Topic: Mass, Weight and Density

QCP521 MicroteachingPage 1

Subject: Physics

Topic: Mass, Weight and Density

Level: Secondary 3 Express Class

Class Ability: Average

Time: 2 periods (70min)

Pre-requisite Knowledge:

1. Students have some background knowledge on the difference between mass and weight
2. Students have some background knowledge on density
3. Students have basic algebraic manipulation in Mathematics

Specific Instructional Objectives

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

1. State that mass is a measure of the amount of substance in a body
2. State that weight is a force that is due to the gravitational pull on the body
3. Identify the instruments required to measure mass and weight
4. State the relationship weight = mass x acceleration due to gravity
5. Compare and contrast the difference between mass and weight
6. Apply the relationship between weight, mass and gravitational field strength to new situations or to solve related problems
7. Define Inertia of a body as the reluctance to start moving when it (the body) is at a state of rest or the reluctance to stop moving when it (the body) is at a state of motion
8. Briefly explain why a massive body is harder to start moving or stop moving with the relationship that the bigger the mass, the greater the force required to overcome its inertia and vice versa.
9. Define density as mass per unit volume
10. Calculate density using the relationship density = mass / volume
11. Tell whether an object will float or sink by calculating the density and comparing it with the density of water or other liquids
12. Apply the relationship between density, mass and volume to new situations or to solve related problems

New terms

• Acceleration due to gravity
• Inertia

Learning aids/resources

• Spring balance
• Electronic balance
• Raw Eggs
• package’ containing a rock, a mass of 20g, a book no bigger than their textbook, a tabletop calendar and a block of wood.
• 2 containers of equal size, one filled with objects, one empty, wrapped them with a paper so that students cannot tell what is inside
• Websites:

Lesson Development:

This lesson will be conducted in the lab.

Introduction (mass and weight)

I will start off the lesson by having the students work in groups of 4 and conduct a simple activity of mass and weight measurement. Each student will be given a worksheet and the group as a whole will receive a ‘package’ containing a rock, a mass of 20g, a book no bigger than their textbook, a tabletop calendar and a block of wood. The activity will be guided and not entirely student-centered. It will not take a long time, as this is meant to be a short introduction.

Development (mass and weight)

Using powerpoint slides, I will guide the students to do part of their worksheets. The concepts of mass and weight, the instruments to measure them, their SI units will be discussed. They will then have a short discussion among their groups about the differences between weight and mass. We will then discuss these differences as a class.

Introduction (Inertia)

We will begin the next section on inertia with another simple activity. Each group will be given an egg and every member of the group gets to try spinning the egg and stopping it. The students will be asked what are their observations.

Development (Inertia)

The concept of inertia will be discussed. Real life experiences of inertia will be brought out for discussion as well. Develop the concept that the greater the mass the greater the inertia. The mode of presentation is still powerpoint and students will continue to fill up their worksheet.

Density (Introduction)

The story of Archimedes will be brought up using the following website: . This is basically about Archimedes helping his king solve the problem of find out whether the crown was purely made of gold. I will not cover the whole story; instead, I will stop at the part where the king posted the problem to Archimedes. (I will stop here)

Development (Density)

I will go through with the class using the example of packing something into a fixed volume. Then I will define what is meant by density and show them how this definition is expressed in mathematical form. I will move on to asking the students to calculate the density of some objects listed down on my slide and determine whether the object will sink or float using their daily experiences. After which, I will ask them what is significant about the object that floats or sink when they compare the density of water.

Next I shall show them a video of how different objects float on different objects floating on different kinds of liquid from this website (under sinking objects).

The groups will get together and discuss how to solve Archimedes problem with the remaining time and write their solution in a mahjong paper. They will be required to present their solution to the class the next lesson.

Consolidation

The last 5 minutes will be used for consolidation. A concept map will be shown to the class, and a summary of what is learnt will be given.

Lesson Plan Time Table

Teaching/Learning Activities / Duration / Resources
Introduction (mass and weight)

Measuring mass and weight

Instructions for the students:
They are to work in groups of 4. Each bench is to collect a package containing a rock, a book, a mass of 20g, a calendar and a block of wood. The electronic balance and the compression balance (with newtons scale) will be introduced to them. Instructions will be given on how to use them. They are to record their readings of each object on the worksheet, with particular note being taken on the units. The units of each object should be read off from the instruments. Other instructions including how to facilitate movement will be given.
Development (mass and weight)

The concept of mass

The students will fill up the worksheet as the teacher explains the concepts.
Question:
Which instrument do you think is used for measuring weight and which is for mass? (Pause) Why is that so? (Pause) There is no need to answer this question now, as the answers will be covered later in the class.
Show PPT slide 1. Define what is mass, the units use for measuring mass and the conversion factor.
Question:
What is 1 tonne in g? (Pause) Allow time for students to do some simple calculations
Question:
If mass is in kilograms what about weight? How come we always say our weight is in kg? Are we measuring our mass? (Pause) Do not answer this question first, let the students think about it and then answer it after the topic of weight is covered.
Measuring mass
Show PPT slide 2. Let the students know that the instruments used for measuring mass are beam balance and electronic balance.

