Download Annotations of Practical Activities for Motion Area of Study

VCE Physics: A SAC task for Unit 3 Outcome 3
Annotations of at least two practical activities from a practical logbook
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Outcome 3
On completion of this unit the student should be able to investigate motion and related energy
transformations experimentally, analyse motion using Newton’s laws of motion in one and two
dimensions, and explain the motion of objects moving at very large speeds using Einstein’s theory of
special relativity.
To achieve this outcome the student will draw on key knowledge outlined in Area of Study 3 and the
related key science skills on pages 11 and 12 of the study design.
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Questions and considerations in running the pre-SAC experiments and the “in-class” SAC
The following are some things for the teacher to consider for this type of SAC, and also possible
suggestions (where relevant or applicable) have been made for the teacher’s consideration:
Questions:

Practical activities range from demonstrations, POE's, round robins of task, self-paced exercises,
formal experiments to extended investigations. Should this assessment task for the Motion Area of
Study focus on experiments? That form has been adopted for this document.

What does 'annotation' mean? Is it commentary and answers to questions as the experiment is being
conducted or is it done some time later?

How many experiments should be the focus of this SAC?

How should this SAC be implemented? (e.g. teacher provides a series of questions in relation to the
experiments completed, with student responses forming the basis of the “annotations” required for
this SAC)

