# 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 2: Linear Motion and Waves

### Unit 2: Linear Motion and Waves Description

In this unit, students develop an appreciation of how an understanding of motion and waves can be used to describe, explain and predict a wide range of phenomena. Students describe linear motion in terms of position and time data, and examine the relationships between force, momentum and energy for interactions in one dimension.

Students investigate common wave phenomena, including waves on springs, and water, sound and earthquake waves, and compare the behaviour of these waves with the behaviour of light. This leads to an explanation of light phenomena, including polarisation, interference and diffraction, in terms of a wave model.

Contexts that could be investigated in this unit include technologies such as accelerometers, motion-detectors, photo radar, GPS, energy conversion buoys, music, hearing aids, echo locators, fibre optics, DVDs and lasers, and related areas of science and engineering such as sports science, car and road safety, acoustic design, noise pollution, seismology, bridge and building design.

Through the investigation of appropriate contexts, students explore how international collaboration, evidence from a range of disciplines and many individuals, and the development of ICT and other technologies have contributed to developing understanding of motion and waves and associated technologies. They investigate how scientific knowledge is used to offer valid explanations and reliable predictions, and the ways in which it interacts with social, economic, cultural and ethical factors.

Students develop their understanding of motion and wave phenomena through laboratory investigations. They develop skills in relating graphical representations of data to quantitative relationships between variables, and they continue to develop skills in planning, conducting and interpreting the results of primary and secondary investigations.

### Unit 2: Linear Motion and Waves Learning Outcomes

By the end of this unit, students:

• understand that Newton’s Laws of Motion describe the relationship between the forces acting on an object and its motion
• understand that waves transfer energy and that a wave model can be used to explain the behaviour of sound and light
• understand how scientific models and theories have developed and are applied to improve existing, and develop new, technologies
• use science inquiry skills to design, conduct and analyse safe and effective investigations into linear motion and wave phenomena, and to communicate methods and findings
• use algebraic and graphical representations to calculate, analyse and predict measurable quantities associated with linear and wave motion
• evaluate, with reference to evidence, claims about motion, sound and light-related phenomena and associated technologies
• communicate physics understanding using qualitative and quantitative representations in appropriate modes and genres.

### Unit 2: Linear Motion and Waves Content Descriptions

#### Science Inquiry Skills

Identify, research and construct questions for investigation; propose hypotheses; and predict possible outcomes (ACSPH045)

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 (ACSPH046)

Conduct investigations, including the manipulation of devices to measure motion and the direction of light rays, safely, competently and methodically for the collection of valid and reliable data (ACSPH047)

Represent data in meaningful and useful ways, including using appropriate SI units and symbols; organise and analyse data to identify trends, patterns and relationships; identify sources of random and systematic error and estimate their effect on measurement results; identify anomalous data and calculate the measurement discrepancy between the experimental results and a currently accepted value, expressed as a percentage; and select, synthesise and use evidence to make and justify conclusions (ACSPH048)

Interpret a range of scientific and media texts, and evaluate processes, claims and conclusions by considering the quality of available evidence; and use reasoning to construct scientific arguments (ACSPH049)

Select, construct and use appropriate representations, including text and graphic representations of empirical and theoretical relationships, vector diagrams, free body/force diagrams, wave diagrams and ray diagrams, to communicate conceptual understanding, solve problems and make predictions (ACSPH050)

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 (ACSPH051)

Communicate to specific audiences and for specific purposes using appropriate language, nomenclature, genres and modes, including scientific reports (ACSPH052)

#### Science as a Human Endeavour (Units 1 & 2)

Science is a global enterprise that relies on clear communication, international conventions, peer review and reproducibility (ACSPH053)

Development of complex models and/or theories often requires a wide range of evidence from multiple individuals and across disciplines (ACSPH054)

Advances in science understanding in one field can influence other areas of science, technology and engineering (ACSPH055)

The use of scientific knowledge is influenced by social, economic, cultural and ethical considerations (ACSPH056)

The use of scientific knowledge may have beneficial and/or harmful and/or unintended consequences (ACSPH057)

Scientific knowledge can enable scientists to offer valid explanations and make reliable predictions (ACSPH058)

Scientific knowledge can be used to develop and evaluate projected economic, social and environmental impacts and to design action for sustainability (ACSPH059)

#### Linear motion and force

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.

