# Physics

### Rationale/Aims

Physics is a fundamental science that endeavours to explain all the natural phenomena that occur in the universe. Its power lies in the use of a comparatively small number of assumptions, models, laws and theories to explain a wide range of phenomena, from the incredibly small to the incredibly large.

### Structure of Physics

In Physics, students develop their understanding of the core concepts, models and theories that describe, explain and predict physical phenomena.

### Links to Foundation to Year 10

The Physics curriculum continues to develop student understanding and skills from across the three strands of the F-10 Australian Curriculum: Science. In the Science Understanding strand, the Physics curriculum draws on knowledge and understanding from across the four sub-strands of Biological, Physical, Chemical and Earth and Space Sciences.

### Representation of Cross-curriculum priorities

While the significance of the cross-curriculum priorities for Physics varies, there are opportunities for teachers to select contexts that incorporate the key concepts from each priority.

## Unit 3: Gravity and electromagnetism

### Unit 3: Gravity and electromagnetism Description

Field theories have enabled physicists to explain a vast array of natural phenomena and have contributed to the development of technologies that have changed the world, including electrical power generation and distribution systems, artificial satellites and modern communication systems. In this unit, students develop a deeper understanding of motion and its causes by using Newton’s Laws of Motion and the gravitational field model to analyse motion on inclined planes, the motion of projectiles, and satellite motion. They investigate electromagnetic interactions and apply this knowledge to understand the operation of direct current (DC) and alternating current (AC) motors and generators, transformers, and AC electricity distribution systems. Students also investigate the production of electromagnetic waves.

Contexts that could be investigated in this unit include technologies such as artificial satellites, navigation devices, large-scale electrical power generation and distribution, motors and generators, electric cars, synchrotron science, medical imaging and astronomical telescopes such as the Square Kilometre Array, and related areas of science and engineering such as sports science, amusement parks, ballistics, forensics, black holes and dark matter.

Through the investigation of appropriate contexts, students explore the ways in which models and theories related to gravity and electromagnetism, and associated technologies, have developed over time and through interactions with social, economic, cultural and ethical considerations. They investigate the ways in which science contributes to contemporary debate about local, regional and international issues, including evaluation of risk and action for sustainability, and recognise the limitations of science to provide definitive answers in different contexts.

Students develop their understanding of field theories of gravity and electromagnetism through investigations of motion and electromagnetic phenomena. Through these investigations they develop skills in relating graphical representations of data to quantitative relationships between variables, using lines of force to represent vector fields, and interpreting interactions in two and three dimensions. They continue to develop skills in planning, conducting and interpreting the results of primary and secondary investigations and in evaluating the validity of primary and secondary data.

### Unit 3: Gravity and electromagnetism Learning Outcomes

By the end of this unit, students:

• understand that motion in gravitational, electric and magnetic fields can be explained using Newton’s Laws of Motion
• understand how the electromagnetic wave model explains the production and propagation of electromagnetic waves across the electromagnetic spectrum
• understand transformations and transfer of energy in electromagnetic devices, as well as transformations and transfer of energy associated with motion in electric, magnetic and gravitational fields
• understand how models and theories have developed over time, and the ways in which physical science knowledge and associated technologies interact with social, economic, cultural and ethical considerations
• use science inquiry skills to design, conduct, analyse and evaluate investigations into uniform circular motion, projectile motion, satellite motion and gravitational and electromagnetic phenomena, and to communicate methods and findings
• use algebraic and graphical representations to calculate, analyse and predict measurable quantities related to motion, gravitational effects and electromagnetic phenomena
• evaluate, with reference to evidence, claims about motion, gravity and electromagnetic phenomena and associated technologies, and justify evaluations
• communicate physics understanding using qualitative and quantitative representations in appropriate modes and genres.

