y = 1 / x 3- For violent motion: the speed of the moving object was directly proportional to the applied force a. Eg. If you stop pushing on an object it will naturally stop moving (natural state)
 * Aristotle’s Rules of Motion**

- 1st to try to use predictive equations to describe motion. Galileo followed him and was the first to start testing Aristotle’s predictions.
 * Kepler**

\_ _ _ _ _ _ _ Concept of Inertia - **inertia**: natural tendency for an object was to resist a change in its motion
 * Galileo (1564 – 1642)**
 * actually tested Aristotle’s statements
 * also noticed à \* */

maximum friction force between object and what they lie on - eg – pull table cloth out of underneath everything

Q) when there is a helium balloon in your car, and you slam on the breaks why does the balloon fly backwards as everything else shoots forward?

A) Air is heavier than helium and helium rises because it is less dense. When the car is breaking the air is going forward as well so the helium goes back to where there is now a low-density area.

** __Linear Motion Notes are at the bottom of the page__ Talks about Graphs and Kinematic eqauations in detail**


Force : a push/pull exerted on an object from the objects interaction with another object Vector Quantity : both the magnitude and the direction are important (a type of force)
 * Something capable of changing an objects state of motion, that is, changing its speed/velocity
 * SI unit: Newton (N)
 * When interaction ceases, the two objects no longer experience a force

1. Weight (“Fg” or “W”)
 * __Examples of Forces:__ **
 * The gravitational force (pull) on a body due to a nearby planet
 * Equation: Fg = W = Mag
 * ** __Weight__ ** || ** __Mass__ ** ||
 * Force (measure of the pull of gravity) || Measure of amount of substance ||
 * Vector quantity (direction matters) || Scalar quantity (direction doesn’t matter) ||
 * Varies depending on location || Doesn’t vary by location ||
 * Unit: N || Unit: Kg ||

2. Tension (“Ft” or “T”) 3. Normal Force (“Fn” or “N”) 4. Friction (“Ffr” or “f”)
 * When a cord (rope, cable, etc.) is attached to a body and is pulled taut, the cord pulls on the body with a force of tension, directed away from the body along the cord
 * When a body presses against a surface, the surface (even a seemingly rigid one) deforms and pushes back on the body with a normal force that is perpendicular to that surface.
 * A force directed along a surface, opposite the direction of intended motion, relative to that surface, due to bonding between the body and the surface.


 * __Free Body Diagrams (FBD)__ **
 * Shows the relative magnitude and direction of all forces acting upon an object in a given situation

= = **Click on the link at the bottom of the page to view different Free Body Diagrams Examples**

 Articles: 1. [] This article explains free fall motion and presents acceleration, position, and velocity over time graphs for free fall motion.

2. [] This article is an overview of what Aristotle believed to be true about physics (motion on objects, elements, etc.) and how Galileo overruled what Aristotle proposed.

3. [] This article is relevant because it talks about how whiplash happens. Whiplash is caused when the “weight of the body, through the law of physics called inertia, resists the impact and remains essentially motionless.” And when the body doesn’t move, but the head does because of the mobile neck, the neck snaps forward and causes whiplash. This is an example of Newton’s First Law and how an object will resist change in motion.

4. [] This article is relevant because it shows that because, despite the force of gravity, the force of air resistance will prevent an object to constantly accelerate at 9.8 m/s2 towards the ground. Air resistance will cause the penny to reach a terminal velocity in the air which will not be enough force to puncture a person no matter how high you drop it from. Unless dropped in a vacuum with no air resistance and where the could accelerate, this would not work.

Pictures: 1. [] This picture is of someone throwing a ball in the air and it shows the ball's entire flight path. This picture is an example of a free fall object (if you say that no other forces are acting upon the ball except the force of gravity). Thus, when the ball is thrown it begins with an initial velocity and an acceleration that is deccelerating in the positive direction at a constant rate at -9.8 m/s. At the ball's highest point, the velocity is momentarily zero. As the ball begins to fall back down, the acceleration accelerates in the negative direction at a constant rate of -9.8 m/s. Thus, the acceleration of the ball's flight path is always negative.

2. [] This picture portrays two racecars turning a corner. When moving in a constant direction the velocity can also be constant however it is impossible for it to stay the same while turning a corner unless it decelerates. One way, that we discusses in class, of not thaving to slow down as much was by the addition of a back "tail" and side wings. This forces the car to stay lower to the ground and thus creating more friction so when turning a corner the car does not lift as much.

3. [] This picture is of a soccer player kicking a soccer ball. Inertia is an objects natural tendency to resist a change in its motion. The ball at this picture is in a state of rest. A significant amount of force has to be applied to first, exceed the ball's inertia and then to send it in a certain direction for a certain amout of time and distance. The outside force working on the ball is the athlete's leg.

4. [] An object will want toremain at rest unless compelled to move by an outside force. A person sitting in a car that stops immediately would receive whiplash because the car is slowing down at a much faster rate than the person is. The seatbelt's lock helps the body of the person to slow down at a similar speed however their neck snaps forward. When it snaps back, the head rest helps to prevent whiplash because it stops the head from snapping backwards completely.

5. [] The force of gravity causes an apple to fall towards the ground. It goes from a state of rest in the tree to a state of rest on the ground. Both the initial and final velocities are 0 since it begins and ends at rest.

Video  [] This video shows the Newton’s First Law of inertia because an object will want to stay in its state of rest, unless compelled to change by an outside force. The plates, utensil, and cups will stay on the table even though the table cloth underneath it is moving because it will want to stay at rest. The table cloth underneath it is not moving fast enough to be a force to move those objects.

