lunes, 19 de septiembre de 2011

04 Waves & Wavelike motion

WAVES AND WAVELIKE MOTION


WHY WAVES ARE A SPECIAL KIND OF MOTION?

Vibrational Motion:

*Things wiggle.
*They do the back and forth.
*They vibrate;
*They shake;
*They oscillate.

These phrases describe the motion of a variety of objects. They even describe the motion of matter at the atomic level. Even atoms wiggle - they do the back and forth. Wiggles, vibrations, and oscillations are an inseparable part of nature.

What is the relationships between vibrational motion and waves?

Waves occur frequently in nature.

The most obvious examples are waves in water, on a dam, in the ocean, or in a bucket. We are most interested in the properties that waves have. All waves have the same properties so if we study waves in water then we can transfer our knowledge to predict how other examples of waves will behave.

What are waves?

*Waves are disturbances which propagate (move) through a medium.
*Waves can be viewed as a transfer energy rather than the movement of a particle.
*Particles form the medium through which waves propagate but they are not the wave. This will become clearer later.


01 WAVES MODEL

We can no see them, but we can describe them with a model


Crest:
*Region of maximum amplitude.
*The crest of a wave is the point on the medium that exhibits the maximum amount of positive or upward displacement from the rest position


Trough (Valle):
*Region of minimum amplitude.
*The trough of a wave is the point on the medium that exhibits the maximum amount of negative or downward displacement from the rest position.
*Points C and J on the diagram represent the troughs of this wave.

Node:
A standing wave is a pattern which results from the interference of two or more waves traveling in the same medium.  All standing waves are characterized by positions along the medium which are standing still.  Such positions are referred to as nodes. 

Amplitude (A):


*The characteristic height of a peak and depth of a trough is called the amplitude of the wave.
*The amplitude is defined as the maximum displacement of an object from its resting position.
*Normally the letter A is used for the amplitude of a wave. The units of amplitude are meters (m).

EXERCISE

The amount of energy carried by a wave is related to the amplitude of the wave. A high energy wave is characterized by a high amplitude; a low energy wave is characterized by a low amplitude.

A mass is tied to a spring and begins vibrating periodically.
The distance between its highest and its lowest position is 38 cm. What is the amplitude of the vibrations?

Answer: 19 cm
The distance that is described is the distance from the high position to the low position.
The amplitude is from the middle position to either the high or the low position.

Wavelength λ:

*The distance between two adjacent (next to each other) peaks is the same no matter which two adjacent peaks you choose. So there is a fixed distance between the peaks.
*Distance between one wave peak to the next.
*The units are meters (m).
*The wavelength of a wave is simply the length of one complete wave cycle.

Frequency (f):

*The frequency is the number of waves occurring within a unit of time (1 second).
*The frequency is defined as the number of complete cycles occurring per period of time
*Since the standard metric unit of time is the second, frequency has units of cycles/second, Hertz.

Period (T):
Now imagine you are sitting next to a pond and you watch the waves going past you. First one peak, then a trough, and then another peak. If you measure the time between two adjacent peaks you'll find that it is the same.
Waves have a characteristic time interval which we call the period of the wave and denote with the symbol T
The period is equal the time elapsing during the passage of one full wavelength and is measured in seconds.


This reciprocal relationship is easy to understand. After all, the two quantities are conceptual reciprocals (a phrase I made up). Consider their definitions as restated below:
period = the time for one full cycle to complete itself; i.e., seconds/cycle
frequency = the number of cycles that are completed per time; i.e., cycles/second


Example:


According to Wikipedia (and as of this writing), Tim Ahlstrom of Oconomowoc, WI holds the record for hand clapping.
He is reported to have clapped his hands 793 times in 60.0 seconds.
What is the frequency and what is the period of Mr. Ahlstrom's hand clapping during this 60.0-second period?

Answer:
In this problem, the event that is repeating itself is the clapping of hands; one hand clap is equivalent to a cycle.
Frequency = cycles per second
= 793 cycles/60.0 seconds = 13.2 cycles/s
= 13.2 Hz
Period = seconds per cycle
= 60.0 s/793 cycles = 0.0757 seconds

Exercise 01:
A pendulum is observed to complete 23 full cycles in 58 seconds.
Determine the period and the frequency of the pendulum.