### Unit 3: Gravity and electromagnetism Content Descriptions

#### Science Inquiry Skills

Identify, research and construct questions for investigation; propose hypotheses; and predict possible outcomes (ACSPH078)

Design investigations, including the procedure to be followed, the materials required, and the type and amount of primary and/or secondary data to be collected; conduct risk assessments; and consider research ethics (ACSPH079)

Conduct investigations, including the manipulation of force measurers and electromagnetic devices, safely, competently and methodically for the collection of valid and reliable data (ACSPH080)

Represent data in meaningful and useful ways, including using appropriate SI units, symbols and significant figures; organise and analyse data to identify trends, patterns and relationships; identify sources of uncertainty and techniques to minimise these uncertainties; utilise uncertainty and percentage uncertainty to determine the uncertainty in the result of calculations, and evaluate the impact of measurement uncertainty on experimental results; and select, synthesise and use evidence to make and justify conclusions (ACSPH081)

Interpret a range of scientific and media texts, and evaluate processes, claims and conclusions by considering the accuracy and precision of available evidence; and use reasoning to construct scientific arguments Interpret a range of scientific and media texts, and evaluate processes, claims and conclusions by considering the accuracy and precision of available evidence; and use reasoning to construct scientific arguments (ACSPH082)

Select, construct and use appropriate representations, including text and graphic representations of empirical and theoretical relationships, vector diagrams, free body/force diagrams, field diagrams and circuit diagrams, to communicate conceptual understanding, solve problems and make predictions (ACSPH083)

Select, use and interpret appropriate mathematical representations, including linear and non-linear graphs and algebraic relationships representing physical systems, to solve problems and make predictions (ACSPH084)

Communicate to specific audiences and for specific purposes using appropriate language, nomenclature, genres and modes, including scientific reports (ACSPH085)

#### Science as a Human Endeavour (Units 3 & 4)

ICT and other technologies have dramatically increased the size, accuracy and geographic and temporal scope of datasets with which scientists work (ACSPH086)

Models and theories are contested and refined or replaced when new evidence challenges them, or when a new model or theory has greater explanatory power (ACSPH087)

The acceptance of science understanding can be influenced by the social, economic and cultural context in which it is considered (ACSPH088)

People can use scientific knowledge to inform the monitoring, assessment and evaluation of risk (ACSPH089)

Science can be limited in its ability to provide definitive answers to public debate; there may be insufficient reliable data available, or interpretation of the data may be open to question (ACSPH090)

International collaboration is often required when investing in large-scale science projects or addressing issues for the Asia-Pacific region (ACSPH091)

Scientific knowledge can be used to develop and evaluate projected economic, social and environmental impacts and to design action for sustainability (ACSPH092)

#### Gravity and motion

Examples in context

Support materials only that illustrate some possible contexts for exploring Science as a Human Endeavour concepts in relation to Science Understanding content.

## Forensic science - projectiles

Ballistics is the study of the flight of projectiles, especially bullets. The path of a bullet can be predicted by understanding the effects of air resistance and gravity, and determining the effect of environmental conditions. Scientists study and record the motion of bullets through use of analytical methods such as high speed video analysis and 3D computer modelling (ACSPH086). Databases have been created recording the motion of a variety of bullets from different weapons and computer matching is used to identify weapons used in crimes (ACSPH086). Forensic evidence is often used in court though, despite messages in the popular media, forensic science cannot always provide sufficient conclusive evidence to lead to convictions (ACSPH090).

## Artificial satellites

Artificial satellites are used for communication, research and observation. Knowledge of orbital heights and speeds allow satellites to be best positioned for observation of weather, natural phenomena, traffic and military movements (ACSPH092). Communication via satellite is now used in GPS, satellite phones and television. Orbits and uses of satellites are classified by altitude (Low Earth, Medium Earth or High Earth) and by inclination (equatorial, polar, polar sun-synchronous). Thousands of decommissioned satellites, spent rocket stages and fragments from collisions (collectively called space debris) continue to orbit Earth, causing problems upon collision with functional satellites and posing danger upon re-entry into Earth’s atmosphere. Various strategies including active removal are in place to try to limit an increase in orbiting debris (ACSPH089).

## Developing understanding of planetary motion

Ptolemaic astronomy proposed a geocentric model of the solar system that used the idea of epicycles to explain planetary movement. This model was used until Copernicus proposed a heliocentric model of the solar system (ACSPH087) which was later championed by Galileo, causing conflict with the Catholic church (ACSPH088). Johannes Kepler proposed three laws of planetary motion which form the basis of our modern understanding of orbits. Newton was able to show how these laws were derived from his theory of gravitation (ACSPH087).

