Bridging the Gap between Mathematics and the Physical Sciences

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1 Bridging the Gap between Mathematics and the Physical Sciences Department of Mathematics Oregon State University

2 Mathematics vs. Physics Math vs. Physics Functions Dot Product Dictionary

3 Mathematics vs. Physics Math vs. Physics Functions Dot Product Dictionary

4 Mathematics vs. Physics Math vs. Physics Functions Dot Product Dictionary

5 What are Functions? Math vs. Physics Functions Dot Product Dictionary Suppose the temperature on a rectangular slab of metal is given by T(x, y) = k(x 2 + y 2 ) where k is a constant. What is T(r, θ)?

6 What are Functions? Math vs. Physics Functions Dot Product Dictionary Suppose the temperature on a rectangular slab of metal is given by T(x, y) = k(x 2 + y 2 ) where k is a constant. What is T(r, θ)? A: T(r, θ) = kr 2

7 What are Functions? Math vs. Physics Functions Dot Product Dictionary Suppose the temperature on a rectangular slab of metal is given by T(x, y) = k(x 2 + y 2 ) where k is a constant. What is T(r, θ)? A: T(r, θ) = kr 2 B: T(r, θ) = k(r 2 + θ 2 )

8 What are Functions? Math vs. Physics Functions Dot Product Dictionary Suppose the temperature on a rectangular slab of metal is given by T(x, y) = k(x 2 + y 2 ) where k is a constant. What is T(r, θ)? A: T(r, θ) = kr 2 B: T(r, θ) = k(r 2 + θ 2 ) r θ x y

9 What are Functions? Math vs. Physics Functions Dot Product Dictionary MATH T = f (x, y) = k(x 2 + y 2 ) T = g(r, θ) = kr 2

10 What are Functions? Math vs. Physics Functions Dot Product Dictionary MATH T = f (x, y) = k(x 2 + y 2 ) T = g(r, θ) = kr 2 PHYSICS T = T(x, y) = k(x 2 + y 2 ) T = T(r, θ) = kr 2

11 What are Functions? Math vs. Physics Functions Dot Product Dictionary MATH T = f (x, y) = k(x 2 + y 2 ) T = g(r, θ) = kr 2 PHYSICS T = T(x, y) = k(x 2 + y 2 ) T = T(r, θ) = kr 2 Two disciplines separated by a common language...

12 What are Functions? Math vs. Physics Functions Dot Product Dictionary Differential Geometry! T(x,y) T (x,y) 1 T(r,θ) T (r,θ) 1 S (x,y) T T(x,y) R 2 R Two disciplines separated by a common language...

13 Mathematics vs. Physics Math vs. Physics Functions Dot Product Dictionary Physics is about things. Physicists can t change the problem.

14 Mathematics vs. Physics Math vs. Physics Functions Dot Product Dictionary Physics is about things. Physicists can t change the problem. Mathematicians do algebra. Physicists do geometry.

15 Math vs. Physics Functions Dot Product Dictionary

16 Math vs. Physics Functions Dot Product Dictionary Projection: u v = u v cos θ θ u v = u x v x + u y v y

17 Math vs. Physics Functions Dot Product Dictionary Projection: u v = u v cos θ θ u v = u x v x + u y v y Law of Cosines: ( u v) ( u v) = u u + v v 2 u v u v 2 = u 2 + v 2 2 u v cos θ

18 Math vs. Physics Functions Dot Product Dictionary Projection: u v = u v cos θ θ u v = u x v x + u y v y Law of Cosines: ( u v) ( u v) = u u + v v 2 u v u v 2 = u 2 + v 2 2 u v cos θ Addition Formulas: u = cos α î + sinαĵ v = cos β î + sinβ ĵ u v = cos(α β)

19 Math vs. Physics Functions Dot Product Dictionary Find the angle between the diagonal of a cube and the diagonal of one of its faces.

20 Math vs. Physics Functions Dot Product Dictionary Find the angle between the diagonal of a cube and the diagonal of one of its faces. Algebra: u = î + ĵ + ˆk v = î + ˆk = u v = 2 Geometry: u v = u v cos θ = 3 2 cos θ

21 Math vs. Physics Functions Dot Product Dictionary Find the angle between the diagonal of a cube and the diagonal of one of its faces. Algebra: u = î + ĵ + ˆk v = î + ˆk = u v = 2 Geometry: u v = u v cos θ = 3 2 cos θ Need both!

22 Math vs. Physics Functions Dot Product Dictionary Kerry Browne (Ph.D. 2002)

23 Math vs. Physics Functions Dot Product Dictionary CUPM MAA Committee on the Undergraduate Program in Mathematics Curriculum Guide CRAFTY Subcommittee on Curriculum Renewal Across the First Two Years Voices of the Partner Disciplines

24 Bridge Project Vector Differentials Gradient The Bridge Project

25 Bridge Project Vector Differentials Gradient The Bridge Project Differentials (Use what you know!) Multiple representations Symmetry (adapted bases, coordinates) Geometry (vectors, div, grad, curl)

26 Bridge Project Vector Differentials Gradient The Bridge Project Differentials (Use what you know!) Multiple representations Symmetry (adapted bases, coordinates) Geometry (vectors, div, grad, curl) Small group activities Instructor s guide Online text (

