Didatik Analysis of Inertia Concept

By:

Abraham Z. Ilyaz

Vinson Baidis

John Magian

webmaster

 

Introduction

Now a day the challenge in education field is very big especially for those who involve directly in this field. Not only Malaysia but also faced by many countries all around the world. They are many strategies has been created to makes the learning process becomes more effective. But effective learning process cannot be achived if the teacher has not prepared his or her self with knowledge about what he or she going to teach. One way to solve this problem is with preparing more knowledge about the concept that used in any skills that we are going to teach. This assignment is a part of physics teaching method (TT4133) course. The aim of this assignment is to provide physics teacher or future physics teacher to understand and know very well about inertia concept.

There are three main subtopics that will be discussed in this assignment. The first one is Conceptual Analysis of Curriculum Specification About Inertia.  Here we are going to discuss about inertia concept in general. The second is Analysis Of Text Book Presentation. In this subtopic, we are trying to analyze a textbook that used in form 4 physics classroom. We will also analyze a few other books about what they have mentions about inertia concept, learning and teaching strategies and the activities suggested, and also the example given.

          Finally, Student Alternative Conceptions About Inertia Concept. Here we are trying to analyze the student conceptions about inertia according to the journals and also from online sources.

 

1.                 Conceptual Analysis of Curriculum Specification About Inertia

This analysis is based to the Physics Form 4 Curriculum Specification. In this part we are going to discuss about inertia concept in general.

Aristotle believed that objects of matter were normally at rest. In order to move an object of matter with constant motion, Aristotle thought that a constant force had to be applied to the object. When the force was removed the object would return to a normal at rest condition.

The property of inertia for objects of matter was experimentally discovered by Galileo.  Galileo was then able to define that an object of matter at rest would remain at rest unless acted upon by an external force and an object in constant motion would remain in constant motion unless acted upon by an external force. The "inertia" of the matter enables it to maintain a static and dynamic existence.

Newton then developed laws of motion that elaborated on concepts developed by Galileo.  Newton defined a property of inertia as an "innate force of matter" and established the quantitative concept of "mass".  A measurement of the quantity of inertia with units of "mass" enabled the development of Classical Mechanics.

Einstein later showed that the quantity of "mass", or "innate force of matter", is related to a quantity of energy that an object of matter possesses.  This established the value of "mass" of an object as a variable quantity.  It was necessary for Einstein to describe "mass" in this fashion to maintain a principal of constancy for the velocity of light.

From previous assumptions in physical theory, "matter" and its inertial measurement "mass", are considered to be equivalent.  Any object containing a specific quantity of "matter" has a proportionately equal inertial measurement of "mass".  This may be an inaccurate description of the relationship between "matter" and "mass", as indicated by Einstein's relativity theories. If a single proton is accelerated to a velocity where it's mass value is doubled, is the quantity of matter also doubled? Logically, since the object of matter is still a single proton, rather than two protons, it should not be assumed that the quantity of matter has also doubled. For now, the concept of "mass" should be accepted at "face value" for the purpose it was intended, to provide a means to measure inertia, the ability to maintain static and dynamic existence.   

When Michael Faraday wrote, 'matter is everywhere present and there is no intervening space unoccupied by it', perhaps he would have been more accurate if he used the word "mass" rather than "matter".  The term "matter", for physical modeling purposes, should be reserved for structural objects that have an inertial measurement of "mass".  Although Faraday is probably accurate in his assumption that "space" can be quantitatively measured with units of "mass" his choice of words could have been better.  After all, Faraday maintained that "space" is an extension of objects of "matter", to make a statement that "matter" and the "space" which results from the existence of "matter" are equivalent is somewhat nonsensical.  Anyway, this seems to be a language problem.  Faraday pointed out some key issues in physical theory that needed, and still need attention.

