Lesson Planning - SingaporeTeachersLearningCentre



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Postgraduate Diploma in Education (Sec)

Module QCP 521

Teaching of Physics II

Lesson Plan on Gravitation

Lecturer: A/Prof S. Springham

Submitted by

Gohel Amarsinh

054472J23

LG01

Subgroup 2

Lesson Planning

Topic: Gravitation – Newton’s Law of Gravitation, Gravitational Field Strength, g,

Class: Junior College Year 1.

Lesson Venue: Computer Lab

1. Introduction

The aim of this lesson is introduce to the student Newton’s universal law of gravitation. Through the use of applets and working through problems, the student will be taught to appreciate the law’s dependence on mass of objects concerned and separation distance of the objects. The student will also be taught to define g as gravitational field strength and explore its characteristics near Earth’s surface. The lesson will be conducted in the computer lab due to the extensive use of interactive IT to illustrate key lesson concepts.

2. Specific Lesson Objectives:

At the end of lesson, students should be able to:

a) relate gravitational field as a field of force and describe gravitational field strength as force per unit mass.

b) recall and employ Newton’s law of gravitation as [pic].

c) obtain, from Newton’s law of gravitation and the definition of gravitational field strength, the equation [pic]for the gravitational field strength of a point mass.

d) use [pic]to solve problems for the gravitational field strength of a point mass.

e) recognize g is almost constant near Earth’s surface, and is known as acceleration of free fall.

3. Prior Knowledge:

1) Knowledge of force,[pic].

2) Concept of gravitational acceleration, [pic].

3) Basic knowledge of how gravity works.

4. Learning Aids & Resources:

Set Induction: 1 marble

IT: i) 2 students to 1 PC terminal

ii) Powerpoint slides

iii) Internet websites for applets

Worksheets: Found in appendices.

5. Set Induction :

• Stand in front of the class and ask students if anyone thinks that the marbles will float in the air if thrown upwards. Then actually throw the marble to show that this will not happen.

• Ask students what is at work here, causing the marbles to fall downwards instead of upwards, so as to let them think about gravity and gravitational attraction.

• Help students to recollect and reconcile previous knowledge of what gravity is and how it works, thereby introducing the topic of Gravitation.

6. Instructional Strategies:

Introduction (Time allocated = 5mins)

The trigger activity serves to not only get the students’ attention to the lesson at hand but also serves to ‘remind’ students about the presence of gravity around us. Gravitational attraction is an always ‘on’ physical phenomenon, such that people tend to take it for granted and often neglect its presence. Hence the activity will let the student to start thinking about gravity and its effects.

The teacher will first aid the student in recalling previous knowledge about gravity by asking the students what they understand about it. This is to start of the lesson by linking the topic with what the students already know. This is in tune with Bloom’s Taxonomy’s initial stage of learning, where prior knowledge to the subject matter is first rehearsed.

Lesson Proper (Time allocated = 55 mins)

Worksheets (appendix) will be distributed to the students which will act as a guide for the students to follow the lessons. The students will work in pairs in front of a computer so that they can have easy access to the applets included in the lesson.

The teacher will first introduce the concept of a gravitational field as a region in space where a body exerts a force of attraction on another body. The key idea to convey to the students here is that gravitational attraction acts on every mass, and all around the mass. Gravitational attraction can be represented as field lines surrounding a body of mass. This is an extension of prior knowledge that students have about the properties of gravity. Gravitational field strength, g, is introduced to be defined as the force per unit mass acting on any object placed there.

Students will now access the following applet online:

.

The above applet, Gravity Lab, allows the students to play with gravity on a large scale, something which is not really possible in the laboratory. Students are able to measure the gravitational attraction between any two objects from a variety of selection that includes the planet Jupiter, a comet, a car and a bowling ball. Distances between the objects also can be varied in astronomical magnitudes. From working with this interactive applet, the students should be able to come to the conclusion that Newton’s law of gravitation depends on two factors: mass of the two objects concerned and the distance between the two objects and their relationships. This will make it easier for the students to assimilate and understand Newton’s law of gravitation when the teacher gives the formal definition of the law, stating that the force of attraction between any two mass is directly proportional to the product of the masses and inversely proportional to the square of their distance from each other, [pic]. This is in accordance with the next step of instructional progression from Bloom’s Taxonomy, which is the comprehension of the new knowledge acquired. Each term in the equation will be defined for the students. Properties of gravitational attraction will introduced to the students.

