PY1007: Physics for Engineers I

Transcription

1 PY1007: Physics for Engineers I LECTURES: TUESDAY Kane Building G1 THURSDAY Lecturers Dr. Richard Green (me!) r.green@ucc.ie 1 st Floor, Kane (Science) Building Dr. Síle Nic Chormaic (Module Coordinator) Direct all queries to: s.nicchormaic@ucc.ie Room 216a, 2 nd Floor, Kane (Science) Building

2 RECOMMENDED TEXTBOOKS Physics by Cutnell and Wiley Publisher: John Wiley & Sons Paper version available to buy in the college book shop in Áras na Mac Léinn. Students are advised to buy the electronic version of this book for 20 more details will be given out next week. This will provide you with a host of study aids for the course. Copies of book are also in the college library or second-hand copies may be available from second year students. If you BUY the book (new or second hand) please inform Dr. Nic Chormaic next week or by at s.nicchormaic@ucc.ie

3 Items needed for Laboratory. Physics Laboratory lists should be available on the notice boards on the first floor in the Kane Building (Science) by Wednesday 22 nd September. Notice boards are just in front of the lifts. 1) one laboratory instruction manual available at your first lab session 2) pad of A4 size lined paper 3) pad of A4 sized graph paper 4) one standard A4 loose -leaf binder with two 8 cm binding clips (available from Student Centre bookshop) 5) drawing instruments including pencil, eraser, transparent ruler, etc. 6) electronic pocket calculator 7) small stapler

4 Greek Symbols We will use Greek letters to denote many quantities in physics. For example we use q and f for angles, n for frequency, l for wavelength etc. This table will help you to learn the symbols that we use throughout the course. Please refer back to it regularly.

5 What is Physics? Science and engineering are based on measurements and comparisons. How can we measure things (better and better)? Length, time, mass,... Use the international system of units (SI UNITS) Base quantities and their units: length meter m mass kilogram kg time second s electrical current ampere A thermodynamic temperature kelvin K amount of substance mole mol luminous intensity candela cd + derived units: power(watts, W), etc yotta Y zetta Z exa E peta P tera T 10 9 giga G 10 6 mega M 10 3 kilo k 10 2 hecto h 10 1 deca da 10-1 deci d 10-2 centi c 10-3 milli m 10-6 micro µ 10-9 nano n pico p femto f atto a zepto z yocto y

6 Example: Length 1 meter 1792, France: one ten-millionth of the distance from the north pole to the equator, iron bar kept in Paris 1875, France: upgraded to a bar made from platinum/iridium 1960: 1,650, wavelengths of orange-red light, in a vacuum, produced by burning the element krypton (Kr-86) 1983: The meter is the length of the path travelled by light in vacuum during a time interval of 1/ of a second.

7 Mathematical Tools: Trigonometry Use mathematics to describe how physical universe works. h sinq o h sinq h o h cosq h a h tanq h h o a These are numbers without units, because each is a ratio of the lengths of two sides of a right triangle. Note: Symbol q (theta) is usually used to indicate angles.

8 Mathematical Tools: Vectors Some quantities are scalar and some are vector. A scalar quantity is described by magnitude only: Volume of water in a swimming pool is 50 m 3 Winning time of a race is 12 seconds A vector quantity is described by magnitude and direction: The car drove 2 km west I lifted the box 1 m up off the ground We use arrows to denote the direction and magnitude of a vector: The magnitude is the length of the arrow The direction in which the arrow points is the vector direction

9 Mathematical Tools: Vectors We'll use underline to denote vectors, they can also be represented using boldface or with an arrow. e.g. displacement can be represented as r, r or Displacement of a particle, P, relative to some origin 0 is indicated by the vector r r y 0 Φ θ r x P r : (r,θ) r : (x,y) i.e. vector r is described by magnitude (length) r = r and direction i.e. vector r is described by x and y x r cosq two possible systems of coordinates x r cosq sinq x and y are the components of the vector y r y r sinq or y r cosf Note: Symbol f (phi) is usually used to indicate angles.

10 Mathematical Tools: Vectors The displacement vector r can be written as the sum of two vectors x and y. The magnitudes of x and y are the components of the vector. In other words, adding the two vectors x + y, yields the vector r.

11 Adding Vectors A r 1 r 3 r 2 B r 1 = displacement of A relative to 0 r 2 = displacement of B relative to A 0 r 3 = displacement of B relative to 0 Definition: Sum of two displacements y c y b y a y a c b 1) vectors add by the triangle rule (tail-to-head) 2) components add algebraically x a x b x c x

12 Vectors A vector is any quantity for which the addition rule is the same as the addition rule for displacements. a -a 0 0 The negative of any vector a is -a. Going up the ladder has displacement D, going down has displacement -D. Addition/subtraction of two vectors Scalar multiplication, by some number, c b b+a a b -a -a a ca b (ca) a, ca =c a Vector ca is parallel to a length

13 Summary Lecture 2 We will use SI units to describe measurements e.g. measure length/distance using the meter (m), measure time using the second (s), measure mass using the kilogram (kg). A scalar quantity is described by magnitude only e.g. time, mass. A vector quantity is described by magnitude and direction e.g. velocity, displacement. Sum of two displacements (vector addition) Greek symbols introduced: q (theta) usually represents an angle f (phi) usually represents an angle