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Hbsc2203 810809025494 teaching science for lower primary iii

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Hbsc2203 810809025494 teaching science for lower primary iii

  2. 2. HBSC2203 TEACHING SCIENCE FOR LOWER PRIMARY III ROSYIDAH BT IBRAHIM 810809025494 2 CONTENTS NO. CONTENTS PAGES 1 Introduction 3 2 Question(a)  Terminal Velocity 4 – 7 3 Question(b)  Theory of Light (Sunset Phenomena) 8 – 10 4 References 11
  3. 3. HBSC2203 TEACHING SCIENCE FOR LOWER PRIMARY III ROSYIDAH BT IBRAHIM 810809025494 3 Introduction This time, we will discuss about terminal velocity and light. Both of these things are very important topics in physic. Speed and velocity are often thought to mean the same thing. However, there is an important difference between speed and velocity. Velocity involves direction as well as magnitude, and is therefore a vector quantity. Speed on the other hand involves magnitude only, and is therefore a scalar quantity. The velocity of an object is defined as the distance travelled in a given time interval, in a specified direction. Velocity also can be defined as the rate of change of displacement with time. As a vector quantity, the velocity should be stated with both magnitude and the direction. However in simple calculations that deal with objects moving in a straight line, in a constant direction, the direction of the velocity is at times ignored. Velocity is also measured in metres per second (𝑚 𝑠−1 ), centimetres per second (𝑐𝑚 𝑠−1 ) and kilometres per hour(𝑘𝑚 ℎ−1 ). Now let’s get to know about light in general. The light is a form of energy. It can stimulate the light-sensitive cells in the retina of the eyes to create an impulse for the brain to see the form and colour of an object. Luminous objects can emit light into our eyes for them to be seen directly. Such objects include the Sun, stars, fireflies, photo-plankton, flames and lamps. Most objects, such as books, pictures and landscapes are non-luminous and cannot emit their own light for them to be seen directly. They can be seen only when they reflect light from the Sun or other light sources like lamps. The light travels in straight lines. Velocity = 𝑑𝑖𝑠𝑝𝑙𝑎𝑐𝑒𝑚𝑒𝑛𝑡 𝑡𝑖𝑚𝑒
  4. 4. HBSC2203 TEACHING SCIENCE FOR LOWER PRIMARY III ROSYIDAH BT IBRAHIM 810809025494 4 Question (a) The terminal velocity of a falling body occurs during free fall when a falling body experiences zero acceleration. This is because of the retarding force known as air resistance. Air resistance exists because air molecules collide into a falling body creating an upward force opposite gravity. This upward force will eventually balance the falling body's weight. It will continue to fall at constant velocity known as the terminal velocity. Source: Tom Henderson. Skydiving. Glenbrook South High School. Reproduced with the permission of the author. The magnitude of terminal velocity depends on the weight of the falling body. For a heavy object, the terminal velocity is generally greater than a light object. This is because air resistance is proportional to the falling body's velocity squared. For an object to experience terminal velocity, air resistance must balance weight. An example that shows this phenomenon was the classic illustration of a rock and a feather being dropped simultaneously. In a vacuum with zero air resistance, these two objects will experience the same acceleration. But on the earth this is not true. Air resistance will equal weight more quickly for the feather than it would for the rock. Thus the rock would accelerate longer and experience a terminal velocity greater than the feather. Another factor that affects terminal velocity is the orientation at which a body falls. If an object falls with a larger surface area perpendicular to the direction of motion it will experience a greater force and a smaller terminal velocity. On the other hand, if the object fell with a smaller surface area perpendicular to the direction of motion, it will experience a smaller force and a greater terminal velocity. The terminal velocity for a skydiver was found to be in a range from 53 m/s to 76 m/s. Four out of five sources stated a value between 53 m/s and 56 m/s. Principles of Physics stated a value of 76 m/s. This value differed significantly from the others. Then again, the value is variable since the weight and the orientation of the falling body play significant roles in determining terminal velocity.
  5. 5. HBSC2203 TEACHING SCIENCE FOR LOWER PRIMARY III ROSYIDAH BT IBRAHIM 810809025494 5 Terminal velocity is often reported to be approximately 60 m/s for a typical skydiver in free fall. Exceptional skydivers are able to increase this value considerably by diving head first with their arms against the sides of their bodies, legs held firmly together, and toes pointed. This posture presents a minimal projected area perpendicular to the direction of motion thus reducing aerodynamic drag. Special helmets and slick body suits reduce drag even further. On 16 August 1960, US Air Force Captain Joseph Kittinger entered the record books when he stepped from the gondola of a helium balloon floating at an altitude of 31,330 m (102,800 feet) and took the longest skydive in history. As of the writing of this supplement 39 years later, his record remains unbroken. The air is so thin at this altitude that it would make for a moderate laboratory vacuum on the surface of the earth. With little atmosphere, the sky is essentially black and the sun's radiation is unusually intense despite polar temperatures. Sitting in my gondola, which gently twisted with the balloon's slow turnings, I had begun to sweat lightly, though the temperature read 36 degrees below zero Fahrenheit. Sunlight burned in on me under the edge of an aluminized antiglare curtain and through the gondola's open door. The density of air at 30 km is roughly 1.5 % that at sea level and thus drag is essentially negligible. No wind whistles or billows my clothing. I have absolutely no sensation of the increasing speed with which I fall. [The clouds] rushed up so chillingly that I had to remind myself they were vapor and not solid.
