Marcus Wilson With help from Alison Campbell Faculty of Science and Engineering

1. Scholarship Preparation (Physics) October 2011 Marcus Wilson With help from Alison Campbell Faculty of Science and Engineering

2. Introductions Me, You

3. Today • What is scholarship about? • Some exercises to get you thinking properly • How to answer physics questions • Time at end for free questions, but ask them as we go, too • I am assuming you are already very familiar with the subject material • I am not a scholarship (or NCEA) examiner. But I do know physics

4. Group work • I will get you to work in groups a lot today • I strongly suggest you work with some people you don’t know. They will have been taught by different teachers and this may give you new insights into the physics. • I know it’s scary, but you will benefit from it

5. Scholarship 2011 • Will be challenging and demanding for the most able students in each subject • Will be awarded to the best students in each of the Scholarship subjects. • Number of awards will be about 3% of the number of students entered in Level 3 of the subject. • Awards are used for allocating money and recognising excellence.

6. What makes for success in Scholarship exams?

7. A student receiving Scholarship in a subject will have demonstrated: • High level critical thinking, abstraction and generalisation; and • The ability to integrate, synthesise and apply knowledge, skills, understanding and ideas to complex situations.

8. A student receiving Scholarship in a subject will have demonstrated: • High level critical thinking, abstraction and generalisation; and • The ability to integrate, synthesise and apply knowledge, skills, understanding and ideas to complex situations. All scholarship questions will be in strange settings…

9. Markers’ report on Scholarship Physics 2010 • Most candidates had a serious attempt at this exam • Successful candidates clearly had an appropriate knowledge of physics But… • Many candidates did not carefully read all parts of the question

10. 2010. What successful students did well: • Could analyze everyday use of physics ideas • Showed a wide range of relevant physical understanding • Approached mechanics problems by applying the appropriate laws of Newtonian Mechanics • Understood capacitors and inductors

11. Unsuccessful students: • Lacked the conceptual and algebraic skills needed • Made guesses based on general intuition, not physics understanding • Missed out or made limited attempts at many questions • Couldn’t apply Newton’s laws correctly • Struggled with centripetal force

12. Key physical concepts Let’s look at the questions… I hope you have already done this: http://www.nzqa.govt.nz/qualifications-standards/awards/scholarship/scholarship-subjects/scholarship-physics/

13. 2010 Q1. Nuclear Physics Q2. Inductors with a.c. and d.c. Q3. Capacitors with d.c. Q4. Waves, diffraction and interference Q5. Simple harmonic motion Q6. Mechanics (Circular motion and Newton’s laws) Quick link to 2010 paper

14. 2009 Q1. Electrons (Bohr model, electric/magnetic fields) Q2. a.c. electricity Q3. Mechanics (energy, kinematics) Q4. Mechanics (energy, rotational inertia and energy) Q5. Waves and diffraction Q6. Mechanics (Newton’s laws) Quick link to 2009 paper

15. 2008 Q1. Light (photons and waves) Q2. Mechanics (rotational statics, torques) Q3. Mechanics (angular momentum, energy) Q4. Doppler effect Q5. Mechanics (gravity, kinematics, energy) Q6. d.c. circuits Quick link to 2008 paper

16. 2007 Q1. Oscillations and waves Q2. Mechanics (Statics, angular momentum) and Nuclear Q3. Waves and resonance Q4. Mechanics (circular motion) Q5. Mechanics (Newton’s laws) Q6. Circuits (induction) Quick link to 2007 paper

17. So… questions about: mechanics, circuits (a.c. and d.c.), waves, … Brain overload: This seems to cover a huge amount of information But what do you already know?

18. Task 1

19. Brainstorming: work in groups to write down all the concepts you know that relate to mechanics.

20. What was the point of all that? You know the information already (a lot of it too) For scholarship you need to be able to apply it And the situations will be unfamiliar

21. Task 2

22. Example question to get you applying… The Bungy Jump I want to jump off a bridge (yeah, right) and just be able to touch the water at the bottom. In your groups, discuss what the bungy-crew needs to know to make this happen?

23. Example question to get you applying… The Bungy Jump Unfamiliar situation. What physics is happening? I want to jump off a bridge (yeah, right) and just be able to touch the water at the bottom. In your groups, discuss what the bungy-crew needs to know to make this happen?