A comparison between the relative strengths of electric force and gravitational force is made. A scenario is provided to the students whereby they will be asked to give an intuitive answer as to how much mass would have to be added to one electron for a system of two electrons in a vacuum such that their gravitational attraction will counteract the forces of repulsion between them. This is to allow the students to make connections between two different forces in physics and will evoke their higher order thinking skills. However, a potential pitfall for the teacher here is that such a questioning might lead the students to asking deeper questions which the teacher might find difficult to answer. Hence, the teacher has to be well prepared in the subject matter so that he can answer the questions posed to him. A potential question that students might ask here: Since gravitational attraction is so much weaker than electric repulsion, why aren’t we attracted or repelled by objects around us? The answer: Our bodies and objects around us can be taken to be electrically neutral as there is the same number of negative and positive charges within each mass.

Following the progression in Bloom’s Taxonomy, now is the application stage. Hence, it is a good time for the students to try solving two problems to apply the newly acquired equation (problems 1 and 2 in the worksheet). This will aid them in learning how to employ the equation to solve problems. The final task in this section requires the students again access the applet, gravity lab, where each pair will design an experiment to plot out a graph depicting the relationship between gravitational force and separation of the two masses. This student-centered activity will apply some higher order thinking skills from the students and also help in developing cooperative learning within each student pair.

Next, the teacher will introduce to the student the definition of gravitational field strength, [pic]and show how the relationship can be derived from [pic] and[pic]. The students will be tasked to solve a problem (problem 3 in the worksheet) that calculates the value of g at various heights above the Earth’s surface. The students are then supposed to be able deduce that g is almost constant near the Earth’s surface. This is to allow the students to assimilate what they had just learnt and to try to deduce new information from this knowledge.

Lesson Closure (Time allocated = 10 mins)

The teacher will provide a short summary to what has been covered in the lesson so as to allow the students to recap and reinforce what they had learnt in the lesson today. Any doubts will also be cleared as the teacher allows questions to be asked or misconceptions to be clarified. Finally, homework for the day will be given. Question is of investigative nature that involves higher order thinking skills and is left as a pair work so as to enhance cooperative learning. This homework does not have a fixed answer and the teacher should consider a variety of answers, as long as they are physically logical.

7. Concept Map:

[pic]

7. Summary of Lesson Plan

|Time Frame |Activities |Materials |Rationale |

| |Introduction | | |

|5 min |Trigger Activity: Stand in front of the class and ask |Marbles |Attracts the students and lets them |

| |the class if marbles will float when thrown upwards. | |think about gravity. |

| |Verify by throwing one marble up into the air. | | |

| | | | |

| |Recalling previous knowledge about gravity by asking | | |

| |the students what they understand about it. | |Make students remember what they have |

| | | |previously learnt and link with what |

| | | |they are about to learn |

| |Lesson Development | |Microteaching Starts |

|5 min |Introduce the concept of a gravitational field as a |PowerPoint Slides |Provide necessary scaffolding of lesson |

| |region in space where a body exerts a force of | |ahead. Extends prior knowledge of |

| |attraction on another body. Gravitational field | |students about gravity. First S.I.O. |

| |strength, g, is defined as the force per unit mass | | |

| |acting on any object placed there. | | |

| | | | |

| |Students will access Gravity Lab applet online and | |Allow the students a hands-on experience|

| |explore the effects of gravity between different masses|Online Java Applet |with ‘gravitational attraction’ so as to|

|5 min |and different separation distances. | |make their own conclusions about its |