  6. 6. HBSC2203 TEACHING SCIENCE FOR LOWER PRIMARY III ROSYIDAH BT IBRAHIM 810809025494 6 This is not true for skydivers at ordinary altitudes, which is why they reach terminal velocity and cease to accelerate. According to Captain Kittinger's 1960 report in National Geographic, he was in free fall from 102,800 to 96,000 feet and then experienced no noticeable change in acceleration for an additional 6,000 feet despite having deployed his stabilization chute. This gave him an unprecedented 3900 m (12,800 feet) over which to accelerate. At such extreme altitudes the acceleration due to gravity is not the standard 9.81 m/s2, but the slightly lower value of 9.72 m/s2. Using these numbers, it is possible to calculate the maximum theoretical velocity experienced during this record-setting jump. The result is amazingly close to the value recorded in National Geographic. As one would expect the actual value is slightly less than the theoretical value. This agrees with the notion of a small, but still non-zero, amount of drag. At nine-tenths the speed of sound, Captain Kittinger also holds the record for the greatest speed attained by a human without the use of an engine. The standard value of the speed of sound in air at 31,000 m is 300 m/s (670 mph). Given this, why then do so many sources report that Kittinger exceeded the speed of sound? One possible answer comes from the relatively obvious similarity between Kittinger's self-reported value of 614 mph and the most frequently misreported value of 714 mph (319 m/s). Somebody must have heard 614 but entered 714 accidentally into some officious document (like an encyclopedia). Some other people read the error and then reported it as fact. Many more people read these "facts" and suddenly nearly everyone was remembering the day Captain Kittinger broke the sound barrier. Another factoid is born. In the same way that science fiction humanoids appear human but are alien, real life factoids appear factual but are false. A factoid is a statement reported as truth that has, in fact, never been verified. Factoids are the scientific research of "they".  "They say that cell phones cause brain cancer."  "They say that margarine is better for you than butter."  "They say that toilets spin the other way around in Australia."  "They say that cows produce more milk when they listen to classical music than when they listen to rock and roll."
  7. 7. HBSC2203 TEACHING SCIENCE FOR LOWER PRIMARY III ROSYIDAH BT IBRAHIM 810809025494 7 At least, that's the way I see it. In a fantastic irony, people have started using the word factoid to mean a fact that can be stated briefly. I would call that a "factette". In the same way that a cigarette is a small cigar, a factette is a small fact. The definition of factoid is itself becoming a factoid. Captain Kittinger most likely did not exceed the speed of sound on 16 August 1960. To do so would have required an additional 1,300 m (4,200 feet) of free fall. That's a pretty large distance. I think he would have noticed it. This in no way detracts from his truly amazing accomplishment. Two skydivers intend to break Joseph Kittinger's 1960 world record parachute jump: Cheryl Stearns of the United States and Rodd Millner of Australia. Stearns is scheduled to jump over New Mexico in October 2001. Millner is planning his jump over Alice Springs in March 2002. Both skydivers plan to jump from an altitude of 40 km (130,000 feet) -- 8 km (5 miles) higher than Captain Kittinger. With this additional distance, it is quite possible that one of these jumpers will exceed the speed of sound. If we assume an average acceleration of 9.70 m/s2, it is a simple matter to determine the altitude at which a skydiver starting at 40 km would break the sound barrier. That's an altitude of about 116,000 feet. Keeping in mind that Captain Kittinger claimed not to sense any appreciable loss of acceleration until reaching 90,000 feet (27,430 m) it is now possible to project the next world record skydiving speed. It is doubtful that Stearns or Millner would actually reach anything near this speed, which is nearly 200 m/s faster than the local speed of sound. At the incredible speeds we're dealing with, air resistance cannot be ignored. Stearns' prediction of Mach 1.3 seems very reasonable compared to my prediction of Mach 1.6.