Answer:
The frequency can be thought of as the number of cycles per second. Calculating frequency involves dividing the stated number of cycles by the corresponding amount of time required to complete these cycles. In contrast, the period is the time to complete a cycle. Period is calculated by dividing the given time by the number of cycles completed in this amount of time.
Frequency = 23 cycles/58 seconds
= 0.39655 Hz = ~0.40 Hz
Period = 58 seconds/23 cycles
= 2.5217 sec = ~2.5 s

Speed:

Now if you are watching a wave go by you will notice that they move at a constant velocity.
The speed is the distance you travel divided by the time you take to travel that distance.
This is excellent because we know that the waves travel a distance λ in a time T.

Speed = Wavelength / Period
Speed = Wavelength • Frequency v = (λ)(f)


A Wave Transports Energy and Not Matter


When a wave is present in a medium (that is, when there is a disturbance moving through a medium), the individual particles of the medium are only temporarily displaced from their rest position. There is always a force acting upon the particles that restores them to their original position. In a slinky wave, each coil of the slinky ultimately returns to its original position. In a water wave, each molecule of the water ultimately returns to its original position. And in a stadium wave, each fan in the bleacher ultimately returns to its original position. It is for this reason, that a wave is said to involve the movement of a disturbance without the movement of matter. The particles of the medium (water molecules, slinky coils, stadium fans) simply vibrate about a fixed position as the pattern of the disturbance moves from one location to another location.

Exercises


1. A medium is able to transport a wave from one location to another because the particles of the medium are ____.
a. frictionless
b. isolated from one another
c. able to interact
d. very light 

Answer: C
For a wave to be transmitted through a medium, the individual particles of the medium must be able to interact so that they can exert a push and/or pull on each other; this is the mechanism by which disturbances are transmitted through a medium.

2. In order for John to hear Jill, air molecules must move from the lips of Jill to the ears of John.
Answer ==> False.
A sound wave involves the movement of energy from one location to another, not the movement of material.
The air molecules are the particles of the medium, and they are only temporarily displaced, always returning to their original position.

LONGITUDINAL VS TRANSVERSE WAVES

Transverse waves

A transverse wave is a wave in which particles of the medium move in a direction perpendicular to the direction that the wave moves. Suppose that a slinky is stretched out in a horizontal direction across the classroom and that a pulse is introduced into the slinky on the left end by vibrating the first coil up and down. Energy will begin to be transported through the slinky from left to right.


As the energy is transported from left to right, the individual coils of the medium will be displaced upwards and downwards. In this case, the particles of the medium move perpendicular to the direction that the pulse moves. This type of wave is a transverse wave. Transverse waves are always characterized by particle motion being perpendicular to wave motion.


Exercises:

1. Mac and Tosh are experimenting with pulses on a rope.
They vibrate an end up and down to create the pulse and observe it moving from end to end.
How does the position of a point on the rope, before the pulse comes, compare to the position after the pulse has passed?

Answer:

The point returns to its original position.
Waves (and pulses) do not permanently displace particles from their rest position.

2. A transverse wave is transporting energy from east to west.
The particles of the medium will move_____.
a. east to west only
b. both eastward and westward
c. north to south only
d. both northward and southward

Answer: D
*The particles would be moving back and forth in a direction perpendicular to energy transport.
*The waves are moving westward, so the particles move northward and southward.

Longitudinal waves:

A longitudinal wave is a wave in which particles of the medium move in a direction parallel to the direction that the wave moves. Suppose that a slinky is stretched out in a horizontal direction across the classroom and that a pulse is introduced into the slinky on the left end by vibrating the first coil left and right. Energy will begin to be transported through the slinky from left to right.


As the energy is transported from left to right, the individual coils of the medium will be displaced leftwards and rightwards. In this case, the particles of the medium move parallel to the direction that the pulse moves. This type of wave is a longitudinal wave. Longitudinal waves are always characterized by particle motion being parallel to wave motion.



