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SPH3U Physics Exam

SPH3U Physics Exam. Enduring Expectations Key Understandings. Waves. Two types of waves: linear and longitudinal Properties of all waves Universal wave equation: v=f l resonance. Waves can be classified as linear or longitudinal. Wave Properties. 5 major wave properties exist

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SPH3U Physics Exam

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  1. SPH3U Physics Exam Enduring Expectations Key Understandings

  2. Waves • Two types of waves: linear and longitudinal • Properties of all waves • Universal wave equation: v=fl • resonance

  3. Waves can be classified as linear or longitudinal

  4. Wave Properties • 5 major wave properties exist • transmission • Reflection • Refraction • Diffraction • Interference • Know what happens to v, f and l for each and know at least one real world example for each

  5. frequency • The frequency of a wave is created at the vibrating source • Once established it will not change • Frequency doesn’t change in transmission, reflection, refraction, diffraction or interference.

  6. speed • The speed of the wave changes if the medium changes • Speed changes when a wave refracts. This means the wavelength changes as well • If a wave enters a denser medium the speed decreases and the wavelength decreases.

  7. wavelength • The measured distance from crest to crest • Changes in refraction • Straight waves spread out in diffraction (wavelength doesn’t change … just direction) • Interference creates a new more complex wave but original wavelengths still exist • When reflecting from a more dense material waves undergo a l/2 phase shift

  8. diffraction • Waves spread out when either passing through a small opening or around a hard object • The larger the wave the larger the amount of bending for an object • Ideal amount of bending when the width of the opening equals the wavelength

  9. Applications • Transmission: how your voice carries across a room • Reflection: an echo • Diffraction: noise barriers on sides of roads • Refraction: sonic mirage • Interference: using beat frequency to tune an instrument

  10. Resonance • When an external vibrating source occurs at the natural vibrational frequency of an object the object will experience continual constructive interference --- resonance • Can be viewed as a feedback loop • Applications: MRI, ultrasonic healing/heating/surgery, Wind tunnel testing

  11. UWE- Universal Wave Equation • v=fl • Explains why a medium change has an impact on the wavelength of the wave

  12. Sound • Definition of sound • Human hearing • Air column theory • Air column lab

  13. Definition of Sound • Be prepared to pull definition apart • A LINEAR PRESSURE wave travelling through a MEDIUM at a speed close to 330 m/s.

  14. Human Hearing

  15. 3 Separate areas • Outer, middle, inner • Physics of hearing more important than the biology of the ear … but you need the biology to understand the physics

  16. Outer Ear • External ear, auditory canal, ear drum • Allows for transmission of sound into the inner ear without changing wavelength • External ear: concave reflector • Auditory canal: closed air column • Ear drum: thin easy to vibrate membrane

  17. Middle Ear • Ossicles/ossicular chain • Three tiny bones that work together to: • Transmit sound from ear drum to cochlea • Amplify vibrations because of lever action

  18. Inner Ear • Cochlea • Acts as an analog (vibration) to digital (electrical pulses) converter • Hairs at different lengths resonate at different frequencies • Each hair is embedded in a nerve cell converting mechanical motion into electrical pulses

  19. Air Column • Air column resonance occurs because of reflection of sound off of the bottom surface of the air column • Always has a predictable pattern • Fundamental always at l/4 then an increase of l/2 for successive patterns • Can you • Derive the patterns • Do the math

  20. Two types of air column questions • Given ONE specific point of resonance • A closed air column resonates at the second harmonic …. • Given two successive points of resonance • A closed air column resonates at 17 cm and again at 30 cm ….

  21. One point of resonance • Determine the point of resonance • Fundamental = L1, first harmonic = L2 • Apply the appropriate relationship • L1 = l/4, L2 = 3l/4, L3=5l/4 … • A closed air column resonates at first harmonic with an overall length of 10 cm. The air inside the air column is 20°C. What is the produced frequency?

  22. Two Points of resonance • ALWAYS used in air column experiments • ALWAYS use the DL=l/2 relationship • A closed air column resonates at 10 cm and then again at 27 cm when induced to vibrate by a 1000 Hz tuning fork. What is the temperature inside the column?

