The following is a summary of inertia that can be used for a grade 12 class.

1. Molaba LE 201416296 17-MARCH-2017
UNIVERSITY OF JOHANNESBURG
University of Johannesburg
Department: Science and Technology Education
Title:…………………….Writing a script for inertia…………………….
Full name:………………Molaba Legagarele Ernest………………..............
Student number……………….201416296…………………………..............
Course:………………Methodology for Physical Sciences………….............
1. Plagiarism is to present someone else’s ideas as my own.
2. Where material written by other people has been used (either from a printed source
or from the internet), this has been carefully acknowledged and referenced. I have used
the Geneva Convention for citation and referencing. Every contribution to and quotation
from the work of other people in this essay has been acknowledged through citation and
reference.
3. I know that plagiarism is wrong.
3.1 I understand what plagiarism is and am aware of the University’s policy in this
regard.
3.2 I know that I would plagiarise if I do not give credit to my sources, or if I copy
sentences or paragraphs from a book, article or Internet source without proper citation.
3.3 I know that even if I only change the wording slightly, I still plagiarise when using
someone else’s words without proper citation.
3.4 I declare that I have written my own sentences and paragraphs throughout my
essay and I have credited all ideas I have gained from other people’s work.
4. I declare that this assignment is my own original work.
5. I have not allowed, and will not allow, anyone to copy my work with the intention of
passing it off as his or her own work.

2. Molaba LE 201416296 17-MARCH-2017
UNIVERSITY OF JOHANNESBURG
Class, today we will learn about inertia. We experience inertia in almost every day of our life
without realizing it. This is because the concept is quiet abstract to witness. Let us refresh our
brains on the chapter of forces by discussing these questions: A) If you are travelling in a
vehicle at a constant speed, what happens to your motion when the driver applies the brakes on
the vehicle? B) Imagine, on the same floor horizontally so, if you push a box of 4 kg, and
then push a fridge of 208 kg, which one of the objects will accelerates more than the other?
Why is this the case? (Assume you apply an equal amount of force in the two case.
Question A.
You will agree that before the application of the brakes on the
vehicle, you were also travelling with the same speed of the vehicle
in the same direction of the vehicle. The application of the brakes
applies a force on the vehicle and you. This force is the one that is
responsible to changes the initial speed of the vehicle and yours.
Hence the vehicle will decrease in speed, so will you. However, you
will still want to lean forward a little bit as the brakes are applied.
This is because you resist a change in motion brought about by the
force of brakes, as the results we say that you have inertia. This
implies that if it wasn’t for the brakes, then you would still be
travelling at that constant speed of the vehicle without having to lean
forward.
F (brakes)
When the brakes are
applied on the vehicle,
the car accelerates in
the opposite direction
of motion. Leaning
forward is an indication
that you still tend to
conserve your initial
motion before the
application of brakes.
Question B.
It becomes easier for you to push the 4 kg box across the floor
than it is to push a 208 kg fridge. This is due to a relatively less mass
of the box than the fridge. As such, the fridge has a greater tendency
to remain at rest, (not move) than the box. Thus, we say the fridge
has more inertia than the box. Class, by now we should have an idea
of what inertia is.
Less mass,
Less inertia
More
mass,
More
Inertia
Inertia is the natural tendency of an object to remain at rest or in the state of motion at a non-
changing velocity. The quantitative measure of this tendency equals the mass of that object.
“This implies that inertia is measured with the SI units of kilogram (kg)” (Cutnell, 2014, p.86).
4kg
box
FRIDGE
208 kg
Definition of Inertia

3. Molaba LE 201416296 17-MARCH-2017
UNIVERSITY OF JOHANNESBURG
To gain a better understanding of inertia, imagine you put your soccer ball on a horizontal level
ground. You would agree with me that the ball will remain on the ground at that point until
otherwise kicked. The ball has a tendency of remaining at rest until it is disturbed. This is
referred to as the Inertia of Rest. Consider another example where a box slide across a
frictionless floor. The box will sustain its motion (keep moving at a constant velocity) until it
is acted upon by another force. What will happen if the box cross over to a rough floor? It is
obvious that the box will decreases in velocity until it comes to rest. The box changes its state
of motion due to the presence of another force acting on it. The box would still be travelling at
the constant velocity if it wasn’t for the frictional force it experienced on that rough floor simply
because it has the tendency to reserve its state of motion called Inertia of motion.
Classify the following instances as the results of Inertia of Rest or Motion
1. A balloon will rise indefinitely in the absence of gravitational force
2. When you travel in a train and throw an apple vertically upwards, it returns back to
your hand irrespective of the train’s motion.
3. A relatively larger net force is required to change the velocity of a vehicle than of a
bicycle.
4. The swirling of tea in a cup continues even after the stirring is stopped.
5. If pulled quick enough, “a table cloth can be removed from underneath the plates
without disturbing them” (Halley, 1960, p.230).
1.  In this case a gravitational force opposes the state of
motion of the balloon, hence in its absence the balloon would
rise indefinitely due to Inertia of Motion.
A rising balloon
Distinguish between types of Inertia
Class
Activity 1
Class let us discuss the solutions to Activity 1