Is it acceptable to bring in some of the Key Knowledge bullet points from the Special Relativity part
of this Outcome?
Considerations
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teacher could consider providing students with the objective(s), all materials/resources needed,
and the procedures to be used for each experiment; this will ensure “base consistency” in how an
experiment will be run, while also providing opportunities for students to offer suggestions to
improve the experimental setup, as well as responding to questions that form the basis of this
“annotations” SAC)
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students can work independently and collaboratively during the course of the experiment, but the
SAC is completed individually
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teacher could allow students to choose the format for displaying their results rather than providing
them with a table and headings, in order to allow the students to demonstrate their ability to record
and display results using appropriate conventions (including units of measure)
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by referring students to the procedure and results of their experiment in the SAC will give them a
context for demonstrating an understanding of errors associated with each experiment, rather than
simply recalling the key ideas relating to errors
At Least Two Experiments
Some possible experiments and questions which could form the basis of the annotations for this SAC are
shown in the table below. Many other suitable experiments can be undertaken by teachers.
An appendix at the bottom of this document provides some additional information.
Experiments
Questions that form a part of the Assessment?
Investigating Newton’s 2nd Law on an
Inclined Plane
- students will demonstrate their
understanding of forces in one and
two dimensions
- optionally students can explore the
concept of work done as the cart
moves up the incline
 Draw all the forces acting on the dynamics cart and
the mass.
 What happened to the magnitude of the acceleration of
the cart as the slope of the incline increased and
everything else remained unchanged? Explain your
answer with calculations.
 What happened to the magnitude of the acceleration of
the cart if the hanging mass increased and everything
else remained unchanged? Explain your answer with
calculations.
 Identify two specific sources of equipment error that
may have contributed to large percent differences
between the theoretical and experimental methods for
determining the acceleration of the system.
 Identify two specific sources of human error that may
have occurred in this experiment.
 How would you modify this experiment to determine
the effect that increasing the mass of the cart has on
the motion given to it by a constant force?
Projectile Motion (horizontal projection)
- students investigate motion in two
dimensions (including developing an
understanding of the motion of a
projectile in Earth’s gravitational
field)
- students will gain experience in
determining the range of a projectile
for different horizontal velocities
- students will gain experience in
calculating the initial horizontal for a
given range and vertical
displacement
 Write a definition for the term ‘projectile’.
 Discuss two methods for determining the horizontal
velocity of the object in this investigation.
 How does the range compare to the horizontal
velocity? Include a reference to your hypothesis (e.g.
how did the relationship between range and velocity
compare with your hypothesis?)
 What is the most important type of error in this
experiment? Give an example that applies to this
experiment.
 How would the launch velocity be different if the
mass of the projectile was greater than that of the
projectile used in the experiment? What about if the
mass was less than the object mass used in this
experiment?
 Explain, using a calculation what would happen to the
range of an object, and its time of flight, if the
projectile was launched with the same initial launch
speed, but at an angle of 30º to the horizontal.
Investigating Horizontal Circular Motion
- students will be investigating the
relationship between centripetal
force acting on an object moving in
a circle of fixed radius and the
period of its motion
- students will extend their
understanding to solving circular
motion problems on a larger scale
 Identify two physical quantities in this experiment that
you attempted to maintain constant for each of your
trials.
 Explain what is meant by the period of an object when
it is undergoing circular motion. Provide an example
calculation as part of your response to this question
(e.g. a calculation to the problem “If an object
revolves 50 times in 20 seconds, what is the period of
the object?”).
 Identify the formula that determines the magnitude of
the centripetal acceleration from the data that you are
able to measure in this experiment (e.g. students
should be able to measure radius ‘r’ of string and
determine the tangential speed ‘v’).
 Sketch a graph of centripetal force as a function of the
reciprocal velocity squared (i.e. graph of Fc vs 1/v2).
 Discuss the error that is introduced if the string is not
moving in a horizontal plane (i.e. the stopper is
allowed to sag). You should include specific reference
to the stopper’s weight and its effect on the tension on
the string.
 If the mass of the stopper were increased, describe
what would happen to the force needed to keep the
stopper in “orbit” if the tangential speed and radius
remained the same? How would the orbital period
change? Use calculations to support your answer.
 If the radius of the string was increased while
maintaining a constant mass and tangential speed, how
would the centripetal force change to compensate?
Use calculations to support your answer.
 Based upon your understanding of acceleration in a
horizontal plane, how would you expect that doubling
the speed of the object to affect the centripetal force?
 The concepts examined in this practical task can be
extended to satellite motion. Identify the cause of the
centripetal force of a communications satellite which
is in geosynchronous orbit about Earth. Note:
question(s) requiring students to undertake
calculations involving satellite motion could be
potentially added.
Energy Transformations (converting PE to
KE)
- using an inclined plane, students will
roll a dynamics cart down the incline
in order to investigate how the sum
of the cart’s kinetic energy and the
work done against friction compare
with the cart’s loss of potential
energy
 Explain the energy transformations that take place as
the cart rolls down the incline (responses need to refer
to the Law of Conservation of Energy?)
 Describe an experiment that you could perform to
determine if the mass of the cart has any effect on the
amount of energy required to overcome friction.
 If the cart was replaced by a block of wood on the
inclined plane, how would you expect the values for
-
kinetic energy and work done against friction to
change?
 What happens to the energy spent in overcoming
friction?
Conservation of Momentum
- students will gain an understanding
of momentum and the principle of
conservation
 If both carts have the same mass, describe the velocity
of each cart.
 When the connection between the two carts is
‘broken’, how do the forces exerted on each cart by
each cart’s spring compare?
 How does the speed of the cart with greater mass
compare to the cat with less mass?
 Explain what would happen to the momentum of the
two carts if the springs were stiffer.
 Identify the two most likely sources of friction that
could produce errors in this experiment.
 Discuss the consequences of the table (used to support
your experimental setup) not being perfectly level.
 This experiment can be used to simulate a rifle firing a
bullet. In the case of a rifle and the bullet, the bullet
attains a high speed, but the rifle does not. Explain the
reason for this.
 In the movie Eraser, an aluminium bullet is fired at
near light speed. If the rest mass of the bullet is
250gram, then calculate the relativistic mass if the
aluminium round was travelling at 0.8c.
Changes in Potential Energy?
 students measure and graph the
extension of a spring against force
 students drop of a mass from zero
extension and measure the maximum
extension.
 students use the Force vs extension
graph and the dropped distance to
generate energy versus distance graph
for elastic potential energy,
gravitational potential energy, then
determine graphs for total energy and
kinetic energy.
 Describe the force extension graph
 Use the graph to determine the spring constant
 Describe two ways to determine the spring potential
energy stored in the spring
 Not all of the gravitational potential energy of the
mass before it is dropped is transferred to spring
potential energy at the bottom of the fall. Suggest
where the missing energy may have gone.
 The graph of kinetic energy against distance can be
used to determine the extension where the speed is
greatest. Knowing the forces acting on the falling
mass explain where you expect this point to be.
Appendix
The level of equipment and other materials will vary between schools. In theory, all of these practical
activities can be run with basic equipment, or equipment which can be easily made, ideally by the
students. Further information in this regards can be provided.
Investigating Newton’s 2nd Law
Possible Equipment/Materials
- Dynamics cart
- Pulley and string
- Pulley clamp
- Weights (various)
- Ruler
- Ticker timer, photogate, video analysis,
Arduino microcontroller (or similar sort
of data collection or recording
equipment)
Horizontal Projection
Possible Equipment/Materials
- large marble or steel ball bearing
- tape measure or metre ruler
- stop watch (or video analysis software &
hardware)
- carbon paper (or similar) to measure landing
point of object
Investigation Horizontal Circular Motion
Possible Equipment/Materials
- Balance (for measuring mass)
- Glass tubing (or similar)
- Masking tape or alligator clip (to fix the
radius of rotation of the string)
- Metal washers
- Rubber stopper (or similar such mass)
- Stopwatch
- String (approx. 1 metre)
- Paper clip to support washers
Image credit: Taffel, Baumel & Landecker, 1966
Energy Transformations (converting PE to KE)
g
Conservation of Momentum
Possible Equipment/Materials
- two carts
- spring system to provide simulated
“explosion”
- ticker timer, video analysis, Arduino
microcontroller (or similar sort of data
collection or recording equipment)
http://cgscomwww.catlin.edu/sauerb/Ph12/PH12_Labs/PH12_Lab_17_Explosion_files/image002.jpg