Exercises

1. Describe how the fans in a stadium must move in order to produce a longitudinal stadium wave.

Answer:
The fans will need to sway side to side.
Thus, as the wave travels around the stadium they would be moving parallel to its direction of motion.
If they rise up and sit down, then they would be creating a transverse wave.

Sound is a longitudinal wave

A sound wave traveling through air is a classic example of a longitudinal wave. As a sound wave moves from the lips of a speaker to the ear of a listener, particles of air vibrate back and forth in the same direction and the opposite direction of energy transport. Each individual particle pushes on its neighboring particle so as to push it forward. The collision of particle #1 with its neighbor serves to restore particle #1 to its original position and displace particle #2 in a forward direction.

This back and forth motion of particles in the direction of energy transport creates regions within the medium where the particles are pressed together and other regions where the particles are spread apart. Longitudinal waves can always be quickly identified by the presence of such regions. This process continues along the chain of particles until the sound wave reaches the ear of the listener.

Exercise:

Curly and Moe are conducting a wave experiment using a slinky. Curly introduces a disturbance into the slinky by giving it a quick back and forth jerk. Moe places his cheek (facial) at the opposite end of the slinky. Using the terminology of this unit, describe what Moe experiences as the pulse reaches the other end of the slinky.

Answer:
When the slinky reaches the end of the slinky and hits Moe in the cheek, Moe experiences a pulse of energy. The energy originated on Curly's end and is transported through the medium to Moe's end. The last particle on Moe's end transports that energy to Moe's cheek.

Exercise:

A wave is transporting energy from left to right. The particles of the medium are moving back and forth in a leftward and rightward direction.
This type of wave is known as a ____.
a. mechanical
b. electromagnetic
c. transverse
d. longitudinal

Answer: D
The particles are moving parallel to the direction that the wave is moving.
This must be a longitudinal wave.

II. Win one point for your October quiz





by solving next 3 sections:

domingo, 18 de septiembre de 2011

Proyecto (Feria de Ciencias)

OPCIONES DE PROYECTO DEL BIMESTRE 1 SEPTIEMBRE-OCTUBRE

Aprendizajes esperados:

• Trabaja colaborativamente con responsabilidad, solidaridad y respeto en la
organización y desarrollo del proyecto.
• Selecciona y sistematiza la información que es relevante para la investigación
planteada en su proyecto.
• Describe algunos fenómenos y procesos naturales relacionados con el movimiento, las ondas o la fuerza, a partir de gráficas, experimentos y modelos físicos.
• Comparte los resultados de su proyecto mediante diversos medios (textos,
modelos, gráficos, interactivos, entre otros).


DEBEN SEGUIR LOS PASOS DEL MÉTODO CIENTÍFICO PARA LA DOCUMENTACIÓN DE SU PROYECTO.

Opción 01:
Pregunta inicial ¿Cómo es el movimiento de los terremotos o tsunamis, y de qué manera se aprovecha esta información para prevenir y reducir riesgos ante estos desastres naturales?


*¿Por qué en la ciudad de México los sismos de gran magnitud causan tantos daños?
*¿Pueden prevenirse los desastres que provocan los sismos? ¿Cómo?
*Si en tu localidad se presenta un sismo de gran magnitud, ¿están preparados para enfrentarlo? ¿Qué acciones pueden seguir?
*¿Cuál es el papel de la sociedad civil antes, durante y después de un sismo?
*¿Pueden predecirse los sismos? ¿Cómo?
*¿Cómo puede construirse un sismógrafo sencillo?

Opción 02:
Pregunta inicial ¿Cómo se puede medir la rapidez de personas y objetos en algunos deportes; por ejemplo, béisbol, atletismo y natación?

*¿Cómo ha cambiado la velocidad de los atletas en distintas disciplinas a lo largo de los últimos 10 años?
*¿Qué procedimiento se puede seguir para medir con precisión la rapidez de un corredor en una pista?
*¿Por qué se busca tener mejores formas de medición del desempeño de los atletas?
*¿Qué equipos se utilizan actualmente en las carreras de velocidad de las olimpiadas? ¿Qué información puede medirse con ellos?
*¿Qué equipos se utilizan en el fútbol para describir el movimiento ejecutado por los futbolistas o por la pelota? ¿Qué tipo de información reportan?

