ITEC-I5 Scratch Aug 20091 An intro to Scratch Notes and Tasks for ITEC-I5 Camp Leaving lots of...

ITEC-I5 Scratch Aug 2009 1

An intro to Scratch

Notes and Tasks for ITEC-I5 Camp

Leaving lots of exploration for the future.


What are our goals?

Learn some computing concepts. Use Octave as computing tool. Use Scratch as computing and

multimedia tool. Have fun with Scratch creating

stories, games, art. Learn some computing concepts.


Who computes? Scientists Engineers Businessmen Social scientists Artists FBI agents Brain surgeons Grandkids


Monday concepts (20 min)

What is an algorithm?An algorithm for an average and

minAn algorithm for sorting


Algorithm for computing the average of two numbers

Let the first number be A; say A=12 And the second number be B; say B=15 To compute the average _____________ So the average of 12 and 15 = ________


What algorithm for the average age of two people?

Input this Do precisely this Do precisely that Output what

12

15


problem: finding min Person B is the “ref” watching A. Person A has list of numbered cards, but

cannot look at all the numbers. A can look at 2 numbers at a time only -- one card in each hand. A must find the min of all cards. Exchange roles, with A the “ref” and B

“the player”. HOW TO ALWAYS FIND THE MIN?


Problem: team finding the min Person A can look at no numbers! No numbers can be seen by A, ever! Person B can look at only two numbers on

cards given by person A. Person B gives back to A first the card with

the smaller number (if numbers are = then it doesn’t matter which is given first)

Person A must find the min and show it to the instructor WITHOUT EVER SEEING IT

A and B should switch roles and repeat.


Problem: how to sort?

Use set of cards for each team. How can A sort using B

as comparer?


Sorting two-person game This is a 2-person exercise. To solve the sorting puzzle, person A must form

an ordered list of cards, which the instructor will check for order (this is the OUTPUT).

Person B can only compare two numbers by seeing the numbers. Person B gives A the smaller number card first (precise operations).

Person A can only ask Person B which of two cards has the smaller number. Person A never ever looks at any numbers.

To solve the sorting puzzle, person A must start from an unordered list of cards (this is the INPUT).


Sorting by selecting minimum Spread out list of number cards 31, 22, 13, 32, 11, 21, 23, 33, 12 Select the minimum and begin a new list 11 Select the min of what’s left and add it to

the end of the new list. 11, 12, Repeat this process until the original list is

empty and the new list has all the cards. 11, 12, 13, 21, 22, 23, 31, 32, 33


Problem: what is the average age of our class?

How do we define this? ..compute this?

An algorithm computes some output from the given input using precise steps that a machine can follow


Students use Octave (10 min)

Verify the work and problem solutions as below [while the

instructor leads].


Compute the average of two numbers using Octave

sum = 12 + 15 sum = 27 average = sum/2 average =

13.500

sum is a variable; set its value to 12+15

average is another variable; set its value to the value of sum divided by 2


Octave has many useful ops

It can operate on numbers -- +, /, sqrt It can operate on lists of numbers – min,

max, length, mean Use Octave as needed in camp and after!


gKids = 10 13 11 12 13 >> length(gKids)

ans = 5

>> sum(gKids)

ans = 59

>> avgAge = sum(gKids)/length(gKids)

avgAge = 11.8000

Precise steps to compute the output from the input.

The input is the list of ages; the output is the average of all the ages in the list.

You can use the ages of the actual group present.


sort a list into order >> gKids

gKids = 10 13 11 12 13

>> sort(gKids)

ans = 10 11 12 13 13

>> min(gKids)

ans = 10

>> max(gKids)

ans = 13

>>

What algorithm does MATLAB use to sort the list?

What algorithm finds the min?

What algorithm finds the max?


There are MANY sorting algorithms.

Recursively selecting the min is a BAD algorithm when the list is big. Computer

scientists know many different algorithms, some good for small and some good for

big lists.


Start scratch and let’s go! (90 min)

Click on the cat icon If not on desktop, download

from www.scratch.mit.edu Scratch programming

environment comes up quickly

We will first do simple ops


Goals for Scratch

Learn about objects and behavior Programming motion and sound Programming user interaction Creating your own story, game,

entertainment piece, or simulation (starting Wednesday)


PREFACE These slides are intended to be used in

an active lab demo and discussion and are therefore not complete by themselves.

Scratch has a nice facility for working with sounds; however, during the intro only the instructor’s computer should have speakers. When students get to individual work later, they can use headsets and microphones.


Simple ops first

Sprites are objects We operate on their color, size, position We move them We have them say things


Click on the “Looks” button at the top left.


Major components

At right: the stage with sprite[s] or objects or actors

At left: operations and attributes for the sprites

Center: scripts or program[s] for the behavior[s] of the sprites

Your sprites are actors that you direct with your scripts


The “hello” script Can do it in 57 languages – java, C++,

… Scratch Easy in Scratch: select “Looks”

operations and drag the “hello operation” onto your center panel.

Then double click on this “lego block”: check your sprite behavior at the right

Your very first Scratch program!