James Clerk Maxwell elaborated on Faraday's concepts concerning "matter", the resulting "space", and the force fields that define "space".  Later Einstein maintained that Maxwell's work is accurate in any "inertial reference frame" without accepting the methods, or foundations, that Maxwell used to develop conclusions.  As a result, although Einstein indicated "distortions" that exist in "space", Einstein's conclusions are probably not completely accurate. Therefore, work still needs to be done.  The purpose of the following information is to indicate the need for improved definition of physical theory.  Although Faraday, as indicated previously, may not of communicated his ideas with proper language, Newton was very particular about the language he used to express his concepts concerning physical reality, Classical Mechanics.

 

Galileo and the Concept of Inertia

Galileo, the premier scientist of the seventeenth century, developed the concept of inertia. Galileo reasoned that moving objects eventually stop because of a force called friction. In experiments using a pair of inclined planes facing each other, Galileo observed that a ball would roll down one plane and up the opposite plane to approximately the same height. If smoother planes were used, the ball would roll up the opposite plane even closer to the original height. Galileo reasoned that any difference between initial and final heights was due to the presence of friction. Galileo postulated that if friction could be entirely eliminated, then the ball would reach exactly the same height.

Galileo further observed that regardless of the angle at which the planes were oriented, the final height was almost always equal to the initial height. If the slope of the opposite incline were reduced, then the ball would roll a further distance in order to reach that original height.

Figure 1

 

Galileo's reasoning continued - if the opposite incline were elevated at nearly a 0-degree angle, then the ball would roll almost forever in an effort to reach the original height. And if the opposing incline was not even inclined at all (that is, if it were oriented along the horizontal), then ... an object in motion would continue in motion....

 

Figure 2

 

Inertia and Mass

Newton's first law of motion states that "An object at rest tends to stay at rest and an object in motion tends to stay in motion with the same speed and in the same direction unless acted upon by an unbalanced force." Objects "tend to keep on doing what they're doing." In fact, it is the natural tendency of objects to resist changes in their state of motion. This tendency to resist changes in their state of motion is described as inertia.

 

Inertia = the resistance an object has to a change in its state of motion.

 

Newton's conception of inertia stood in direct opposition to more popular conceptions about motion. The dominant thought prior to Newton's day was that it was the natural tendency of objects to come to a rest position. Moving objects, so it was believed, would eventually stop moving; a force was necessary to keep an object moving. But if left to itself, a moving object would eventually come to rest and an object at rest would stay at rest; thus, the idea which dominated people's thinking for nearly 2000 years prior to Newton was that it was the natural tendency of all objects to assume a rest position.

 

Forces Do not Keep Objects Moving

Isaac Newton built on Galileo's thoughts about motion. Newton's first law of motion declares that a force is not needed to keep an object in motion. Slide a book across a table and watch it slide to a rest position. The book in motion on the table top does not come to a rest position because of the absence of a force; rather it is the presence of a force - that force being the force of friction - which brings the book to a rest position. In the absence of a force of friction, the book would continue in motion with the same speed and direction - forever! (Or at least to the end of the table top.) A force is not required to keep a moving book in motion; in actuality, it is a force, which brings the book to rest.

Figure 3

 

Mass as a Measure of the Amount of Inertia

All objects resist changes in their state of motion. All objects have this tendency - they have inertia. But do some objects have more of a tendency to resist changes than others? Absolutely yes! The tendency of an object to resist changes in its state of motion is dependent upon mass. Inertia is that quantity which is solely dependent upon mass. The more mass which an object has, the more inertia it has - the more tendency it has to resist changes in its state of motion.

· Mass is a scalar quantity

· The symbol for mass will be lower case “m”

· The units for mass are as follows:

MKS = kilogram (kg)

CGS = gram (g)

English = slug (slug)

Suppose that there are two seemingly identical bricks at rest on the physics lecture table. Yet one brick consists of mortar and the other brick consists of Styrofoam. Without lifting the bricks, how could you tell which brick was the Styrofoam brick? You could give the bricks an identical push in an effort to change their state of motion. The brick, which offers the least resistance, is the brick with the least inertia - and therefore the brick with the least mass (i.e., the Styrofoam brick).