  23. Motion/Kinematics • 3 aspects of motion • Vectors • Graphical analysis • Freefall/accelerated motion

  24. Vectors • Magnitude with a direction • Collinear- motion in one dimension • Add/subtract as you would integer values • 100 m/s north plus 50 m/s south = (+100) + (-50) • Orthogonal- forms a right angle triangle • Use trigonometry (SOH CAH TOA) and Pythagorous

  25. Sample Vector Question • The little mermaid wants to swim due north across a stream with a current of 2 m/s. She is capable of maintaining a speed of 2.5 m/s relative to the water. Find: • Her resultant speed if she swims due north and allows the current to push her around • The angle she would have to swim at if she wants to swim due north

  26. Graphical Motion • The slope of the graph can give you the average rate of change or the instantaneous • Slope of a position-time graph = velocity • Slope of a velocity-time graph = acceleration • To convert between graphs you need to calculate the instantaneous rate of change (IROC)

  27. Area under the curve is used to work backwards • Area under an acceleration-time graph = velocity • Area under a velocity-time graph = position • Can you analyze ticker tape? • 6 dots = 0.1 seconds of motion • 60 dots = 1 second of motion • The instantenous rate of change at the centre of an interval = the average on either side of the interval

  28. Reading graphs • Do you know the general shape of: • Constant uniform velocity • Constant acceleration

  29. Constant velocity • Position-time • Straight line … slope of the line = velocity • Velocity-time • Horizontal line … y-value = velocity • Acceleration-time • Straight line along x-axis

  30. Accelerated Motion • Position-time • Smooth curve – shape of curve determines slowing down or speeding up • Velocity-time • Straight line … slope of line = acceleration • Acceleration-time • Horizontal line. Y-intercept = acceleration

  31. Freefall=accelerated motion • If an object is not supported by a surface it will accelerate towards the ground because of gravity • Gravitational acceleration does not depend on mass • Dd=viDt + ½aDt2 • A = (vf – vi)/Dt

  32. Many motion questions can be handled through the conservation of energy idea • If you are asked for the final velocity of an object use the conservation of energy idea • Don’t forget the vector sign convention • Down is negative

  33. An object is dropped from the top of a 20 m cliff. Time? Velocity? • An object is thrown down at 10 m/s from a 20 m cliff. Time? Velocity? • An object is thrown up at 10m/s from a 20 m cliff … what is it’s maximum height?

  34. Forces/Dynamics • Key Understandings • What is a force • Force of gravity – surface • Force of gravity – planetary • Force of friction • Newton’s second law

  35. Forces • A push or pull that can • Move an object • Create pressure • Measured in newtons • A vector quantity so direction is important • Fundamental forces

  36. Fundamental Force • Gravity • Attraction of masses caused by graviton • Weakest force, infinite distance • EM • Attraction of charges caused by electron spin state • Second strongest force, infinite distance • Nuclear Strong • Attraction of sub nuclear particles caused by strong force (colour force) • Strongest force, only acts diameter of nucleus • Nuclear Weak • Dictates radioactivity – neutron decay • Smallest distance of action, second weakest force

  37. Force of gravity – on surface • AKA the weight of the object • Often equals the normal force on the object • Fg=mg

  38. Force of Gravity - planetary • NUG – Newtonian Universal Gravity • Inverse square law • F 1/d2 • If the distance between objects is doubled the force experienced is ¼, if the distance is tripled then the force experienced is 1/9. • Be prepared to use the fact that mass attracts mass in an application setting (tides, grand conjunctions, LaGrange points, etc.)

  39. Force of friction • For this course friction opposes motion • Static = prevents initial motion • Kinetic = tries to bring an object to rest • The amount of friction depends on the types of surfaces in contact and the normal force • Ff = mFN

  40. Newton’s Laws • Law of Inertia – Object at rest will remain at rest, object in motion will remain moving UNLESS acted on by an unbalanced force • Law of Acceleration – an unbalanced force accelerates an object in the direction of the acceleration • FNET =ma • Action-Reaction – Every action force has an equal /opposite reaction force.

  41. Dynamics Problems • Draw a diagram of the situation • Draw a FBD • Use Newton’s second law in the vertical • Use Newton’s second law in the horizontal • Use the components to answer the question

  42. Motion and Force Problems • The acceleration of an object can be used to tie the concepts of motion to the concept of Newton’s second law

  43. A 100 kg crate is pushed with a force of 100 N across a floor of coefficient 0.1. What is the acceleration of the crate? • A 50 kg crate is pushed with an unknown force across a floor of coefficient 0.1. The crate accelerates at a rate of 2 m/s/s. What was the force?

  44. Batman is travelling at a speed of 100 km/h towards a stop sign. He slams on the brake and comes to a complete stop in 10 m. What is the coefficient of friction between the tires and the road?

  45. Energy • The energy is divided into three sections: • Conservation of energy • Thermal Energy • Nuclear Energy

  46. Energy, Work, Power • Energy: ability to do work • Work: a force moving an object through a displacemnt • W = FDd • Power: the rate at which work is done • P = W/t

  47. Conservation of Energy • If the object is moving it has kinetic energy • Ek = ½ mv2 • If the object can drop to a lower position it has stored energy • Ep =mgh • Energy is always conserved: • Total energy at any location EQUALS total energy at all other locations

  48. A crate of Tofu is dropped from a 100 m high cliff. How fast is it travelling when it has reached the halfway in it’s journey?

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