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Physics Lesson Plan

Topic: Introduction to Moment

In partial fulfillment of the requirements for

QCP 521 Teaching of Physics II

Lesson Plan

Topic : Turning Effect of Forces (Introduction to Moment)

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Duration: 70 minutes (double period)Target Class : Secondary 3 Express.

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

1. Describe the moment of a force in terms of its pivot, force applied and the perpendicular distance from the pivot to the line of action.

2. Describe some relevant daily life examples.3. Define and calculate moments using formula 4. State and apply principle of moments for a body in equilibrium to

solve problems.

Prior Knowledge : Before the lesson, students shall be able to:

1. State and apply Newton’s law of motion.2. Interpret and construct force diagram.3. Construct perpendicular lines from a point to a line.

New Concepts/Terms:

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Turning Effect of Forces

Moment or Torque

is also known as

0.25 m

Clockwise

Anti-clockwise

can be

[SI units: Nm]

calculated by

Learning Aids & Resources :

Set Induction : A half-metre rule

IT : i) PowerPoint slides and overhead projectorii) Video demonstration on seesaw candle

Non-IT i) Worksheets (Appendices A, B, C)ii) Whiteboard and markersiii) Wrenches

Hands-on : 21 sets of the following apparatus: a half-meter rule, a mass of 50g, a mass of 100g, string and scissors.

Set Induction :

Ask students to observe and spot the difference in the way you drop the half-meter rule, as the following diagram depicts. One is to hold the meter rule at two ends and let go both ends simultaneously to allow free fall. The other is to hold the meter rule at two ends and release only one end, so the rule swings down towards the other end.

Use this activity to introduce pivot and turning effect of forces (moment or torque)

Get a student (probably a big guy) to open the classroom door as he usually does. Then ask him to open the door by only pushing near the hinge. He will realize it is extremely difficult to do so. If the class is not convinced, ask a few more students to try.

Ask the class to identify the pivot in this case and note the turning effect of the push on the door. Get the class to see the difference is the distance from the pivot.

Introduce the concept of moment or torque.

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handhand

half-metre rule

Lesson Development :

1) Everyday applications

The trigger activity uses the simple action of door opening to let students appreciate physics in our life. And more daily examples (wrench, crane, can opening etc) are introduced later to bring relevance of moment to the classroom.

2) Student participation

This will be a student-centred lesson whereby the class works in pairs to investigate the principle of moment. They will be given the necessary apparatus and worksheet (Appendix B) to deduce the relationship between clockwise moment and anti clockwise moment. Some students will also present their solutions to some problems on the board. This helps to keep the students on task and build up their confidence.

3) Experimental activities

The exploration activity on principle of moment provides hands-on experience and promotes inquiry thinking to enhance students’ learning.

4) Collaborative learning

After each pair has done the investigative activity, they will share their findings with the class and answer any questions pertaining to their findings.

5) IT – Interactive multimedia

The lesson will use PowerPoint slides as visual aides and show a video demonstration of seesaw candle to illustrate the principle of moment.

Lesson Closure:

Get the class to reflect on their learning and share with the class. Summarize the main objectives of the lesson.

References:

GCE ‘O’ Levels Physics Syllabus (5052) Video demonstration of seesaw candle http://teachersportal.nie.edu.sg/kcyap/Physics2002/O

%20Level/Turning%20Effect%20of%20Forces/Demo%206%20-%20CG%20-%20Candle%20See%20Saw/candleseesaw.mpg

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Lesson Plan Proper

Microteaching session is highlighted in italics.

Time Frame (min)

Teaching/Learning Activities Materials Rationale Key questions

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Induction Activity:

Ask students to observe and spot the difference in the way you drop the half-meter rule. One is to hold the meter rule at two ends and let go both simultaneously to allow free fall. The other is to hold the meter rule at two ends and release only one end, so the rule swings down towards the other end.

Get a student (probably a big guy) to open the classroom door as he usually does. Then ask him to open the door by only pushing near the hinge. He will realize it is extremely difficult to do so. Ask class to think of some daily life examples of moments.

Show two wrenches, one with long arm, the other with short arm. Ask students which wrench would they choose to unscrew a bolt.

Half -Meter Rule

Blackboard and marker

Wrenches

By comparing two different types of falling, it introduces pivot and turning effects of

forces to the students.

This simple everyday example brings relevance of moments to

our life and get students examine the rationale behind.

What’s the main difference in the way I drop the rule?

How would you describe the motion of the rule?

What has changed in these two different ways of opening the door?

Could you identify the pivot in this case?

