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# Lesson 2 graphic e magnitudes

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Learn basic issues about graphic expression

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### Lesson 2 graphic e magnitudes

1. 1. GRAPHIC EXPRESSION Lesson 2. 1st term
2. 2. Perspective in drawings • We use projection drawings to represent 3D objects in two dimensions (our paper) • There are two types of projections: Cylindrical (Orthogonal) Conic •No distorsion •Vanishing point (VP) far away •Objects are distorted in the same way our eyes see them •Vanishing point close (x, y, z) VP VP
3. 3. First angle projection • Cylindrical projection composed of three views (taken from very far away) of the object: front side top
4. 4. First angle projection: result front top side
5. 5. Oblique projection • We represent one of the faces (mathing with X and Y axis) in true dimension and the others are distorted. Y Z X
6. 6. Representing objects in oblique projection We have to consider the X, Y and Z axis. We first draw the front face of the figure (X and Y axis Then we draw the sides corresponding with the z axis with a reduction coefficient of 1/2 We finally close the figure with the lines corresponding to the back of the figure Y Z X
7. 7. Axonometric projection _ Isometric projection • Axonometric projection shows an object from the corner so we see its three sides • Objects seem distorted because the same scale is used for all features • One axis is drawn vertical and the others are at an angle. 120º 120º 120º Isometric projection
8. 8. Drawing objects in isometric projection We draw according the axis at 120º angles We first draw a figure’s corner 120º 120º 120º Second we draw the lines which correspond to the sides next to the corner, corresponding with Z axis Then we draw the lines corresponding to the left and rigth corners We first draw a figure’s corner Isometric projection
9. 9. Two point perspective Draw an horizontal line across the page and mark two vanishing points: VP1 and VP2  Draw one corner of the box: vertical line Draw the construction lines from the top and the botton of the corner to the vanishing point  Draw two vertical lines corresponding to the left and rigth corners. They go from the top to the botton lines Draw the last construction lines from the top and the botton of the other corners Complete the box using the construction lines VP1 VP 2
10. 10. Single point perspective First draw the front of the cube. Then add a vanishing point (X) Draw thin construction lines from each corner to the vanishing point Draw the lines which correspond to the back of the figure Draw the rest of the figure over the segments of the construction lines VP
11. 11. Dimensioning • To dimension means “to indicate the real size of an object in its drawing” 70 25 50 45
12. 12. Scale • Scale is a quotient/relationship beetween the size of an object’s drawing and the real size of this object. Scale=Drawing size/real size: 1:n or n:1 It is written as entire number, one of it is 1. Amplification scale: 2:1 (n:1) Reduction scale: 1:2 Real scale: 1:1
13. 13. Magnitudes and units • Magnitude is a physical property which we can measure / determine / quantify: i.e: length, mass,… • Units are the symbols which go after a number and identify the magnitude we refer to
14. 14. Types of magnitudes • Fundamental: we can express or determine them with a direct measurement: there are seven: mass (M), length (L), time (t) • Derived (derivadas): they are obtained by combining the fundamental magnitudes: force, volume, surface…
15. 15. Metric system • A metric system is a unit system where bigger and smaller quantities are easier to convert. In a metric system, units of the same magnitude are transformed into powers of 10. 106 1000 100 mega kilo M K 10 0.1 0.01 0.001 10-6 hecto dam deci centi mili micro H d c m µ D 1
16. 16. The international system (S.I.) • It is a metric system where units are Type Funda- magnitude Unit Length Meter (m) Mass Kilogram (kg) mental Time Second (s) Temperature Kelvin (K) Derived Force Newton (N=kgm/s2 Energy Joule (J=Kgm2/s2 Power Watt (J/s)
17. 17. Conversion coefficients • For different reasons, magnitudes can be expressed into different units. To convert those units we multiply them by conversion coefficients: They are quotients where we write the units we want to convert and their mathematical relationship. i.e 52km 1000 1 m Km 52000 m 1. We identify how many different magnitudes we have: 1 (length) and add the same number of coeff. (1) 2. We write the former unit in the denominator and the new as the numerator 3. Before the unit, we add a “1” before the bigger unit and before the smaller, the number of smaller units contained in the bigger . 4. We simplify and multiply, obtaining the result