Mathematical representations and relationships

$$\mathrm w=\mathrm m\mathrm g$$

$$\mathrm w\;=\;$$ weight force, $$\mathrm m\;=\;$$ mass, $$\mathrm g\;=\;$$ acceleration due to gravity (gravitational field strength)

$$\mathrm F=\frac{\mathrm G\mathrm M\mathrm m}{\mathrm r^2}$$ and $$\mathrm g=\frac{\mathrm F}{\mathrm m}=\frac{\mathrm G\mathrm M}{\mathrm r^2}$$

$$\mathrm F\;=\;$$ gravitational force, $$\mathrm G\;=\;$$ G = universal constant of gravitation

$$\left(6.67\;\times\;10^{-11}\;\mathrm N\;\mathrm m^2\;\mathrm k\mathrm g^{-2}\right)$$, $$\mathrm M\;=\;$$ M = mass of first body, $$\mathrm m\;=\;$$ mass of second body, $$\;\mathrm r\;=\;$$ separation between the centres of mass of the two bodies, $$\mathrm g$$ = acceleration due to gravity

$${\mathrm v}_\mathrm y=\mathrm g\mathrm t+\;{\mathrm u}_\mathrm y$$, $$\mathrm y=\;½\;\mathrm g\mathrm t^2+\;{\mathrm u}_\mathrm y\mathrm t$$, $${\mathrm v}_\mathrm y^2=2\mathrm g\mathrm y+\;{\mathrm u}_\mathrm y^2$$, $${\mathrm v}_{\mathrm x\;}=\;{\mathrm u}_\mathrm x$$ and $$\mathrm x=\;{\mathrm u}_\mathrm x\mathrm t$$

$$\mathrm y\;=$$ vertical displacement, x = horizontal displacement, $${\mathrm u}_\mathrm y=\;$$ initial vertical velocity, $$\;{\mathrm v}_\mathrm y=\;$$ vertical velocity at time $$\mathrm t,\;$$, $${\mathrm u}_\mathrm x=$$ initial horizontal velocity, $${\mathrm v}_\mathrm x\;=$$ horizontal velocity at time $$\mathrm t,\;$$, $$\mathrm g\;=$$ speed of light acceleration due to gravity, $$\mathrm t,\;$$ time into flight

$$\mathrm v=\frac{2\mathrm\pi\mathrm r}{\mathrm T}$$

$$\mathrm v=\;$$ tangential velocity, $$\;\mathrm T$$ = period

$${\mathrm a}_\mathrm c=\frac{\mathrm v^2}{\mathrm r}$$

$${\mathrm a}_\mathrm c\;=$$ centripetal acceleration, $$\mathrm v\;=$$ tangential velocity, $$\mathrm r\;=$$ radius of the circle

$${\mathrm F}_{\mathrm n\mathrm e\mathrm t}=\;\frac{\mathrm m\mathrm v^2}{\mathrm r}$$

$${\mathrm F}_{\mathrm n\mathrm e\mathrm t}=\;$$ net force, $$\mathrm m\;=$$ mass of body undergoing uniform circular motion, $$\mathrm v=\;$$ v= tangential velocity, r = radius of the circle

$$\frac{\mathrm T^2}{\mathrm r^3}=\frac{4\mathrm\pi^2}{\mathrm G\mathrm M}$$

$$\mathrm T\;=$$ period of satellite, $$\mathrm M\;=$$ mass of the central body, $$\mathrm r\;=$$ orbital radius, $$\mathrm G\;=\;$$ universal constant of gravitation

$$\left(6.67\;\times\;10^{-11}\;\mathrm N\;\mathrm m^2\;\mathrm k\mathrm g^{-2}\right)$$

The movement of free-falling bodies in Earth’s gravitational field is predictable (ACSPH093)

All objects with mass attract one another with a gravitational force; the magnitude of this force can be calculated using Newton’s Law of Universal Gravitation (ACSPH094)

Objects with mass produce a gravitational field in the space that surrounds them; field theory attributes the gravitational force on an object to the presence of a gravitational field (ACSPH095)

When a mass moves or is moved from one point to another in a gravitational field and its potential energy changes, work is done on or by the field (ACSPH096)

Gravitational field strength is defined as the net force per unit mass at a particular point in the field (ACSPH097)

The vector nature of the gravitational force can be used to analyse motion on inclined planes by considering the components of the gravitational force (that is, weight) parallel and perpendicular to the plane (ACSPH098)

Projectile motion can be analysed quantitatively by treating the horizontal and vertical components of the motion independently (ACSPH099)

When an object experiences a net force of constant magnitude perpendicular to its velocity, it will undergo uniform circular motion, including circular motion on a horizontal plane and around a banked track (ACSPH100)

Newton’s Law of Universal Gravitation is used to explain Kepler’s laws of planetary motion and to describe the motion of planets and other satellites, modelled as uniform circular motion (ACSPH101)

#### Electromagnetism

Examples in context

Support materials only that illustrate some possible contexts for exploring Science as a Human Endeavour concepts in relation to Science Understanding content.