  8. 8. HBSC2203 TEACHING SCIENCE FOR LOWER PRIMARY III ROSYIDAH BT IBRAHIM 810809025494 8 Question (b) Light is part of the electromagnetic spectrum, the spectrum is the collection of all waves, which include visible light, Microwaves, radio waves (AM, FM, SW ), X-Rays, and Gamma Rays. In the late 1600s, important questions were raised, asking if light is made up of particles, or is it waves. Sir Isaac Newton, held the theory that light was made up of tiny particles. In 1678, Dutch physicist, Christiaan Huygens, believed that light was made up of waves vibrating up and down perpendicular to the direction of the light travels, and therefore formulated a way of visualising wave propagation. This became known as 'Huygens' Principle'. Huygens theory was the successful theory of light wave motion in three dimensions. Huygen, suggested that light wave peaks form surfaces like the layers of an onion. In a vacuum, or other uniform mediums, the light waves are spherical, and these wave surfaces advance or spread out as they travel at the speed of light. This theory explains why light shining through a pin-hole or slit will spread out rather than going in a straight line (see diffraction). Newton's theory came first, but the theory of Huygens, better described early experiments. Huygens' principle lets you predict where a given wave front will be in the future, if you have the knowledge of where the given wave front is in the present. At the time, some of the experiments conducted on light theory, both the wave theory and particle theory, had some unexplained phenomenon, Newton could not explain the phenomenon of light interference, this forced Newton's particle theory in favour of the wave theory. This difficulty was due to the unexplained phenomenon of light Polarisation - scientists were familiar with the fact that wave motion was parallel to the direction of wave travel, NOT perpendicular to the to the direction of wave travel, as light does. In 1803, Thomas Young studied the interference of light waves by shining light through a screen with two slits equally separated, the light emerging from the two slits, spread out according to Huygen's principle. Eventually the two wave fronts will overlap with each other, if a screen was placed at the point of the overlapping waves, you would see the production of light and dark areas (see interference). Later in 1815, Augustin Fresnel supported Young's experiments with mathematical calculations. In 1900 Max Planck proposed the existence of a light quantum, a finite packet of energy which depends on the frequency and velocity of the radiation. In 1905 Albert Einstein had proposed a solution to the problem of observations made on the behaviour of light having characteristics of both wave and particle theory. From work of Plank on emission of light from hot bodies, Einstein suggested that light is composed of tiny particles called photons, and each photon has energy.
  9. 9. HBSC2203 TEACHING SCIENCE FOR LOWER PRIMARY III ROSYIDAH BT IBRAHIM 810809025494 9 Light theory branches in to the physics of quantum mechanics, which was conceptualised in the twentieth century. Quantum mechanics deals with behaviour of nature on the atomic scale or smaller. As a result of quantum mechanics, this gave the proof of the dual nature of light and therefore not a contradiction. To understand why the sky goes red just before the sun goes down we also need to understand why the sky is blue for the rest of the time between sunrise and sunset. We are familiar with the sky usually being blue so we tend to think that red sunsets must be caused by 'something else', and accept that the sky 'just is' blue. Red and blue are words we use to describe different colours (or wavelengths) of light, so that gives us a clue; at different times of the day we are seeing different wavelengths of sun light. When the sun is low down on the horizon (rising and setting) the sky is red, and when the sun is higher in the sky we see blue light. So, what changes between the sun being low down and high up in the sky? We know that the sun radiates the same wavelengths of light all the time, so we know it can't be the sun only producing red light at dawn and dusk and blue light all the rest of the day. In fact, the thing that causes us to see different colours is the atmosphere. Apart from being made of different gasses, the atmosphere also contains billions of dust particles and water droplets. Sunlight is scattered as it encounters these particles and molecules, with short wavelengths being more efficiently scattered than long wavelengths. This is called Rayleigh Scattering.
  10. 10. HBSC2203 TEACHING SCIENCE FOR LOWER PRIMARY III ROSYIDAH BT IBRAHIM 810809025494 10 Blue light has a shorter wavelength than red light and, at sunset when the sun is low on the horizon, the sunlight has to pass through more atmosphere than it does when the sun is directly overhead. This means that as the sun sets the blue light has been filtered out by the thicker layer of atmosphere, leaving only the red, orange and yellow light for us to see. And, of course, for the rest of the day when the sun is overhead it has to pass through less atmosphere before we see it, so the blue light hasn't been scattered - and we can still see it! When the sun is overhead the light passes through the least thickness of atmosphere before we see it. The blue light hasn't been scattered so we can still see it. When the sun is low on the horizon the light has to travel through a thicker layer of atmosphere so the blue light is scattered and lost. We see only the longer wavelengths such as red, orange and yellow. 2553 words
  11. 11. HBSC2203 TEACHING SCIENCE FOR LOWER PRIMARY III ROSYIDAH BT IBRAHIM 810809025494 11 References Alert, G. (-, - -). The Physics Factbook. Retrieved February 15, 2011, from Speed of a Skydiver (Terminal Velocity): http://hypertextbook.com/facts/JianHuang.shtml Hassan, D., & Samsudin, M. A. (2010). HBHE2203:Teaching Science For Lower Primary III. Seri Kembangan: Meteor Doc Sdn. Bhd. Kiat, Y. E., & Kow, K. G. (2011). Essential Physics Form 4. Petaling Jaya: Pearson Malaysia Sdn. Bhd. Oenoki, K. (2009, - -). Velocity. Retrieved March 13, 2011, from Think Quest: http://library.thinkquest.org/10796/ch2/ch2.htm Siegal, E. (2009, September 8). Science Blogs. Retrieved March 13, 2011, from Starts With Bang: http://scienceblogs.com/startswithabang/2009/09/red_sky_at_night_but_why.php Yong, T. C., Weiyang, L., & Weishu, L. (2000, - -). iLight. Retrieved March 13, 2011, from Think Quest: http://library.thinkquest.org/C001377/laws.htm