The concept of weight

Show PPT slide 3. Define what is weight and its units. Relate the Newton’s 2nd law, Force = mass x acceleration with Weight = mass x acceleration due to gravity.
Question:
Since weight is a force, it is also a vector, ask the students where do they think weight is pointing to? (Pause) The answer is ‘downwards’ towards the Earth.
Show PPT slide 4. Briefly go through the value of g in different planets. Most importantly, highlight that g on Earth is 9.81ms-2, and usually we take the value as 10ms-2 in our calculation. Indicate that we weight differently on different planet.
Question:
Does our mass changes when we are in different planets? (pause) The answer is no, because mass is the amount of substance in our body and since the substance in our body remains constant while in other planets, our mass should not change. Let the students understand that our weight changes because the gravitation pull in different planets are different.

Measuring weight

Show PPT slide 5. Let the students know that the instruments used for measuring mass are spring balance and compression balance.
Now that the concept of weight is covered, explain to student that we use kg as a unit for weight loosely because of convenience and convention.

Comparing weight and mass

Show PPT slide 6. Ask the students to form back their groups and discuss the differences between mass and weight.
After the discussion, go through the differences as a class. Get groups to tell the teacher what differences they have came out with. If they miss out any, the teacher will prompt or give them the answers. (depends on time)
Introduction (Inertia)
Show PPT slide 7. Get the bench leader to collect a raw egg. Each member will get a turn to try this. Give the egg a spin, put a finger on top of the egg to stop it. Lift the finger quickly. Ask them what they observe. For this part, the teacher may need to demonstrate how it is done. Do it in such a way that after the finger is lifted, the egg does not stop spinning straight away but slow down.
Development (Inertia)
Concept of inertia
Show PPT slide 8. Define what is inertia.
Show PPT slide 9. Ask the students which of the following is easier to push or stop? The beast or the child? They should give the right answer. Follow up by explaining that greater the mass the greater the inertia.

Introduction (density)

To bring in the story of Archimedes
Start by accessing the website:
Summarize the main points written on the each page and basically read the story of Archimedes and his King’s problem to them.
Stop once the teacher reaches ask the class to think about the problem that was posted to Archimedes then tell them that we will return to solve the problem later.

Development (density)

An analogy/example of the concept of density

Show PPT slide 10. Bring out the 2 containers and ask them whether they can tell the difference between them. (Pause)
Have one student stretch his/her hand and put the 2 containers on each of his hand, then ask him/her what differences are there. Reveal the content of the containers.
Bring in the concept of density by telling the students that if more objects are being pack into a box of same volume, it is denser than the other box that has lesser objects.
The concept of density
Show PPT slide 11. Define density and its units. Ask them to recall that density = mass/volume which they had learnt in their Sec 1 science. Also teach them how to use ‘my dear valentine’ to remember the density formula.

Floating or sinking of objects in various liquids

Show PPT slide 12. Ask the students to calculate the density of the various objects listed. The mass and volume are given to them.
Ask them to determine whether the object will sink or float and placed in water and why do they think this is so by comparing the density of the various objects with water. (Pause)
Explain to them that if the object has a density greater than water, it will sink and if it is lesser than water, it will float.
Show them the video on sinking and floating objects on various substances.

Archimedes Problem

Show PPT slide 13. Help the students recall the Archimedes’s problem, and get them into their groups. Distribute mahjong paper and markers, have the students to write their solution to solve Archimedes problem on the paper.

Closure

Show PPT slide 14. Recap the concept of mass, weight and density using the concept map. / 10min
5mins
2 min
10 min
2 min
10 min
5 min
5 min
2 min
4 min.
1 min
10 min
14 min
5 min / Worksheet
Objects
Electronic and compression balance
Powerpoint
Worksheet
Powerpoint
Worksheet
Powerpoint
Worksheet
Powerpoint
Worksheet
Powerpoint
Worksheet
Raw Eggs
Powerpoint
Worksheet
Powerpoint
Worksheet
Website
2 containers
Powerpoint
Powerpoint
Worksheet
Powerpoint
Worksheet
Powerpoint
Mahjong paper
Powerpoint

Microteaching Reflections

The comments that I received were the lesson was very smooth and the concepts were well developed. Perhaps I could have asked questions that require higher order thinking skills regarding sinking and floating objects.

The use of the Archimedes story was praised by my fellow classmates and I decided to go a step further by asking the students to do a group work on solving Archimedes problem. It would also have been better if I zoom into the microscopic view when comparing density of different objects, how closely pack the molecules are and so on.

The microteaching has taught me to constantly prompt students questions during the lessons to test their understanding and also spur them to think more. It has also made me think of different ways of teaching students the same concept.