## Medical imaging

Magnetic Resonance Imaging (MRI) uses the property of nuclear magnetic resonance (NMR) to magnetise nuclei inside the body and create clear and accurate images of internal structures. MRI has many advantages over other imaging techniques such as computed tomography (CT) scans and X-rays, including greater contrast between soft tissues (ACSPH086) and an ability to take images without the use of ionising radiation (ACSPH089). Due to the strong magnetic fields used in these machines, there are many safety procedures that must be followed and the procedure is often unsuitable for people with metallic implants or possible allergies to the contrast agents used (ACSPH089).

## The Square Kilometre Array

The Square Kilometre Array (SKA) is a large radio telescope project jointly developed by a number of countries and organisations, which is to be built in multiple countries but primarily Australia, New Zealand and South Africa (ACSPH091). Current information indicates it will be tens of times more sensitive than any other radio instrument, with an ability to survey the sky thousands of times faster. One of the major challenges is the requirement for extremely high data transfer and computing power. Advances in this area will flow through to all areas of everyday computing (ACSPH086). Aims of the project include gathering information to advance our knowledge of dark matter and energy, cosmic magnetism and tests of general relativity, which would not be possible without the SKA (ACSPH086).

## Superconductivity

Superconductivity is the phenomena observed when certain materials are cooled below a characteristic temperature, and zero electrical resistance occurs. Superconductors also exhibit the Meissner effect, where all magnetic flux inside is cancelled. Superconductivity was discovered in 1911 when the resistance of mercury was found to drop to zero at very low temperatures. A series of discoveries caused a number of theories to be put forward to explain the phenomena, but it was not until the late 1950s that a complete atomic scale theory of superconductivity was proposed (ACSPH087). Since then, the development of high-temperature superconductors and practical applications for them have been the focus of research. Superconductors are used in magnetic levitation, such as in maglev trains, mass spectrometers, and in magnetic imaging (MRI). An extremely powerful and large superconducting magnet has been built for use inside the Large Hadron Collider at CERN (ACSPH092).

Mathematical representations and relationships

$$\mathrm F=\;\frac1{4\mathrm\pi{\mathrm\varepsilon}_0}\frac{\mathrm Q\mathrm q}{\mathrm r^2}$$

$$\mathrm F=$$ force, $$\frac1{4\mathrm\pi{\mathrm\varepsilon}_\mathrm o}=$$ Coulomb constant

$$\left(9\;\times\;10^9\;\mathrm N\;\mathrm m^2\;\mathrm C^{-2}\right)$$, $$\mathrm q\;=$$ charge on the first object, $$\mathrm Q\;=$$ charge on the second object, $$\mathrm r\;=$$ separation between the charges

$$\mathrm E=\frac{\mathrm F}{\mathrm q}=\frac1{4\mathrm\pi{\mathrm\varepsilon}_0}\frac{\mathrm q}{\mathrm r^2}$$

$$\mathrm E\;=$$ electric field strength, $$\mathrm F\;=\;$$ force, $$\mathrm q\;=$$ charge, $$\mathrm r\;=$$ distance from the charge, $$\;\frac1{4\mathrm\pi{\mathrm\varepsilon}_\mathrm o}=$$ Coulomb constant

$$\left(9\;\times\;10^9\;\mathrm N\;\mathrm m^2\;\mathrm C^{-2}\right)$$

$$\mathrm V=\frac{\mathrm\Delta\mathrm U}{\mathrm q}$$

$$\mathrm V\;=$$ electrical potential difference, $$\mathrm\Delta\mathrm U\;=$$ change in potential energy, $$\mathrm q\;=$$ charge

$$\mathrm B=\frac{µ_\mathrm o\mathrm I}{2\mathrm\pi\mathrm r}$$

$$\mathrm B\;=$$ magnetic flux density, $$\mathrm I\;=$$ current in wire, $$\mathrm r\;=$$ distance from the centre of the wire, $$\;\frac{µ_\mathrm o}{2\mathrm\pi}=$$ magnetic constant

$$\text{(2 × }10^{-7}\text{T }\text{A}^{-1}\text{m)}$$

For a straight, current carrying wire perpendicular to a magnetic field $$\mathrm F=\mathrm B\mathrm I\mathrm l$$

$$\mathrm B\;=$$ magnetic flux density, $$\mathrm F=$$ force on the wire, $$\mathrm l=$$ l=length of wire in the magnetic field, $$\mathrm I$$ = current in the wire

