Physics Unit 3
Unit 3: Gravity and Electromagnetism
In Unit 3, students develop a deeper understanding of motion and its causes by Use Newton’s laws of motion and the gravitational field model to analyse motion on inclined planes, and the motion of projectiles and satellites. 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. Students develop their understanding of field theories of gravity and electromagnetism through investigations of motion and electromagnetic phenomena. Finally, they will 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.
Participation in a range of experiments and investigations will allow students to 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.
Throughout the unit, students develop skills in planning and conducting investigations, interpreting results and evaluating the validity of primary and secondary data, as well as the communication of these evaluations to others in a range of formats.
Unit Objectives
| 1. | Describe ideas and findings about gravity and motion, and electromagnetism. |
| 2. | Apply understanding of gravity and motion, and electromagnetism. |
| 3. | Analyse data about gravity and motion, and electromagnetism. |
| 4. | Interpret evidence about gravity and motion, and electromagnetism. |
| 5. | Evaluate processes, claims and conclusions about gravity and motion, and electromagnetism. |
| 6. | Investigate phenomena associated with gravity and motion, and electromagnetism. |
Subject Matter
Topic 1: Gravity and Motion (22 hours)
Science Understanding
The following subject matter can be assessed in the external assessment.
Projectile Motion
- Apply vector analysis to resolve a vector into two perpendicular components.
- Solve vector problems by resolving vectors into components, adding or subtracting the components and recombining them to Determine the resultant vector.
- Describe how horizontal and vertical components of a velocity vector are independent of each other.
- Solve problems involving projectile motion in the absence of drag effects using vy= uy+gt, sy= uyt+ 12gt2, v2y=u2y+ 2gsy, vx=ux and sx=uxt.
- Interpret data relating to the horizontal distance travelled by an object projected at various angles from the horizontal.
Inclined Planes and Circular Motion
- Solve problems involving force due to gravity (weight) and mass using Fg=mg.
- Describe the concept of normal force.
- Describe the forces acting on an object on an inclined plane (e.g. force due to gravity, normal force, tension, frictional force and applied force) through the Use of free-body diagrams.
- Determine the net force acting on an object on an inclined plane using vector analysis.
- Describe the concept of uniform circular motion.
- Describe the concepts of average speed and period.
- Solve problems involving objects undergoing uniform circular motion at a constant speed using v=2πrT and ac=v2r.
- Describe the concepts of centripetal acceleration and centripetal force.
- Solve problems involving forces acting on objects in uniform circular motion using Fc=Fnet=mv2r.
Orbital Mechanics
- Describe the Law of Universal Gravitation.
- Solve problems involving the magnitude of the gravitational force between two masses using F=GMmr2 .
- Describe the concept of gravitational fields.
- Solve problems involving the gravitational field strength at a distance from an object using g=Fm=GMr2.
- State the three laws of planetary motion.
- Describe the relationship between the Law of Universal Gravitation and uniform circular motion and Recognise this as the third law of planetary motion.
- Solve problems involving the third law of planetary motion using Ta2ra3=Tb2rb3=4π2GM.
Science as a Human Endeavour (SHE)
The following subject matter may be assessed in the internal assessments.
- Appreciate the significant contributions of scientists such as Isaac Newton, Johannes Kepler, Émilie du Châtelet and Katherine Johnson who furthered our understanding of gravity and motion.
- Explore the role of forensic evidence used in court and the challenges associated with providing conclusive evidence that may lead to convictions.
- Appreciate how the accepted model of the solar system slowly shifted under the influence of carefully collected and analysed data.
- Explore the difficulties experienced by scientists who supported a heliocentric model of the solar system and the hindrances to the acceptance of their discoveries by society.
- Consider the international collaboration required to monitor the orbits of satellites, and the management of space debris.
- Consider the factors that contribute to positioning of satellites used for observation of weather, natural phenomena, traffic and military movements.