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Development of Concepts:

Definition and Calculation of Moments

1. Introduce the definition of moments (formula and units), stressing on the meaning of “perpendicular distance”, and comparing with the definition of work done. Go back to the examples of two wrenches with

Through comparing to formula of work done, it promotes lateral

thinking and linkage to prior

Have you seen the formula somewhere else? Also involves

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Time Frame (min)

Teaching/Learning Activities Materials Rationale Key questions

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different length and door-opening activity, ask students to apply the formula to explain that the moment required to turn an object is fixed, while distance is longer, force required will be less.

2. Show some daily life examples of moments, get students to identify the pivot, the force and construct the perpendicular distance. During the construction, the line of force can be extended if necessary. Can ask students to present their answer on the transparency.

3. Using wrench example, ask students to choose the direction to apply force on the wrench. At the same time introduce clockwise and anticlockwise moments using the wrench example.

4. Let students try some simple questions on calculation of moments. Ask a few students to present their answers on the board if time allows. And use the working examples to investigate moment about different points, students will realize the importance of identifying the pivot.

Principle of Moments

1. Recall the concept of clockwise and anticlockwise moments, show pictures of cranes to let students ponder how to balance the moments.

Whiteboard and markers

Worksheet appendix A

(OHT)

Wrench, Clock (in classroom)

Whiteboard and markers

Worksheet appendix C

PowerPoint slides

knowledge.

Make sure students understand the perpendicular distance is

from pivot to the line of force by showing the examples.

Let students realize that force and distance will influence the

outcome of turning effects.Use clock to illustrate the

direction of moments.

It’s easier for students to visualize and understand using

numerical examples.

Visual aides to show real life application of moments.

force and distance? Why do you feel it’s

harder to open the door if you push near the hinge?

Is this the correct way of drawing perpendicular distance? (non-example)

Which direction shall I apply the force? F1, F2 or F3?

What happened if I change the question to “find the moment about point B instead”?

Have you ever noticed how a crane keeps its balance?

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Time Frame (min)

Teaching/Learning Activities Materials Rationale Key questions

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2. Inquiry Activity (Pairwork)Give clear instructions and expectations before grouping the students. Ask one student to tie the string at 25 cm mark to keep the rule balanced. Then put the 100g at one side of the string and the 50 g on the other side to keep the rule balanced. The other student fills the data table in the worksheet to record down the mass and the corresponding distance. Let the students share their findings and induce the principle of moments.

3. Ask the students to draw the force diagram of their experiment. Highlight the presence of gravitational force on all objects on earth. If the gravitational force is passing through the pivot, no moment is resulted due to zero distance. Relate the previous crane example and ask students to apply the principle to explain how the crane keeps its balance. Show the video of seesaw candle to get students explain the observation.

4. Show one working example using principle of moments. Ask students do a few more questions, in increasing difficulty.

PowerPoint Slides

Half-meter rule, string, 50g and 100g masses.

Worksheet appendix B

Worksheet appendix B

Video clip (Seesaw Candle)

Worksheet appendix C

The inquiry and induction approach is taken here to let

students investigate the principle of moments themselves. This is to promote a sense of ownership

towards students’ learning.

Pointing out students’ common mistakes helps them to avoid making the same mistakes.

Practice to reinforce the concept.

Is there any pattern you have recognized?

Are these all the forces present on the rule?

Why is the candle seesawing?

5 Closure:

1. Let students write down their reflection of the lesson. Then ask a few students to share what they have learnt from this lesson.

Encourages reflective learning and makes learning more

conscious and visible to the students.

What are the most important things you have learnt in this lesson?

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Time Frame (min)

Teaching/Learning Activities Materials Rationale Key questions

2. Summarize the concepts taught in this lesson: the definition of moments, its application in our daily life, the principle of moments.

3. Ask students to finish the questions in the worksheet as homework. Tell them that you will check their work in the next lesson.

Microteaching Reflection

Through the process of micoteaching, I have learnt the following points:

Be very thorough and confident about the content I am teaching. I realized that students could ask any questions related or non-related to the topic you are teaching, thus it’s essential to be very familiar with the content and prepare beyond the requirement of the syllabus. For example, only by observing my colleague’s microteaching, I realize some of my misconceptions, like speed of wave is only affected by the medium it is traveling, not by the wave’s frequency or wavelength as the equation may have suggested .

Listening to my colleague’s microteaching, I realize the importance of student-centred teaching. There are various ways to engage the students, like doing investigative activities, getting feedback from the students, showing video clips or simulations. In comparison, real life demonstration is more effective to bring the message across than a demonstration video clip.