For a charge moving perpendicular to a magnetic field $$\mathrm F=\mathrm q\mathrm v\mathrm B$$

$$\mathrm F=$$ force on a charge moving in an applied magnetic field, $$\mathrm q\;=$$ charge, $$\mathrm v=\;$$ velocity of the charge, $$\mathrm B\;=$$ magnetic flux density

$$\mathrm\phi=\mathrm B{\mathrm A}_\perp$$

$$\mathrm\phi=\;$$ magnetic flux, $${\mathrm A}_\perp=\;$$ area of current loop perpendicular to the applied magnetic field, $$\mathrm B\;=$$ magnetic flux density

$$\mathrm e\mathrm m\mathrm f=-\;\frac{\mathrm n\bigtriangleup(\mathrm B{\mathrm A}_\perp)}{\operatorname\Delta\mathrm t}=-\;\mathrm n\frac{\operatorname\Delta\mathrm\phi}{\operatorname\Delta\mathrm t}$$

$$\mathrm e\mathrm m\mathrm f=$$ induced potential difference, $$\triangle\mathrm\phi\;=$$ change in magnetic flux, $$\mathrm n\;=$$ number of windings in the loop, $${\mathrm A}_\perp=\;$$ area of current loop perpendicular to the applied magnetic field, $$\operatorname\Delta\mathrm t\;=$$ time interval over which the magnetic flux change occurs, $$\mathrm B\;=$$ magnetic flux density

$$\frac{{\mathrm V}_\mathrm p}{{\mathrm V}_\mathrm s}=\frac{{\mathrm n}_\mathrm p}{{\mathrm n}_\mathrm s}$$

$${\mathrm V}_\mathrm p=$$ potential difference across the primary coil, $$\;{\mathrm V}_\mathrm s=\;$$ Vs= potential difference across the secondary coil, $${\mathrm n}_\mathrm p\;=$$ number of turns on primary coil, $${\mathrm n}_\mathrm s=$$ number of turns on secondary coil

$${\mathrm I}_\mathrm p{\mathrm V}_\mathrm p={\mathrm I}_\mathrm s{\mathrm V}_\mathrm s\;$$

$${\mathrm I}_\mathrm p=$$ current in primary coil, $${\mathrm V}_\mathrm p=\;$$ Vp= potential difference across primary coil, $${\mathrm I}_\mathrm s$$ = current in secondary coil, $$\;{\mathrm V}_\mathrm s$$ = potential difference across secondary coil

Electrostatically charged objects exert a force upon one another; the magnitude of this force can be calculated using Coulomb’s Law (ACSPH102)

Point charges and charged objects produce an electric field in the space that surrounds them; field theory attributes the electrostatic force on a point charge or charged body to the presence of an electric field (ACSPH103)

A positively charged body placed in an electric field will experience a force in the direction of the field; the strength of the electric field is defined as the force per unit charge (ACSPH104)

When a charged body moves or is moved from one point to another in an electric field and its potential energy changes, work is done on or by the field (ACSPH105)

Current-carrying wires are surrounded by magnetic fields; these fields are utilised in solenoids and electromagnets (ACSPH106)

The strength of the magnetic field produced by a current is called the magnetic flux density (ACSPH107)

Magnets, magnetic materials, moving charges and current-carrying wires experience a force in a magnetic field; this force is utilised in DC electric motors (ACSPH108)

Magnetic flux is defined in terms of magnetic flux density and area (ACSPH109)

A changing magnetic flux induces a potential difference; this process of electromagnetic induction is used in step-up and step-down transformers, DC and AC generators, and AC induction motors (ACSPH110)

Conservation of energy, expressed as Lenz’s Law of electromagnetic induction, is used to determine the direction of induced current (ACSPH111)

Electromagnetic waves are transverse waves made up of mutually perpendicular, oscillating electric and magnetic fields (ACSPH112)

Oscillating charges produce electromagnetic waves of the same frequency as the oscillation; electromagnetic waves cause charges to oscillate at the frequency of the wave (ACSPH113)