A common physics demonstration relies on this principle that the more massive the object, the more that object tends to resist changes in its state of motion. The demonstration goes as follows: several massive books are placed upon the teacher’s head. A wooden board is placed on top of the books and a hammer is used to drive a nail into the board. Due to the large mass of the books, the force of the hammer is sufficiently resisted (inertia). This is demonstrated by the fact that the teacher does not feel the hammer blow. (Of course, this story may explain many of the observations, which you previously have made concerning your "weird physics teacher.") A common variation of this demonstration involves breaking a brick over the teacher's hand using the swift blow of a hammer. The massive bricks resist the force and the hand is not hurt. (CAUTION: do not try these demonstrations at home.)

Figure 4

 

Term That Used

Inertia is also known as Newton's first law of motion. In common usage, the term "inertia" is sometimes also used to refer to an object's momentum, or to describe its "amount of resistance to change" (which is technically the same as its mass). It is important to understand that these uses of the term are not the same as Newton's more fundamental definition of "inertia" as a principle of the way the universe works (which is not a measurable thing).

          The term of inertia also used in medicine field such as “clinical inertia”. Medicine has traditionally focused on relieving patient symptoms. However, maintaining good health increasingly involves management of such problems as hypertension, dyslipidemia, and diabetes, which often have no symptoms. Abnormal BP, lipid, and glucose values are generally sufficient to warrant treatment without further diagnostic maneuvers. These commentators focus on limitations in managing such problems in everyday practice. They term this "clinical inertia"-- recognition of the problem but failure to act -- failure of clinicians to initiate or intensify therapy when indicated.

 

2.                 Analysis Of Text Book Presentation

The Physics form 4 textbook stated that one of the learning outcome for this subtopic are by the end of the lessons, students would be able to explain what inertia is. According to the textbook inertia is the tendency of the object to remain at rest or, if moving, to continue its uniform motion in a straight line. The concept is illustrated by the figure 5.

Figure 5

The explanation about the figure 5 is “we are likely to fall backwards if the bus is starts suddenly from rest and if the moving bus stops suddenly, we are likely to fall forward”. The textbook also explains what causes the situation happen. It says “the bus moves suddenly from rest, our feet are carried forward but the inertia or our body tends to keep us at rest. This causes our body to fall backwards. When the bus stops suddenly, our feet are brought to rest, but the inertia or our body tends to continue its forward motion. This causes our body to fall forward”. We find that the example and the explanation given are quite clear but what happen if the bus moves with a very slow motion? Is the situation still the same? So, we think the example is not really enough to describe inertia that is happen in our daily life.

The textbook also illustrates the idea of relating mass and inertia, by the figure 6.

Figure 6

The explanation of the figure 6 that given, “the adult who has more mass will show more reluctance to change her state of rest or motion. This property of the mass of a body that resists change from its state of rest or motion is known as inertia. The larger the mass, the larger its inertia.”

Other than that, the textbook also gives keywords how to memorize inertia concept “an object in a state of rest tends to remain at rest” and “an object in a state of motion tends to stay in motion”.

It also state that the Newton’s first laws as “every object continues in its state of rest of uniform”.  The textbook used graphic to describe the idea of inertia phenomenon. There are two exercises given in this textbook the first one is about to gain an idea of inertia and the second one is to find out the relationship between inertia and mass. Also given is one critical and creative thinking question “ The massive oil tanker takes a long time to accelerate to its full speed and a few kilometers to come to a stop even though the engine has reversed its propeller to slow it down. Why?”  We find that the exercises are not enough to test student knowledge about the inertia concept.