Lesson plan helps greatly in structuring the lesson and smooth transition of the contents. It makes me conscious to decide the flow of the ideas so that students can follow the concepts and don’t get lost in the lesson. The lesson plan also helps me to identify the rationales behind each teaching activities, so that it’s clear to me which skills are not developed in the lesson and helps me to improve my teaching approaches.

In demonstration or illustration of concepts, it’s important to convince the students what you are saying is true, like if you have two magnets, you tell students one magnet is stronger than the other, to verify this, you show that the stronger magnet can attract a lot more paper clips than the weaker magnet. This helps students to clear their doubts and believe in what they are seeing.

I also note that if the demonstration produces quite a few results or you have quite a few questions related to the demonstration, it’s beneficial to record the observations or students’ answers on the whiteboard. This helps students to stay focused and also makes it much easier for you to refer to while illustrating the concepts.

I find the microteaching very helpful and beneficial, it opens my mind to various ideas of teaching physics topics and brings my attention to some common pitfalls. Through sharing and observation, we learnt each other’s strength and weakness.

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Appendix A Daily Application of Moments

Draw on the following diagram the pivot, the force and the perpendicular distance.Indicate whether the direction of the moment too, clockwise or anticlockwise.

lid

Tin can

spoon

effort P

effort

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Appendix B Investigation on Principle of Moments

Objectives: To analyze the effects of clockwise and anti clockwise moment To investigate the conditions to keep an object at equilibrium To induce the principle of moments

Apparatus: A half-metre rule A mass of 50g and a mass of 100g Some strings

1. Use the string to suspend the rule, make sure the rule is balanced. At which marking shall you tie the string?

2. Place the 50g mass anywhere on one side of the rule, what effect does it have on the rule? What’s the moment and the direction of the moment? Show your working clearly.

3. Place the 100g mass on the other side of rule to keep the rule balanced. At which marking shall you put the 100g for this to work? What’s the moment produced by this 100g mass and the direction of the moment? Show your working clearly.

4. Repeat step 2-3 five times and record the data in the following table. g = 10m/s2

Weight of 100g mass __________________ Weight of 50g mass____________________

1 2 3 4 5 6

Data set

Distance of 100g mass from pivot

(cm)

Direction of moment produced by 100g

mass about the pivot

Moment produced by 100g mass about the

pivot (Nm)

Distance of 50g mass from pivot

Direction of moment

produced by 50g mass about the

pivot

Moment produced by

50g mass about the

pivot (Nm)

1

2

3

4

5

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5. Did you observe any pattern in the values you obtained from column 3 and 6? How about column 2 and 5?

6. Based on your investigation, what do you think are the necessary conditions for an object to be balanced (in equilibrium)?

7. Draw a force diagram of the experiment while the rule is balanced with 100g and 50g masses on it. Indicate ALL forces acting on the rule.

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Appendix C Exercises on Turning Effect of Force

1. Find the moment of the exerted force about the pivot O for the following situations, show your working clearly.

2. Find the moment of the exerted force about the pivot O for the following situations:

Hint: use trigonometry

O

5 N

1.5 m

O

5 N1.5 m

O

5 N

1.5 m

0.75 m

O

5 N1.5 m

1.3 m

O1.5 m

10 N

30

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3. A metre rule with uniform weight is balanced at its centre by two weights, X and Y as shown in the figure below. If the weight of X is 40 N and the weight of Y is 60 N, find the distance of weight Y from the support.

4. A metre rule with uniform weight is balanced by a weight, Z as shown in the figure below. If the weight of Z is 40 N and the weight of the ruler

40N 60N

0.3 m d

40N

0.1 m 0.25 m

W

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5. A man of mass 72 kg stands on one end of a see-saw. Two children sit on the opposite end as shown in Figure 6. If the pivot is assumed to be smooth, which of the following gives the correct combination of the masses of the children that are able to balance the man?

Child A Child B

A 40 kg 50 kgB 45 kg 42 kgC 50 kg 40 kgD 54 kg 54 kg

6. A painter of weight 1000N stands 1.0m from the left-hand end of a uniform plank which is 5.0m long and weighs 800N. The plank is supported by two trestles each 0.5m from the opposite ends. The diagram below shows the two upward forces P and Q acting on the plank due to the trestles.

7.8.9.

(a) Complete the diagram above to show any other forces which are acting on the plank. Name each of these forces. (b) What is the magnitude of the total downward force exerted on the trestles?(c) What is the magnitude of the total upward force exerted by the trestles on the plank?(d) By taking moments about the left trestle, calculate the upward force exerted on the plank by the other trestle.

1.50 m

1.00 m

0.50 m

Man

AB

0.5m0.5m

QP

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