27 Vector Differentials Bridge Project Vector Differentials Gradient dy ĵ d r dx î d r = dx î + dy ĵ

28 Vector Differentials Bridge Project Vector Differentials Gradient dy ĵ d r dx î r dφ ˆφ d r dr ˆr d r = dx î + dy ĵ d r = dr ˆr + r dφ ˆφ

29 Vector Differentials Bridge Project Vector Differentials Gradient dy ĵ d r dx î r dφ ˆφ d r dr ˆr d r = dx î + dy ĵ d r = dr ˆr + r dφ ˆφ ds = d r d A = d r 1 d r 2 da = d r 1 d r 2 dv = (d r 1 d r 2 ) d r 3

30 Gradient Bridge Project Vector Differentials Gradient

31 Gradient Bridge Project Vector Differentials Gradient Master Formula: df = f d r

32 Gradient Bridge Project Vector Differentials Gradient Master Formula: df = f d r f = const = df = 0 = f d r df ds = f d r d r

33 The Hill Bridge Project Vector Differentials Gradient Suppose you are standing on a hill. You have a topographic map, which uses rectangular coordinates (x,y) measured in miles. Your global positioning system says your present location is at one of the points shown. Your guidebook tells you that the height h of the hill in feet above sea level is given by h = a bx 2 cy y 0-5 where a = 5000 ft, b = 30 ft mi 2, and c = 10 ft mi x

34 Coherent Calculus Definition Differentials

35 Coherent Calculus Definition Differentials co-he-rent: logically or aesthetically ordered

36 Coherent Calculus Definition Differentials coherent: logically or aesthetically ordered cal-cu-lus: a method of computation in a special notation

37 Coherent Calculus Definition Differentials coherent: logically or aesthetically ordered calculus: a method of computation in a special notation differential calculus: a branch of mathematics concerned chiefly with the study of the rate of change of functions with respect to their variables especially through the use of derivatives and differentials

38 Differentials Definition Differentials d(u + cv) = du + c dv d(uv) = u dv + v du

39 Differentials Definition Differentials d(u + cv) = du + c dv d(uv) = u dv + v du d (u n ) = nu n 1 du d (e u ) = e u du d(sin u) = cos u du d(cos u) = sinu du d(ln u) = 1 u du

40 Derivatives Definition Differentials Derivatives: f (x) = sin(x) = f (x) = cos(x)

41 Derivatives Definition Differentials Derivatives: d d sinu sinu = du du = cos u

42 Derivatives Definition Differentials Derivatives: Chain rule: d d sinu sinu = du du = cos u h(x) = f ( g(x) ) = h (x) = f ( g(x) ) g (x)

43 Derivatives Definition Differentials Derivatives: Chain rule: d d sinu sinu = du du d d sinu sinu = dx dx = d sinu du = cos u du dx = cos u du dx

44 Derivatives Definition Differentials Derivatives: Chain rule: Inverse functions: d d sinu sinu = du du d d sinu sinu = dx dx = d sinu du = cos u du dx g(x) = f 1 (x) = g (x) = = cos u du dx 1 f ( g(x) )

45 Derivatives Definition Differentials Derivatives: Chain rule: Inverse functions: d d sinu sinu = du du d d sinu sinu = dx dx = d sinu du = cos u du dx = cos u du dx d du lnu = d du q = dq du = 1 du/dq = 1 de q /dq = 1 e q = 1 u

46 Derivatives Definition Differentials Instead of: chain rule related rates implicit differentiation derivatives of inverse functions difficulties of interpretation (units!)

47 Derivatives Definition Differentials Instead of: chain rule related rates implicit differentiation derivatives of inverse functions difficulties of interpretation (units!) One coherent idea:

48 Derivatives Definition Differentials Instead of: chain rule related rates implicit differentiation derivatives of inverse functions difficulties of interpretation (units!) One coherent idea: Zap equations with d

49 Derivatives Definition Differentials Instead of: chain rule related rates implicit differentiation derivatives of inverse functions difficulties of interpretation (units!) One coherent idea: Zap equations with d & Corinne A. Manogue, Putting Differentials Back into Calculus, College Math. J., (to apppear).

50 Functions A Radical View of Calculus The central idea in calculus is not the limit. The central idea of derivatives is not slope. The central idea of integrals is not area. The central idea of curves and surfaces is not parameterization. The central representation of a function is not its graph.

51 Functions A Radical View of Calculus The central idea in calculus is not the limit. The central idea of derivatives is not slope. The central idea of integrals is not area. The central idea of curves and surfaces is not parameterization. The central representation of a function is not its graph. The central idea in calculus is the differential. The central idea of derivatives is rate of change. The central idea of integrals is total amount. The central idea of curves and surfaces is use what you know. The central representation of a function is data attached to the domain.

52 SUMMARY Functions

53 SUMMARY Functions I took this class a year ago, and I still remember all of it...

54 Functions

Bridging the Gap between Mathematics and the Physical Sciences

Bridging the Gap between Mathematics and the Physical Sciences Department of Mathematics Oregon State University http://www.math.oregonstate.edu/~tevian Mathematics vs. Physics Math vs. Physics Functions