Knowledge of forces and motion has led to developments that have reduced the risks for drivers, their passengers, and other road users such as cyclists and pedestrians. Car safety has improved through the development and use of devices such as seatbelts, crumple zones and airbags. An understanding of motion has also led to the design and implementation of traffic-calming devices such as speed bumps and safety barriers (ACSPH056). Knowledge of force and linear motion is used in forensic investigations into car accidents. Road laws and regulations, including the setting of speed limits in particular locations, are based on these scientific investigations and have resulted in lower road accident injuries and fatalities (ACSPH057).

## Sports science

The study of linear motion and forces has led to major developments in athlete training programs, sporting techniques and equipment development. Biomechanics applies the laws of force and motion to gain greater understanding of athletic performance through direct measurement, computer simulations and mathematical modelling (ACSPH054). Equipment such as bicycle frames and running shoes has been improved to reduce stresses and strains on athletes’ bodies. Many sports teams employ biomechanics experts to improve kicking, throwing or other techniques using knowledge of forces and motion. Advances in interpretation of video technologies, data logging and electronic detection and timing systems has also significantly improved reliability of judgements in sporting events (ACSPH055).

## Development and limitations of Newton’s Laws

Isaac Newton’s interest in how objects fall and the orbits of planets led to the writing and publication of Principia Mathematica, which outlined the Laws of Motion. Newton’s laws provided an explanation for a range of previously unexplained physical phenomena and were confirmed by multiple experiments performed by a multitude of scientists (ACSPH053). Newton’s laws of motion enable scientists to make reliable predictions, except when considering objects travelling at or near the speed of light, or very small objects like atoms or subatomic particles, or when very strong gravitational fields are involved (ACSPH058). Phenomena related to semiconductors, superconductors and errors in GPS systems cannot be predicted using Newton’s Laws and other theories must be used (ACSPH058).

Mathematical representations and relationships

$$\mathrm v=\mathrm u+\mathrm a\mathrm t,\;$$ $$\mathrm s=\mathrm u\mathrm t+\frac12\mathrm a\mathrm t^2,$$ $$\mathrm v^2=\mathrm u^2+2\mathrm a\mathrm s$$

$$\mathrm s=\;$$ displacement, $$\mathrm t$$ = time interval, $$\mathrm u=$$ initial velocity, $$\mathrm v=\;$$ final velocity, $$\mathrm a=\;$$ acceleration

$$\mathrm a=\frac{\mathrm F}{\mathrm m}$$

$$\mathrm a=\;$$ a= acceleration, $$\mathrm F=$$ force, $$\mathrm m\;=$$ mass

$$\mathrm W=\operatorname\Delta\mathrm E;\;$$ where the applied force is in the same direction as the displacement, $$\mathrm W=\mathrm F\mathrm s,\;$$

$$\mathrm W$$ = work, $$\;\mathrm F=\;$$ force, $$\;\mathrm s=$$ displacement, $$\operatorname\Delta\mathrm E=\;$$ change in energy

$$\mathrm p=\mathrm m\mathrm v,\;\;\mathrm\Delta\mathrm p=\mathrm F\mathrm\Delta\mathrm t$$

$$\mathrm p$$ = momentum, $$\mathrm v=\;$$ velocity, $$\mathrm m\;=$$ mass, $$\mathrm F\;$$ = force, $$\triangle\mathrm p=$$ change in momentum, $$\mathrm\Delta\mathrm t$$ = time interval over which force $$\mathrm F$$ acts

$${\mathrm E}_\mathrm k=\;\frac12\;\mathrm m\mathrm v^2$$

$${\mathrm E}_\mathrm k=$$ kinetic energy, $$\;\mathrm m=$$ mass, $$\mathrm v=\;$$ speed