Opción 03:
Pregunta inicial ¿Cómo potenciamos nuestros sentidos para conocer más y mejor?


*¿Cómo puedes construir un dispositivo que aumente tu percepción para ver mejor objetos pequeños?
*¿Qué aparato puedes elaborar para ver objetos muy lejanos?
*¿Con qué aparatos puedes amplificar el sonido de tu entorno?
*¿Cómo puedes construir un artefacto que sirva para observar vibraciones imperceptibles a simple vista?
*¿De qué manera puedes medir un movimiento muy lento, como el crecimiento de una flor?

Opción 04:
Pregunta inicial ¿Qué materiales se pueden magnetizar y qué aplicaciones tiene esta propiedad? (Trenes de levitación magnética)


*¿Qué son las auroras boreales, y cómo se producen?
*¿Por qué en nuestro país no son visibles las auroras boreales?
*¿Pueden los materiales perder su magnetismo? ¿Cómo y por qué?
*¿Cuáles son los materiales ferromagnéticos?
*¿Cuáles son algunas de sus aplicaciones tecnológicas?
*¿Qué tipo de aplicaciones tiene el magnetismo?
*¿Cuáles son los materiales paramagnéticos y diamagnéticos? ¿Qué aplicaciones tienen?
*¿Qué es el biomagnetismo? ¿Qué sucesos explica?
*¿Afecta a los seres humanos el magnetismo terrestre?

Opción 05:
Pregunta inicial ¿Qué materiales se pueden electrizar y qué aplicaciones tiene esta propiedad? (La fotocopiadora)


*¿Cómo se forman los relámpagos?
*¿Para qué sirven los pararrayos?
*¿Qué es una carga eléctrica? ¿Cómo se manifiesta la electrostática?
*¿Cómo se cargan eléctricamente los cuerpos?
*¿Qué relación hay entre electricidad y fuerza?
*¿Cómo se obtiene la fuerza eléctrica?
*¿Qué tipo de aplicaciones tiene el electromagnetismo?

ETAPAS DE UN PROYECTO


CRITERIOS DE EVALUACIÓN

HABILIDADES 50%
ACTITUDES Y VALORES 50%

jueves, 15 de septiembre de 2011

PREPARE FOR MONTHLY EXAM

Quiz 02 September Exam



REFERENCE POINT AND TRAJECTORY

1. What does relative motion mean? (Book Page 6)
2. What do you need to describe object’s motion?
3. What is a reference point? (Book Page 5
4. What is a reference system?
5. Give three examples of good reference points.
6. What is the difference between trajectory and displacement?
7. What does measurement mean?
8. What are the magnitudes related with motion? (Book Page 7)
9. What are the units in “International System of Units” for time and distance? (Book Page 7)
10. Why is convenient to the ISU to measure the distance? (Book Page 7)

1. ¿Qué significa que el movimiento es relativo?
2. ¿Qué necesitas para describir el movimiento de los cuerpos?
3. ¿Qué es un punto de referencia?
4. ¿Qué es un marco o sistema de referencia?
5. ¿Cuáles objetos son buenos punto de referencia?
6. ¿Cuál es la diferencia entre trayectoria y desplazamiento?
7. ¿Qué es medir?
8. ¿Qué magnitudes están relacionadas a la medición del movimiento?
9. ¿Cuáles son las unidades fundamentales en el SIU de la longitud y el tiempo?
10. ¿Por qué es conveniente usar el Sistema Internacional para medir la distancia?

