Physics Unit 2
Unit 2: Linear Motion and Waves
In Unit 2, 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 displacement, velocity, acceleration and time data, and examine the relationships between force, momentum and energy for interactions in one dimension. Students also investigate common wave phenomena, Use waves on springs, sound waves and consideration of seismic waves. They compare the behaviour of these waves with the behaviour of light, leading to an explanation of light phenomena, including constructive and destructive 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, 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).
Participation in a range of experiments and investigations will allow students to progressively develop their suite of science inquiry skills, while gaining an enhanced appreciation of the range of technologies that have contributed to the development of physics understanding. Collaborative experimental work also helps students to develop communication, interaction, character and management skills.
Throughout the unit, students also 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 continue to develop skills in planning and conducting investigations and interpreting the results.
Unit Objectives
| 1. | Describe ideas and findings about linear motion and force, and waves. |
| 2. | Apply understanding of linear motion and force, and waves. |
| 3. | Analyse data about linear motion and force, and waves. |
| 4. | Interpret evidence about linear motion and force, and waves. |
| 5. | Evaluate processes, claims and conclusions about linear motion and force, and waves. |
| 6. | Investigate phenomena associated with linear motion and force, and waves. |
Subject Matter
Topic 1: Linear Motion and Force (25 hours)
Science Understanding
Linear Motion
- Contrast vectors and scalars, and Use these terms to categorise physical quantities, e.g. velocity and speed.
- Symbolise vectors graphically and algebraically, e.g. F, ˜F and →F.
- Calculate resultant vectors through the addition and subtraction of two vectors in one dimension.
- Describe the concepts of displacement, velocity and acceleration.
- Compare instantaneous and average velocity.
- Interpret linear motion graphs to describe the motion of an object, referring to the
- intercepts, gradients and uncertainties (using minimum and maximum lines of best fit) of displacement–time and velocity–time graphs
- areas under velocity–time and acceleration–time graphs using simple geometry.
- Solve problems relating to uniformly accelerated motion in one dimension using
, and . - Interpret experimental data to Determine the value of acceleration due to gravity on the Earth’s surface.
Classical Mechanics
- Describe the three laws of motion of classical mechanics and give examples of each.
- Identify forces acting on an object.
- Draw free-body diagrams representing forces such as the force due to gravity (weight), the normal force, tension, friction, drag and applied forces acting on an object.
- Determine the resultant force acting on an object in one dimension.
- Solve problems using the laws of classical mechanics and a=Fnetm.
- Describe the concepts of momentum and impulse.
- Describe the principle of conservation of momentum.
- Solve problems involving momentum, impulse, the conservation of momentum and collisions in one dimension using p=mv and ∑mvbefore= ∑mvafter.
- Analyse the area under a force–time Draw using geometric methods.
Energy
- Describe the concepts of mechanical work, kinetic energy and gravitational potential energy.
- Solve problems involving work done by a force using W= ΔE and W=Fs.
- Solve problems involving kinetic energy and gravitational potential energy using Ek= 12mv2 and ΔEp=mgΔh.
- Analyse the area under a force–displacement graph using geometric methods.
- Interpret energy–time graphs.
- Discuss the differences between elastic and inelastic collisions.
- Solve problems involving elastic collisions and inelastic collisions (including explosions) using ∑12mv2before= ∑12mv2after.
Science as a Human Endeavour (SHE)
- Appreciate the significant contributions of scientists such as Isaac Newton and Émilie du Châtelet.
- Explore historical models and theories used to describe motion and force, and how evidence was used to build upon and improve on earlier understandings.
- Consider how knowledge of forces and motion has led to improvements in car safety through the development of technologies such as seatbelts, crumple zones and airbags.
- Understand the study of biomechanics applies the laws of forces and motion, and through direct measurement, computer simulation and mathematical modelling lead to a better understanding of human movement and improved athletic performance.
- Appreciate that the laws of motion proposed by Isaac Newton provided an explanation for a range of previously unexplained physical phenomena, which were confirmed by multiple experiments performed by a multitude of scientists.