Another book we have analyze is ‘Form 4 New Vision Physics’. In this book, it state that inertia is:

·         The reluctance of an object to move once it is at rest.

·         The reluctance of an object to stop once it is in uniform velocity.

·         The tendency of an object to remain at rest, or if moving with uniform velocity, to continue its motion in a straight line.

It also state that the term of Newton’s first law of motion is also called the law of inertia, and the Newton’s first law of motion paraphrased that every object will continue in its state of uniform velocity or at rest unless it is acted upon by an external force.

Below is other explanation about inertia that is contain in this book.

Figure 7 Motion of a car

Figure 8

 

Figure 9

 

·         As shown in Figure 9, when the lowest coin is struck with a steel ruler, the rest of the stack of coins does not collapse.

Figure 10 A jerk applied to the toilet paper

 

Figure 11 Ball bearing flies off after collision

 

Figure 12 Mass determine the amount of inertia

 

Figure 13 A more massive pail has more inertia

Figure 14 A bowling ball has more inertia than wooden bottles

Figure 15 A fat boy has greater inertia

 

·         Positive Effect of Inertia

(a)

                     (b)                                                 (c)

Figure 16 The positive effects of inertia

(a)   In order to dislodge ketchup from the bottom of a bottle, the bottle is normally given a jerk as shown in Figure 16 (a).

(b)   A sumo wrestler as shown in Figure 16 (b) who has a greater mass also has a greater inertia. He is harder to be toppled and normally he is likely to win a championship tournament.

(c)   The head of a hammer can be tightened onto the wooden handle by applying a knock on the handle as shown in Figure 16 (c).

·         Negative Effects of Inertia

(a)   The negative effects of inertia can be seen obviously in car accidents. When a car is suddenly stopped due to collision, the driver and passengers of the car will be jerked forward due to inertia. This causes injury or death to them. To overcome this problem, safety features such as seat belts, air bags and headrest are fixed in the car.

(b)   Furniture carried by a lorry normally is tied up together by string. When the lorry starts to move suddenly, the furniture are more difficult to fall off due to their inertia because their combined mass has increased.

Figure 17 To tie furniture together can increase the inertia.

 

We find that this ‘Form 4 New Vision Physics’ book gives more examples, this can help student understand more about inertia concept.

 

3.                 Student Alternative Conceptions About Inertia

Misconceptions greatly influence learning. Students may internalize new ideas, but if the learning is incorporated into incorrect assumptions or ideas, the learning is superficial and of doubtful value. Educational research has shown that students typically learn best by moving from the concrete to the abstract; learning is enhanced through the use of manipulatives and handson activities. Teachers can dramatically influence learning by providing constructive feedback and by maintaining appropriately rigorous expectations.

 

summary of students’ conceptual alternative

Telling or showing students the explanations that science uses may not change their beliefs. There are several strategies that can be used to facilitate a deeper understanding. Students need to become aware of their own preconceptions about a concept and expose these beliefs by sharing their ideas with other students in small groups in an uncritical environment to help them begin a deeper analysis of their experiences. They should be encouraged to make predictions based on their conceptions before activities begin. This will help students to begin to confront and test their beliefs and provide motivation for looking for other plausible conceptions.

Students need to have time to work toward resolving conflicts between their ideas and their observations, thereby accommodating new concepts. Students need opportunities to extend new concepts by trying to make connections between the new concept and other situations in their daily lives. Students should also be encouraged to go beyond these initial steps by choosing additional questions or problems related to the concept to expand their understanding. These strategies are used to organize suggested activities into the following groups: exposing beliefs, committing to outcomes, confronting beliefs, accommodating concepts, extending concepts, and expanding inquiry.

 

4.                 Conlusion

Studies shows that misconceptions greatly influence learning. We hope this analysis and literature review that discussed above will give more input to teacher or future physics teacher about inertia concept and can help them in planning teaching activities in the physics classroom especially in topic of Inertia.

 

 

 

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