DISTANCE, DISPLACEMENT, SPEED & VELOCITY

1. What is a magnitude or quantity?
2. What are scalars? Give 3 examples.
3. What are vectors? Give 3 examples.
4. What is the distance travelled?
5. What is displacement?
6. What’s the difference between distance travelled & displacement?
7. In what case do distance and displacement are the same?
8. What’s the formula to calculate an object’s speed? (Book Page 9)
9. What do you know about the motion of an object that is moving with a speed of 1 m/s? (Book Page 9)
10. What’s the difference between speed and velocity? (Book Page 12)

1. ¿Qué es magnitud?
2. ¿Qué es una magnitud escalar? Mencione tres ejemplos
3. ¿Qué es una magnitud vectorial? Mencione tres ejemplos
4. ¿Qué es la distancia recorrida?
5. ¿Qué es el desplazamiento?
6. ¿Cuál es la diferencia entre distancia recorrida y desplazamiento?
7. ¿Cuándo la distancia recorrida y el desplazamiento son iguales?
8. ¿Cómo se calcula la rapidez de un objeto móvil?
9. ¿Qué sabes acerca del movimiento de un objeto que tiene una rapidez promedio de 1 m/s?
10. ¿Cuál es la diferencia entre rapidez y velocidad?

lunes, 12 de septiembre de 2011

03 DISTANCE VS DISPLACEMENT; SPEED VS VELOCITY

Old word, new concepts

You have used words and phrases such as going fast, stopped, slowing down, speeding up, and turning provide a sufficient vocabulary for describing the motion of objects.
We will be expanding upon this vocabulary list with words such as distance, displacement, speed, velocity, and acceleration.

CLASS 01 SCALAR & VECTORS

Scalars are quantities that are fully described by a magnitude (or numerical value) alone.

Vectors are quantities that are fully described by both a magnitude and a direction.


Exercise 01 Consider the following quantities listed below. Categorize each quantity as being either a vector or a scalar.
a) 5 meters b) 30 m/sec, East c) 5 miles, North d) 20 degrees Celsius
e) 256 bytes f) 4000 Calories


CLASS 02 DISTANCE VS DISPLACEMENT

Distance and displacement are two quantities that may seem to mean the same thing yet have distinctly different definitions and meanings.


*Distance is a scalar quantity that refers to "how much ground an object has covered" during its motion.
*Distance can be defined as how far two objects are. Distance in physics may refer to physical length.
*Distance is the scalar path between two locations measured along path connecting them.

*Displacement is a vector quantity that refers to "how far out of place an object is"; it is the object's overall change in position.
*Displacement can be defined as shortest distance between the starting point and end point.
*Displacement can be defined as imaginary straight path which is different from the actual path.


In the figure you can see a rat and cheese.  If the rat want the cheese it must follow the blue path. And the length of blue path is the distance. Or it can be said in another way. How far the rat is from cheese. If you ask this question your self the result you get is nothing but the distance.

In the figure the green path present between the rat and cheese is the displacement because it is the shortest path.
So by this we can conclude displacement is a vector measure of the interval between two locations measured along the shortest path connecting them.





CLASS 03 SPEED VS VELOCITY

REACTIVATE
a) What do you think when you hear the word “Speed”?
b) Describe a sport or activity in which speed is important?
c) What examples are there of velocity?
d) Do these concepts mean the same?

SPEED

The motion of an airplane is fast. (260 m / second)
The motion of a snail is slow. (1 mm / second)
By using these words, your are describing the object’s speed.
The speed or the airplane is much greater that the speed of the snail because the airplane travels mucho farther than the snail in the same amount of time.


*Speed refers to "how fast an object is moving“
Speed is the rate of change in distance with respect to time.
*A fast-moving object has a high speed while a slow-moving object has a low speed. An object with no movement at all has a zero speed.
*The speed of an object is the distance the object moves per unit of time.

To calculate the speed of an object, divide the distance the object travels by the amount of time it takes to travel that distance. (m/s = meters per second):




Example 01: The motorcyclist has traveled a total distance of 24 Kilometers in 3 hours. What has his average Speed?

Exercise 01: While on vacation, Lisa Carr traveled a total distance of 440 miles. Her trip took 8 hours. What was her average speed?

Exercise 02: You are driving to Mexico to visit your Grandmas to eat her scrumpcious snickerdoodle cookies. In 5 hours you drove 1000 meters to stop for milk. You still had 940 more meters to go.
If you got to grandmas house in a total of 8 hours what is your average velocity between your milk rest and grandmas.



VELOCITY

Velocity refers to "the rate at which an object changes its position“.
Velocity is the rate of change in displacement with respect to time.