$$\operatorname\Delta{\mathrm E}_\mathrm p=\mathrm m\mathrm g\operatorname\Delta\mathrm h$$

$$\operatorname\Delta{\mathrm E}_\mathrm p=\;$$ change in potential energy, $$\mathrm m=\;$$ mass, $$\mathrm g\;=\;$$ g = acceleration due to gravity, $$\triangle\mathrm h=$$ change in vertical distance

$$\mathrm\Sigma\mathrm m{\mathrm v}_{\mathrm b\mathrm e\mathrm f\mathrm o\mathrm r\mathrm e}=\;\mathrm\Sigma\mathrm m{\mathrm v}_{\mathrm a\mathrm f\mathrm t\mathrm e\mathrm r}$$

$$\mathrm\Sigma\mathrm m{\mathrm v}_{\mathrm b\mathrm e\mathrm f\mathrm o\mathrm r\mathrm e}=\;$$ vector sum of the momenta of all particles before the collision, $$\mathrm\Sigma\mathrm m{\mathrm v}_{\mathrm a\mathrm f\mathrm t\mathrm e\mathrm r}=$$ vector sum of the momenta of all particles after the collision

For elastic collisions:

$$\mathrm\Sigma\frac12\mathrm m\mathrm v_{\mathrm b\mathrm e\mathrm f\mathrm o\mathrm r\mathrm e}^2=\;\mathrm\Sigma\frac12\mathrm m\mathrm v_{\mathrm a\mathrm f\mathrm t\mathrm e\mathrm r}^2$$

$$\mathrm\Sigma\frac12\mathrm m\mathrm v_{\mathrm b\mathrm e\mathrm f\mathrm o\mathrm r\mathrm e}^2=$$ sum of the kinetic energies before the collision, $$\mathrm\Sigma\frac12\mathrm m\mathrm v_{\mathrm a\mathrm f\mathrm t\mathrm e\mathrm r}^2=$$ sum of the kinetic energies after the collision

Uniformly accelerated motion is described in terms of relationships between measurable scalar and vector quantities, including displacement, speed, velocity and acceleration (ACSPH060)

Representations, including graphs and vectors, and/or equations of motion, can be used qualitatively and quantitatively to describe and predict linear motion (ACSPH061)

Vertical motion is analysed by assuming the acceleration due to gravity is constant near Earth’s surface (ACSPH062)

Newton’s Three Laws of Motion describe the relationship between the force or forces acting on an object, modelled as a point mass, and the motion of the object due to the application of the force or forces (ACSPH063)

Momentum is a property of moving objects; it is conserved in a closed system and may be transferred from one object to another when a force acts over a time interval (ACSPH064)

Energy is conserved in isolated systems and is transferred from one object to another when a force is applied over a distance; this causes work to be done and changes to kinetic and/or potential energy of objects (ACSPH065)

Collisions may be elastic and inelastic; kinetic energy is conserved in elastic collisions (ACSPH066)

#### Waves

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.

## Monitoring earthquakes and tsunamis

Major catastrophes like the Japanese and Indian Ocean tsunamis and the Christchurch earthquakes have led to an increased need to monitor and record the plate movements that cause these phenomena. Various devices including seismographs and computer modelling are used to detect, determine the location of and predict effects of earthquakes and tsunamis (ACSPH058). Knowledge of different types of waves and their motion through the ocean and the continents allows prediction of the possible extent of damage or the timing of a tsunami. Earthquake engineering aims to limit seismic risk through design and construction of structures that are better able to resist the effects of earthquakes. A variety of methods including damping and suspension have been developed to protect buildings (ACSPH055).

## Noise pollution and acoustic design

Noise pollution comes from a variety of sources and is often amplified by walls, buildings and other built structures. Acoustical engineering, based on an understanding of the behaviour of sound waves, is used to reduce noise pollution. It focuses on absorbing sound waves or planning structures so that reflection and amplification does not occur (ACSPH058). When new roads are built, consideration is given to noise barrier design, surface materials and speed control. Buildings can be designed to limit the noise that enters from outside sources like roadways and low flying aircraft. Noise mitigation is also achieved by using particular materials for insulation and designing both the interior and exterior to reflect sound in particular ways. Safety equipment such as ear protection is compulsory and extensively tested for use in industrial situations due to the possible health consequences of exposure to excessive noise (ACSPH059).