- Explore the international collaboration required in the discovery of gravity waves and associated technologies, e.g. Laser Interferometer Gravitational Wave Observatory (LIGO).
Science Inquiry
The following subject matter may be assessed in the internal assessments.
- Consider how an object can travel at a constant speed yet be accelerating.
- Investigate the horizontal distance travelled by an object projected at various angles from the horizontal.
- Investigate the parallel component of the weight of an object down an inclined plane at various angles.
- Investigate the net forces acting on an object undergoing horizontal circular motion on a string.
- Consider the difference between the heliocentric and geocentric models of the solar system.
- Investigate the relationship between orbital radius and mass for orbiting objects using a simulation.
Topic 2: Electromagnetism (23 hours)
Science Understanding
The following subject matter can be assessed in the external assessment.
Electrostatics
- Describe Coulomb’s Law.
- Solve problems using F= 14πεoQqr2=kQqr2.
- Describe the concepts of electric fields, electric field strength and electrical potential energy.
- Solve problems involving electric field strength using E= FQ=14πεoqr2=kqr2.
- Solve problems involving the work done when an electric charge is moved in an electric field using V= ΔUq.
Magnetic Fields
- Describe the concept of a magnetic field.
- Draw magnetic field lines due to a moving electric charge, electric currents and magnets.
- Describe the generation of a magnetic field from a moving electric charge.
- Solve problems involving the magnitude and direction of magnetic fields around a straight electric current-carrying wire and inside a solenoid using B= μoI2πr and B= μonI.
- Describe the force experienced by electric current-carrying conductors and moving electric charges when placed in a magnetic field.
- Solve problems involving the magnetic force on an electric current-carrying wire and moving charge in a magnetic field using F=BILsinθ and F=qvBsinθ.
- Interpret data relating to the force acting on a conductor in a magnetic field.
- Interpret data relating to the strength of a magnet at various distances.
Electromagnetic Induction
- Describe the concepts of magnetic flux, magnetic flux density, electromagnetic induction, electromotive force (EMF), Faraday’s Law and Lenz’s Law.
- Solve problems involving the magnetic flux in an electric current-carrying loop using ∅=BAcosθ.
- Describe the process of inducing an EMF across a moving conductor in a magnetic field.
- Explain how Lenz’s Law is consistent with the principle of conservation of energy.
- Explain how transformers work in terms of Faraday’s Law and electromagnetic induction.
- Solve problems involving electromagnetic induction using emf=−NΔ(BA⊥)Δt, emf=−NΔϕΔt, IpVp= IsVs and VpVs=NpNs.
- Describe the concept of an electromagnetic wave.
- Explain the relationship between oscillating electric charges and electromagnetic waves.
Science as a Human Endeavour (SHE)
The following subject matter may be assessed in the internal assessments.
- Appreciate the significant contributions of scientists such as Charles-Augustin de Coulomb, Michael Faraday, Emil Lenz, Mary Somerville and James Clerk Maxwell who furthered our understanding of electromagnetism.
- Explore how scientific knowledge has allowed the development of new methods for renewable energy production.
- Consider the scientific evidence concerning the risks of electromagnetic phenomena and associated technologies (e.g. wi-fi and mobile phones) as reported in the media.
- Explore the international collaboration involved in the development of the Square Kilometre Array (SKA) and the associated technologies to gather information that advances our knowledge of dark matter, dark energy, cosmic magnetism and general relativity.
- Consider the safety procedures developed for instruments that rely on strong magnetic fields (e.g. MRI and NMR machines).
- Explore the discoveries and theories that led to our current understanding of superconductivity.
Science Inquiry
The following subject matter may be assessed in the internal assessments.
- Investigate the force acting on a conductor in a magnetic field.
- Investigate the strength of a magnet at various distances.
- Investigate the effects of electrostatic charge on various materials, e.g. on trickling water.
- Consider how electricity is made.
- Investigate the induction of an electric current using a magnet and coil.
- Investigate the induced EMF from an AC generator.
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