| | | |properties. |

| | | | |

| | | |This is the mathematical form of |

| |Introduce[pic], its formal definition and explaining |PowerPoint Slides |Newton’s gravitation law. Second S.I.O.|

| |the various terms in the equation. | | |

| |Properties of gravitational force are explained and | | |

| |some interesting facts about gravitational force is | | |

|17 min |introduced. A comparison between electric force and | |Help students link up various aspects of|

| |gravitational force is made. | |physics together. |

| |Students will be given two problems to solve. | |Students must be able to recognize this |

| | | |equation and be able to use the equation|

| | | |to solve problems. Second S.I.O. |

| | |Worksheet | |

| | | |Student-centred learning. Gives students|

| |Students, in pairs, are to design an experiment using | |opportunity to in use higher order |

| |Gravity Lab applet and utilize the graph plotting | |thinking skills and well as develop |

| |function to plot the graph of gravitational force vs. | |cooperative learning skills. |

| |separation distance to illustrate the relationship | |Microteaching Ends |

| | |Online Applet | |

| | | |Third S.I.O. |

| | | | |

| |Introduce the definition of gravitational field | | |

|13 min |strength as | | |

| |[pic]and show how the relationship can be derived from | | |

| |[pic] and[pic]. | | |

| |Students are to solve a problem applying [pic] and then| | |

| |make the deduction that g is almost constant near the |PowerPoint slides |Fourth and fifth S.I.Os. The problem is |

| |Earth’s surface. | |designed to lead students to make |

| | | |deductions with prior knowledge to |

| | | |obtain new knowledge. |

| | | | |

|15 min | | | |

| | |Worksheet | |

| |Lesson Closure | | |

|10 min |Short summary to what has been covered in the lesson. |PowerPoint |Give a chance for students to absorb and|

| |Provide chance for students to ask questions and clear |Slides |reconcile with what they have learnt. |

| |any doubts present. | | |

| |Homework for the day is of investigative nature and is | |Promote higher order thinking skills as |

| |left as a pair work. | |well as cooperative learning. |

| | |Worksheet | |

| | | | |

References

1) GCE ‘A’ Levels Physics Syllabus (2006)

2) Nelkon, M & Parker P. Adavnced Level Physics. Oxford: Heinemann Educational. (1998). Chap. 7.

3)

4)

5)

6)

Worksheet for Gravitation

1. Gravitational Field

Gravitational Field is a region in space where a body exerts a _______________ on another body. Such a region can be represented by ____________________. The lines of force are always directed towards _______________________.

Draw the gravitational field lines acting on the spherical body below.

[pic]

Gravitational field strength, g, at a point is defined as the force acting on per unit mass at that point.

g = [pic]

Gravitational field strength is a ______________.

2. Newton’s Law of Gravitation

Now, work in pairs and access the applet, Gravity Lab, from the website given below:



Click on Explore Gravity and do as the applet suggests: toy with the universe!

While exploring the applet with the various masses, try and see if you can deduce what physical quantities does gravitational attraction depend on.

1) _______________ 2) ________________

Newton’s universal law of gravitation states that, for any two mass in the universe, there exists a _________________ between the two masses that is _______________ to the ______________ and ___________

_________ to the ________________________________________.

Mathematically, the above statement can be represented as:

[pic]

M, m are _______ of the objects, r is the ________________________ _________and F is ________________________. The constant of proportionality, G, was determined by Newton to be 6.67 x 10-11 Nm2kg-2.

PROBLEM 1:

Calculate the gravitational force the Sun exerts on the Earth. Does the Earth exert the same force on the sun?

{Radius of Earth’s orbit: 1.50 x 1011 m; Mass of Earth: 6.0 x 1024 kg; Mass of Sun: 2.0 x 1030 kg}

PROBLEM 2:

Joseph has a body mass of 100 kg and Daniel has a body mass of 70 kg. If they were standing 2.0 m apart from each other, what is the force of attraction between the two bodies?