Example: You hear that a thunderstorm is travelling at a speed of 25 km/h. Should you prepare for the storm? Can you know the velocity of the storm?
What do you need?


Exercise 1: A car travels 90. meters due north in 15 sec.
Then the car turns around and travels 40. meters due south in 5.0 seconds.
What is the magnitude of the average velocity of the car during this 20 - second interval?
A)2.5 m/s B)5.0 m/s C)6.5 m/s D)7.5 m/s

Exerise 02: The position of an object is +35 meters at 2.0 seconds and is +87 meters at 15 seconds. Calculate the average velocity of the object.


REMEMBER:
If you know the distance an object travels in a certain amount of time, you can calculate the speed of the object.
When you know both the speed and the direction of an object´s motion, you know the velocity of the object.


MOTION CONCEPTS (IN SPANISH)

MAGNITUD VECTORIAL: Requiere de unidad y dirección para ser especificada:
25 Km/h N, 30 N al este, 30 Km Sur.

MAGNITUD ESCALAR: Requiere sólo de unidad para ser especificada:
½ Kg de tortillas, 36 minutos, 4 metros, 20°F

DISTANCIA RECORRIDA: Es la longitud de la trayectoria. La distancia recorrida por un objeto no considera la dirección en que lo hizo, sólo indica la longitud del recorrido.

DESPLAZAMIENTO: Longitud en línea recta desde la posición inicial hasta la posición final. El desplazamiento es diferente porque corresponde a una distancia medida en una dirección particular entre el punto de partida y el de llegada.

METRO / SEGUNDO:Unidad fundamental para representar la rapidez en el SIU.

DIRECCIÓN: Rumbo. Línea de movimiento de un cuerpo.

RAPIDEZ: Distancia recorrida por un cuerpo en un cierto tiempo, sin considerar su dirección:

VELOCIDAD: Cambio de posición de un cuerpo en un cierto tiempo (Rapidez + dirección). La velocidad es un vector y por ello puede representarse mediante flechas

La rapidez indica qué tan rápido se mueve un objeto, mientras que la velocidad, no sólo menciona qué tan rápido se mueve el objeto, sino que además indica la dirección en la que éste se mueve.

Dos objetos que viajan a la misma rapidez tienen diferentes velocidades si ellos
Comienzan en diferentes tiempos
Viajan distancias diferentes
Se mueven en diferentes direcciones


II. Win 1 point in your quiz by applying the concepts of distance, displacement, speed, and direction that you learned in this week. Due date: Monday September/19/2011.

miércoles, 7 de septiembre de 2011

FIRST QUIZ SEPTEMBER 9/2011

Hi, students. On FRIDAY september 9 is my birthday and also is the FIRST QUIZ. Please ANSWER the following 20 QUESTIONS IN ENGLISH in order to get the PASS for the exam.

Study guide for Quiz 00: What does Physics study?

1. What is Physics?
2. What is Chemistry? What’s the difference with Physics?
3. What are the natural phenomena that Physics study?
4. What is a chemical change? Give three examples.
5. What is a physical change? Give three examples
6. What is the scientific method?
7. What are the steps of scientific method given in order?
8. What is a scientific model? Say one example.
9. What is a scientific law? Say one example.
10. What is a scientific theory? Say one example.

Guía de estudio para el Quiz 00: Qué estudia la Física?

1. ¿Qué es la Física?
2. ¿Qué es la Química? ¿Cuál es la diferencia con la Física?
3. ¿Cuáles son los fenómenos que estudia la Física?
4. ¿Qué es un cambio químico?
5. ¿Qué es un cambio físico?
6. ¿Qué es el método científico?
7. ¿Cuáles son los pasos ordenados del método científico?
8. ¿Qué es un modelo científico? Menciona un ejemplo.
9. ¿Qué es una ley científica? Menciona un ejemplo.
10. ¿Qué es una teoría científica? Menciona un ejemplo

Study guide for Quiz 01: Motion. Are you moving?