## Development of the wave theory of light

In the late 17th century, Robert Hooke and Christiaan Huygens published early theories of light as a wave (ACSPH053) and around 1800 Thomas Young showed through experimentation that light passing through a double slit showed interference and thus wave properties. Young also developed principles of coherence and superposition of light. For many years, the presence of the luminiferous aether was proposed as the medium by which light is propagated, an idea that was later disproved by experiments such as the Michelson-Morley experiment (ACSPH054). Later, in the 1860s, James Clerk Maxwell developed a theory of electromagnetism and showed that electromagnetic waves would travel through space at the speed of light, implying light was an electromagnetic wave (ACSPH054).

Mathematical representations and relationships

$$\mathrm v=\mathrm f\mathrm\lambda$$

$$\mathrm v=$$ speed, $$\mathrm f=$$ frequency, $$\mathrm\lambda=$$ wavelength

angle of incidence = angle of reflection

$$\mathrm l=\;\mathrm n\frac{\mathrm\lambda}2$$ for strings attached at both ends and for pipes open at both ends

$$\mathrm l=\left(2\mathrm n-1\right)\frac{\mathrm\lambda}4\;$$ for pipes closed at one end

$$\mathrm n=$$ whole numbers 1, 2, 3… relating to the harmonic, $$\mathrm l=$$ length of string or pipe, $$\mathrm\lambda=\;$$ wavelength of sound wave

$$\mathrm I\propto\frac1{\mathrm r^2}\;$$

$$\;\mathrm I=$$ intensity, $$\mathrm r=$$ distance from the source

$$\frac{\sin\mathcal i}{\sin\mathrm r}=\;\frac{{\mathrm v}_1}{{\mathrm v}_2}=\frac{{\mathrm\lambda}_1}{{\mathrm\lambda}_2}$$

$$\mathrm i\;=\;$$ i = incident angle (relative to the normal), $$\mathrm r\;=\;$$ r = angle of refraction (relative to the normal), $${\mathrm v}_1=$$ velocity in medium 1, $$\;{\mathrm v}_2=$$ velocity in medium 2, $${\mathrm\lambda}_1=\;$$ wavelength in medium 1, $${\mathrm\lambda}_{2\;}$$ = wavelength in medium 2

Waves are periodic oscillations that transfer energy from one point to another (ACSPH067)

Longitudinal and transverse waves are distinguished by the relationship between the direction of oscillation relative to the direction of the wave velocity (ACSPH068)

Waves may be represented by time and displacement wave diagrams and described in terms of relationships between measurable quantities, including period, amplitude, wavelength, frequency and velocity (ACSPH069)

Mechanical waves transfer energy through a medium; mechanical waves may oscillate the medium or oscillate the pressure within the medium (ACSPH070)

The mechanical wave model can be used to explain phenomena related to reflection and refraction (for example, echoes, seismic phenomena) (ACSPH071)

The superposition of waves in a medium may lead to the formation of standing waves and interference phenomena, including standing waves in pipes and on stretched strings (ACSPH072)

A mechanical system resonates when it is driven at one of its natural frequencies of oscillation; energy is transferred efficiently into systems under these conditions (ACSPH073)

Light exhibits many wave properties; however, it cannot be modelled as a mechanical wave because it can travel through a vacuum (ACSPH074)

A ray model of light may be used to describe reflection, refraction and image formation from lenses and mirrors (ACSPH075)

A wave model explains a wide range of light-related phenomena including reflection, refraction, total internal reflection, dispersion, diffraction and interference; a transverse wave model is required to explain polarisation (ACSPH076)

The speed of light is finite and many orders of magnitude greater than the speed of mechanical waves (for example, sound and water waves); its intensity decreases in an inverse square relationship with distance from a point source (ACSPH077)