4. Molaba LE 201416296 17-MARCH-2017
UNIVERSITY OF JOHANNESBURG
2. With the train moving at a particular velocity, the apple
also assumes an equal velocity of the train, that is an equal
speed and direction. Hence once the apple is thrown upwards,
it still travels horizontally as well as the results of Inertia of
Motion. The apple moves
horizontally.
3. A vehicle with a greater mass has a greater tendency to
remain at rest than a bicycle with a smaller mass. “The vehicle
requires more net force because of Inertia at Rest” (Cutnell,
2014, p.86).
Bicycle with less mass
Massive vehicle
4. The tea continues to swirl because of Inertia of Motion.
It only stops because it collides with the walls of the cup.
5. The plates will experience almost no external force if the
cloth is pulled quicker. Hence the plates will remain
undisturbed due to their Inertia of Rest.
Removing the table cloth
from underneath the plates
Class did you know that Galileo Galileo used the concept of inertia to predict that the earth
could be in motion (moving)? “He also used inertia to explain why we do not feel the motion
of the earth and why objects falling on the surface of the earth move together with the earth”
(Verma, 1999, p.124).
DID YOU KNOW?

5. Molaba LE 201416296 17-MARCH-2017
UNIVERSITY OF JOHANNESBURG
Class, from what you have learnt from our lesson today, what is the implication of Inertia?
 Inertia implies that a force is not required to sustain a state of motion of an object, but it is
there to change the state of motion instead.
1.  Inertia is the natural tendency of an object to either remain at rest or to continue
being in a linear motion at a constant velocity, that implies a constant speed in the
same direction.
2. Objects will remain at rest until they are disturbed by unbalanced forces.
3.  Objects will continue with their state of motion unless otherwise acted upon by
unbalanced forces.
Home Activity 17 March 2017
1. Define the term Inertia.
2. Distinguish between Inertia of Rest and Inertia of Motion.
3. Classify the following as Inertia of Rest or Inertia of Motion.
3.1 When you jump off a moving train, you fall forward.
3.2 When our vehicle jerk off, we lean backwards.
3.3 Objects always fall back to the centre of the earth.
The end!
SUMMARY
THE FUNDEMENTAL IMPLICATIONS OF INERTIA

6. Molaba LE 201416296 17-MARCH-2017
UNIVERSITY OF JOHANNESBURG
REFERENCE LIST
Cutnell, John D & Kenneth W.Johnson. (2013). Introduction to Physics.
Haliday David, Robert Resnick and Jearl Walker. (1960). Fundementals of Physics.
Nathaniel Lasry, Elizabeth Charles, and Chris Whittaker, (2014, April). When teacher-
centered instructors are assigned to student-centered classrooms [Journal] // PHYSICAL
REVIEW ST PHYSICAL SCIENCE EDUCATION RESEARCH. - p. 14.

7. Molaba LE 201416296 17-MARCH-2017
UNIVERSITY OF JOHANNESBURG
Rubric for Assignment 3: Writing a script for inertia
1 2 3
Quality of writing There are many errors
in spelling, grammar
and punctuation. The
script is difficult to
read.
There are few
errors in spelling,
grammar and
punctuation. The
script is
understandable
There are no errors in
spelling, grammar and
punctuation. The script is
clear and concise.
Use of visual
representation
Minimal effort
made to make
presentation
visually appealing
Has some visual
appeal, but the
quality can be
improved
Strong visual appeal
that aids
understanding
Use of examples Examples are
inappropriate to the
concept
Good examples,
but it is not
applied
effectively
Effective use of
examples
Quality of
explanation
Explanation is not
scientifically correct
and can lead to
misconceptions
Explanation is
scientifically
correct, but it can
made more clear
Clear explanation that
supports conceptual
understanding