24. Now lets get more mathematical • OK, so let’s say: • Bridge is 75 m high • My mass is 65 kg • Acceleration due to gravity is 9.8 m/s2 • For purposes of this example, assume bungy is massless (it definitely isn’t, but that makes it a very hard problem) • Unstretched bungy is half the height of the bridge (i.e. it kicks in when I am half the distance to the water) • So approximately what is the bungy’s spring constant? And what is the maximum upward force the bungy exerts on me?

25. Some mechanics trapsNewton’s Laws • We all think we know what Newton’s laws are • But do we?

26. From 2011 scholarship paper

27. What does constant velocity tell us?

28. Newton’s second law • If you know force, you know acceleration • Does a question become a bit easier if you substitute the word ‘force’ for ‘acceleration’, or ‘acceleration’, for ‘force’?

29. Newton’s third law(Oh how difficult it is…) • A book lies motionless on a table. Gravity exerts a force mg downwards on the book. The table exerts a normal force N upwards on the book. What does Newton III tell us? N mg

30. Who said the two are equal and opposite?

31. Who said the two are equal and opposite? • For every action there is an equal and opposite reaction. • The two (action and re-action) are on different objects • The two (action and re-action) are the same type of force (e.g. gravity and gravity, friction and friction, electrostatic and electrostatic…)

32. The gravitational pull of the earth exerts a force on the book – the book in turn exerts a gravitational force on the earth. An action-reaction pair • The book exerts a contact force on the table. The table exerts a contact force on the book. An action-reaction pair • N = mg is an example of Newton’s first law, not third: the book is at rest, so the forces must be balanced.

33. Circular motion • A car is travelling around a circular track at constant speed v. As viewed by the ‘eye’ X v X

34. Which of the following shows the forces on the car? A. Normal Normal Normal Centripetal force Friction Centrifugal Friction Friction between tyres/road Centripetal D. B. Gravity Gravity Gravity E. No forces – they all cancel C. Centripetal

35. Centripetal force is not a magic force • Circular motion does not cause a centripetal force to appear magically • A resultant force towards the centre is what causes circular motion • This force is always physical – friction in the case of the car If something is moving in a circle (at constant speed) we can conclude that the vector sum of forces on the object must point towards the centre (and have value mv2/r)

36. How to answer physics questions

37. A. What is the question About? • What concepts am I going to need to answer the question? • What physics principles might I need to draw from? • Think! B. Bring the concepts together • Identify all the steps to your solution • Write them out in rough first C. Compose your response • Write out your answer clearly and completely…

38. What is this question About? • Bring those concepts together • Compose a response 2007 Scholarship exam

39. (c) Explain why the roller eventually travels at a constant velocity

40. Composing Answers Answer the question, the whole question, and nothing but the question OR…Read the question, and answer the question. Think: How many marks will you get for a question (or part-question) you don’t attempt? How many marks do you get for a page of perfectly correct stuff, but stuff that the question didn’t ask for?

41. Composing Answers Know where you are going… Think and Plan before you write – don’t brain dump The examiner doesn’t know what’s in your head – only what he can interpret from your answers Keep you maths logical – show all necessary steps

42. Composing Answers Don’t leave room for mis-interpretation Use your physics terminology correctly Don’t use ‘weight’ when you mean ‘mass’ Don’t use ‘momentum’ when you mean ‘angular momentum’ Don’t talk about the flow of voltage Don’t miss out units

43. Know your equations and how to use them You need to know the context and meaning of every one of these If you know your equations, you can easily pick the correct ones. Equation-spotting won’t help you at scholarship – it will just tell the examiners you don’t know what you are talking about

44. Know your equations and how to use them You need to know the context and meaning of every one of these If you know your equations, you can easily pick the correct ones. Equation-spotting won’t help you at scholarship – it will just tell the examiners you don’t know what you are talking about What does  = /t mean? Why the minus sign?

45. Let’s put all this together

46. First thought: What the %$j+!”: do I know about phugoid oscillations?

47. First thought: What the %$j+!”: do I know about phugoid oscillations? Second thought: What ^%@(*! equation do I use to find the force for a phugoid oscillator. We didn’t do that in class. It’s not fair.

48. Equation-spotting won’t help you. But knowing your physics will.

49. Equation-spotting won’t help you. But knowing your physics will. Unfamiliar situation. What physics is happening?

50. Equation-spotting won’t help you. But knowing your physics will. Third thought. What is the question About?