1. How do we know something is in motion?
2. What is motion (movement)?
3. What is a mobile?
4. What are the advantages and limitations of our five senses to perceive that something is in motion?
5. How do you distinguish if an object is moving fast or slow by using your senses?
6. What devices and techniques has human being invented to help our senses?
7. How can we analyze the slow motion of galaxies and stars?
8. How can we analyze the fast motion of a humming bird?
9. How can we know if an airplane brings closer or moves away?
10. What are stroboscope, stethoscope and telescope used for?

Guía de estudio para el Quiz 01: Movimiento. Te estás moviendo?

1. ¿Cómo sabemos que algo se mueve?
2. ¿Qué es el movimiento?
3. ¿Qué es un móvil?
4. ¿Cuáles son las ventajas y limitaciones de los cinco sentidos para percibir o saber que algo se mueve?
5. ¿Cómo distingues si un objeto se mueve rápido o lento a partir de lo que percibes?
6. ¿Qué aparatos y técnicas ha inventado el ser humano para contrarrestar la limitante de sus sentidos?
7. ¿Cómo se puede analizar el movimiento lento de las galaxias y el de las estrellas?
8. ¿Cómo se puede analizar el movimiento rápido de los colibríes?
9. ¿Cómo sabemos que un avión se acerca o se aleja, aún sin mirarlo?
10. ¿Para qué sirven un estroboscopio, un estetoscopio y un telescopio?

lunes, 5 de septiembre de 2011

02 REFERENCE POINT AND TRAJECTORY

HOW DO WE DESCRIBE OBJECT'S MOTION?

When is an object in motion?

*Deciding if an object is in motion is not as easy as you might think. For example, you are probably sitting in a chair as you read this ppt presentation. Are you moving?
*Parts of you are. Your eyes blink and your chest moves up and down. But you would probably say that you are not moving.
*An object is in motion if its position changes relative to another object.
*Because your position relative to your chair does not change, you could say that you are not in motion.


Physical problems



You are inside a bus in a bus terminal. There are several buses aligned with yours and the bus close to you moves backward very slowly.
Your seat partner says: “We have started to move”. However, for you, the bus is still at repose. Who is right? Explain your answer.

REFERENCE POINT

*To decide if you are moving, you use your chair as a reference point.
*A reference point is a place or object used for comparison to determine if something is in motion.
*An object is in motion if it changes position relative to a reference point.
*Objects that are fixed relative to Earth (such as a building, a tree, or a sign, the classroom corner, the center of a field) make good reference points.

Juan está jugando con su vecino a las canicas. La mamá de Juan observa al niño desde la puerta de su casa. En eso llega su papá manejando el vehículo, listo para estacionarlo en su casa y también observa al niño. ¿Quién cuenta con el mejor punto de referencia, el papá o la mamá?

What objects could serve as good reference points?


RELATIVE MOTION

*If you use a chair as your reference point as you sit and pay attention to the professor, you are not moving.
*If you choose another object as a reference point, you may be moving.
Earth moves around the sun at a speed of about 30 km/second. But because you are moving with Earth, you don not seem to be moving.

TRAJECTORY




*A trajectory is the path that a moving object follows through space as a function of time.


Another word similar to trajectory:
Way road path journey track course trail pathway avenue
Lane distance line itinerary

Describe the trajectory of each motion.
Rectilinear Circular Elliptical Parabolic Vibratory
Rotational Oscilatory Zig zag Random


¿Cómo es la trayectoria de?
Una gota de lluvia cayendo
Un joven manejando una bici
Una mariposa volando en el campo
La Tierra moviéndose alrededor del sol
La Tierra moviéndose alrededor de su eje
Los juegos mecánicos en una feria
Rueda de la fortuna

CONCEPTOS IMPORTANTES EN ESPAÑOL:

MOVIMIENTO: Es el cambio de posición de un cuerpo en el tiempo, tomando como referencia a otros cuerpos y siguiendo una trayectoria.

PUNTO DE REFERENCIA: Punto fijo de origen sobre el cual se basan los cambios de posición. Sirve para saber si algo se movió o no, para establecer respecto a qué se movió. Un buen ejemplo es un edificio o un árbol. Malos ejemplos son una mariposa y un automóvil.