Back to the Gravity Lab

Access the applet for Gravity Lab again and enter into Explore Gravity. Now, work with your partner to design an experiment that will allow you to plot a graph depicting the relationship between the separation distance of the two masses and their mutual gravitational attraction. (Note: Only do for 5 pairs of values). Print out the graph and attach it to the back of your worksheet.

3. Gravitational Field Strength, [pic]

Derive the above expression for g using [pic] and Newton’s second law,

[pic].

Note:

1) Gravitational field strength grows _________ when one is increasingly further away from the mass producing the gravitational field.

2) The expression [pic] only applies for r greater than __________________________________.

PROBLEM 3: Calculate the gravitational field strength, g, at the following heights above the Earth’s surface:

1) 100 m; 2) 1 km; 3) 10 km. (Radius of Earth: 6400 km)

What can you deduce about the gravitational field strength, g, near the Earth’s surface?

HOMEWORK TIME!!!

Do the following assignment with your partner.

In the movie Independence Day, the alien race that came to invade Earth arrived in a mothership that was 1/4 the mass of our moon. It arrived to a stop about 36,000 km above the Earth’s surface, which is about 1/10 of the distance from Earth to our moon.

Based on the information given and any other that you feel necessary, make an estimate of the gravitational attraction of the mothership on our planet. Discuss what are the effects on Earth due to the presence of such a massive object at such distances.

Was it necessary for the aliens to shoot at us at all?

Appendix – Screen Captures of Gravity Lab Applet

[pic]

[pic]

Reflections

After my micro-teaching, I realized that gravitation is really not an easy topic to teach. I say this because I feel that there is a lack of teaching aids or models that can be easily brought into the classroom to show the effects of gravitational attraction. Unlike topics like electricity, heat transfer or pressure, where demonstrations can be carried out easily in class to introduce the concept or aid in the teaching, the same cannot be said for the topic of gravitation. This is due to the fact that classroom demonstrations of gravitational attraction between two masses are usually not observable (besides the fact that everything thrown into the air falls to the ground) due to the small masses that we are limited with. Thus, the next best avenue for getting a viable demonstration of gravitational forces that students can interact with is through the use of applets. I was glad to be able to find the Gravity Lab applet which I think is excellent in helping student learn about gravitational forces. The fact that students are able to interact with the applet on their own and not just watch a simulation makes it an added bonus. If I would teach this subject again in the future, I would most certainly employ the use of this applet. Given more time to prepare though, I would still like to explore possible ways of making a viable model to bring into the classroom. I had toyed with the idea of demonstrating gravitational forces by using a suspended sheet of cloth and place a mass such a weight-ball at the centre of the cloth. Depending on the mass of the spherical object placed, it depressions of varying depths. A marble can then be placed in its vicinity, which will roll towards the spherical mass, simulating gravitational attraction. However, I decided against it because this demonstration brings in the idea of space-time curvature by bodies of mass and that involves Einstein’s general theory of relativity, which is really beyond the students’ level at this stage.

I also realize that I have to be more prepared when I pose questions that involve higher order thinking skills as such questions tend to let students consider the subject matter in a deeper sense and hence they may have questions that are not routine or easy to answer. Thus I have to be prepared for such possibilities and anticipate the possible questions that students might pose so that I would be able to answer them. I would have to prepare a set of support questions as well to guide my students along in their thinking process.

Last but not least, extra care has to be taken when preparing PowerPoint slides. What you see on your laptop screen can turn out very different on the projected screen, thus visual clarity is very important. Otherwise, it is easy for the student to become disinterested in what I am teaching if they cannot see the slides clearly. Luckily for this lesson, I had planned it to be in a computer lab such that the students can access the slides and the applets on their computer screens. Another point to take note of is not to squeeze too much information into one PowerPoint slide otherwise it will be hard for the students to follow.

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Acts all around every mass in the universe.

Almost constant near Earth’s surface, known as acceleration of free fall.

Inversely proportional to square of distance of separation.

Directly proportional to product of masses involved

Gravitational Field

Strength,

[pic]

Newton’s Law of Gravitation, [pic]

Gravitational field

Gravitation

Mass

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