Science Inquiry
- Explore the variations in final position of a person who walks 100 m.
- Consider the fable of the tortoise and the hare, and how the slow-moving tortoise was able to beat the faster hare.
- Explore the role physics plays in improving the performance of elite athletes.
- Investigate situations that involve displacement–time and velocity–time graphs.
- Use vertical error bars when plotting data to determine the uncertainty of the gradient and intercepts using minimum and maximum lines of best fit.
- Investigate a linear elastic collision between two objects.
- Linearise a dataset that suggests a non-linear relationship (e.g. t__2 versus s) and calculate the equation of the linear trend line.
Topic 2: Waves (20 hours)
Science Understanding
Wave Properties
- Describe the transfer of energy through waves.
- Describe the concept of mechanical waves.
- Compare transverse waves and longitudinal waves.
- Describe examples of transverse and longitudinal waves, such as sound, seismic waves and vibrations of stringed instruments.
- Describe the concepts of compression, rarefaction, crest, trough, displacement, amplitude, period, frequency, wavelength and velocity and identify them on graphical and visual representations of a wave.
- Analyse the amplitude, period, frequency and wavelength from graphs of transverse and longitudinal waves.
- Solve problems involving the period, frequency, wavelength, and velocity of a wave using v=fλ and f=1T and using but not limited to vs=346 m s−1.
- Describe the concepts of reflection, refraction, diffraction and superposition.
- Explain phenomena related to reflection and refraction using the wave model of light.
- Describe the reflection and refraction of a wave at a boundary between two media.
- Explain constructive interference and destructive interference of two simple waves.
- Determine the resultant amplitude of two simple waves interacting using the principle of superposition.
- Explain the formation of standing waves in terms of superposition with reference to constructive and destructive interference, and nodes and antinodes.
Sound
- Describe the concepts of fundamental (or first) harmonic and natural frequency.
- Solve problems involving standing wave formation in pipes open at both ends, closed at one end, and on stretched strings using L=nλ2 and L=(2n−1)λ4.
- Describe the concept of resonance in a mechanical system.
- Identify that energy is transferred efficiently in resonating systems.
Light
- Compare light to a mechanical wave.
- Explain the concepts of reflection, refraction, total internal reflection, dispersion, diffraction and interference in relation to the wave model of light.
- Describe polarisation using a transverse wave model.
- Construct ray diagrams to demonstrate the reflection and refraction of light.
- Solve problems involving the reflection of light on single plane mirrors and refraction of light through a single convex or concave lens using ray diagrams to identify the location, orientation and size of an image.
- Describe the concept of Snell’s Law.
- Solve problems involving the refraction of light at the boundary between two mediums using sinisinr= v1v2= λ1λ2=n2n1.
- Contrast the speed of light and the speed of mechanical waves.
- Describe the concept of intensity and its proportionality to the square of the amplitude.
- Solve problems involving the proportional relationship between intensity of light and the inverse-square of the distance from the source using I∝1r2.
- Determine the refractive index of a transparent substance from experimental data.
Science as a Human Endeavour (SHE)
- Appreciate the significant contributions of scientists such as Laura Bassi, Willebrord Snellius, Albert A Michelson and Edward W Morley.
- Appreciate the role of experiments in furthering our understanding of light and its wave-like behaviour.
- Consider the importance of wave properties in experiments such as those performed by Michelson and Morley to demonstrate light waves travel through a vacuum and not the luminiferous aether as was believed at the time.
- Appreciate that 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.
- Consider how acoustical engineering can reduce noise pollution by planning structures that absorb sound waves or that do not reflect and amplify sound in an unwanted way.
Science Inquiry
- Consider the apparent position of objects under water in relation to observations made through different media.
- Investigate the behaviour of both longitudinal waves and transverse waves on springs in relation to reflection from fixed and free ends and transmission/reflection at a medium boundary.
- Investigate fundamental and harmonic wavelengths in pipes.
- Investigate the speed of sound in air at a specific temperature.
- Investigate the law of reflection.
- Investigate the refractive properties of different substances.
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