TRAYECTORIA: Los cuerpos al moverse, lo hacen de muchas maneras. La trayectoria es la línea que describe la ruta seguida por un objeto en movimiento. En las ferias, el movimiento que efectúa la rueda de la fortuna es circular.
Las unidades de LONGITUD y TIEMPO utilizadas para medir los movimientos de los corredores en una competencia de atletismo son el METRO y el SEGUNDO.

Para DESCRIBIR CON PRESICIÓN algún fenómeno de la naturaleza, primero necesitamos observarlo y determinar sus magnitudes; es decir: medirlo.
LONGITUD: Distancia entre dos puntos
TIEMPO: Lapso que caracteriza la duración de un fenómeno.
METRO: Unidad fundamental para representar la distancia de acuerdo al Sistema Internacional
SEGUNDO: Unidad fundamental para medir el tiempo en el Sistema Internacional de Unidades.

II. Prepare yourself for the weekly quiz of trajectory and reference point.

III. Win 1 or 2 point for your quiz by preparing an exposition to explain what follows:

01 MOTION: ARE YOU MOVING?

REACTIVATE

1. What do you understand with the word “motion”?
2. What are some motions of your environment?
3. How do we know when a body is in repose or in motion?
4. Do you know something that doesn’t move?
5. How do we describe the motion of objects?
6. What would happen if there wasn’t motion?





Physical problems

What motion do you make in the morning?
What is your favorite movement in soccer?
What is your favorite motion in jazz or dance?

WHAT IS MOTION?

Motion: Change in an object’s position from an original position to a final position over the time.

Motion is anything that occurs in two physical positions.
Motion takes place in two of the physic’s consecutive instants in time.
Motion is whatever unifies space and time because it can never take place without the two.

10 interesting facts about motion:

If there is no motion. There is no life.
What things can happen in 0.4 seconds?
*A mosqutio move its wings 200 times.
*The high frecuency radio waves (VHF) oscillates 40 million times.
*A train can advance 13 meters.
*A comercial airplane travels near 90 meters.
*Sound travels 136 meters.
*Earth travels 12 kilometer in its orbit around the sun.
*Light travels 120 000 km


The importance and limits of our senses


REACTIVATE
How do you recognize if something is moving or not?
What senses do we use to percieve the bus motion? Describe the experience using each sense.
Do all people percieve motion in the same way than you. Why?


There are many things in nature that we don´t percieve until they move.

*Some chameleon species are able to change their skin colors.
Different chameleon species are able to change different colors which can include pink, blue, red, orange, green, black, brown, light blue, yellow, turquoise and purple

*Hummingbirds are birds that comprise the family Trochilidae. They are among the smallest of birds, most species measuring in the 7.5–13 cm (3–5 in) range. Indeed, the smallest extant bird species is a hummingbird, the 5-cm Bee Hummingbird.
They can hover in mid-air by rapidly flapping their wings 12–90 times per second (depending on the species). They are also the only group of birds able to fly backwards.
Their English name derives from the characteristic hum made by their rapid wing beats. They can fly at speeds exceeding 15 m/s (54 km/h, 34 mi/h).

II. Prepare for your weely quiz.


III. Win 1 or 2 points explaining what follows.



CONCEPTOS IMPORTANTES EN ESPAÑOL:

*La cinemática, que estudia el movimiento de los cuerpos, es una de las ramas más fascinantes de la Física.

*La vista nos permite percibir el movimiento de un avión que se encuentra a una distancia lejana con respecto al lugar en que nos encontramos porque cambia de lugar.

*En un día lluvioso, a través de nuestros sentidos, podemos percibir el movimiento de las hojas de los árboles, las nubes, los pájaros, el correr del agua sobre el suelo, la luz y el sonido del viento; es decir, cuando cambian los cuerpos de lugar en un determinado lapso de tiempo.

MECÁNICA: Rama de la Física que estudia lo referente al movimiento de los cuerpos.

MOVIMIENTO: Es el cambio de posición de un cuerpo en el tiempo.

*A pesar de que no podemos ver el aire, apreciamos sus efectos cuando se mueve en forma de viento