Make the cat 50% larger

1. Select “Looks” operations

2. Drag the “change size” operator into your script

3. Click and edit for a 50% change (increase)

4. Double click your one operation script

5. Did your cat sprite get 50% bigger?


Putting a sprite in a location

Motion ops Go to x , y Set x to Set y to Glide to

X is +

Y is +

X is +

Y is -

X is –

Y is -

X is –

Y is +

Origin is (0, 0)


Your sprite’s “attitude”

Choose “Motion” ops

Click on “attitude variables”

Try a “move op” to see changes.

Try “rotation ops” as well.


Locating your sprite

Interesting task: make your own “glide to” operation and have your sprite glide to (200, -100)


Scripting a sequence of ops

Do ops in the following order by dragging operation blocks into a single connected block

Say hello Move 200 steps forward Grow 50% bigger Make the “meow sound”


Result of 4 operation script


Some new operations

• color change (Looks)

• wait (Control)

• move (Motion)


Exercise: write a script to Make the cat move along a square

path Say “hi” at all four corners Wait 3 seconds at each corner Change color at all four corners Double size when back to the

original starting location. Say “That’s all folks” when done.

Show an instructor that you have achieved this.


Using variables

Script might have to remember information

How far is the cat from the dog? How fast is the rocket moving? Where did the user click on the

stage?


Let’s implement an algorithm to average two numbers

Make a variable “number1” (click and drag and set)

Make another one “number2”


Compute average first as sum

Make variable average

Drag a “set operation” to script area

Drag a + operation

Drag variables number1 and number2 to parameters

Click to execute


Average script as 4 operation sequence.

Change the two numbers and click the sequence to execute the block again.


Elements of Scratch: objects Colors Sounds Locations in 2D space Sprites Costumes Variables (to remember the state of

things) Events: that are broadcast for

communication

We want to use Scratch to program with multimedia.


Elements of Scratch: control

Sequence of operations Loops or repetition Detecting events (key or mouse

pressed, sprites overlapping each other, sprites hitting edge of stage, sensor giving value)


Loops are for repeating sequences

Bethoven’s 5th: bump-bump-bam; bump-bump-bam; …

Running the bases in baseball or driving around the block.

Milling around waiting for some event to occur (in the aquarium example, the fish sprites mill around forever)


Loop constructs in Scratch

Repeat N times Repeat forever Repeat forever if

some condition exists (suppose I’m a sprite wandering about this lab until someone asks a question)

Try these!


Exercise: use a loop to

Move sprite around the 4 corners of the square

Wait 2 seconds at each corner Say something at each corner Double size when done Change color when done

Show an instructor that you have achieved this.


Play and examine MadLib

Choose the “file” option at the top of the window

Choose “open”, then “examples” Choose “stories” Choose “MadLib” and then read the

authors instructions Click OK, wait for load, click green

flag


About the MadLib story How many actors (sprites)? What is the role of the girl? How are the answers you give

'remembered' and then used in later actions?

What is the role of the little whale? What makes the little whale flip around? What makes the big whale spout?


Tuesday: computing distances and directions (30 min)

How to go from here (A) to there (B)? Computing distance Computing direction or heading How useful in Scratch or navigation,

etc.?


Angles are importantAbout 30 degrees

About 45 degrees

90 degrees

(right angle)

180 degrees

(straight angle)

360 deg complete circle

215 deg

http://www.mathsisfun.com/geometry/degrees.html

To see animation of angle measure.


Using a protractor to measure angles


Measure some angles with a protractor

P

Q

A

B

C


The treasure is buried under an oak tree 42 degrees to the right of the line between the statue and post

statue

42 deg

post


Right triangles are special

C A

B

What is the distance from point A to point B?

Do this on graph paper.

Draw the triangle ABC with side CB = 3 and side CA = 4.

Cut a “ruler” out of graph paper to measure the side AB.

3

4


Measure another triangle

A

B

5

12C

A person walks north 5 miles from A to C and then east 12 miles from C to B for a total of 17 miles. How far would the person walk going directly from A to B?

(Do this on a scale drawing.)


Pythagorean theorem

Long ago Pythagorus discovered that in a right triangle, with short sides a and b, the long side c is such that c times c is equal to axa + bxb

The scare crow said it in the Wizard of Oz: “In a right triangle, the square of the hypotenuse is equal to the sum of the squares of the other two sides”.

ab

chypotenuse

c x c = a x a + b x b

This is of great use in engineering and navigation.


Shortest distance from A to B?

It’s 65 miles going north from A to C and then east from C to B.

What if we go the direct path from A to B along a straight line?

40

25

A

BC


Scratch script: distance A to B

Pick point A with the mouse

Pick point B with the mouse

Compute the distance from A to B

Test separately!


Test the first part separately

We ask the user to click the mouse. We use variables Ax and Ay to save the mouse click position, then move our sprite there (156, 82) and change its color.


Test the second part (point B)

After double clicking on our second code segment, our sprite has moved from A, where both x and y were positive, to B where both x and y are negative. Our variables are displayed.

B = (-99,-51)


Test the final distance comp.

Executing the above code, results in the stage at the right. Our sprite has moved a distance of 287.6 in going from point A to point B. (Extra: In what direction did it move?)


exercises Solve the distance

problem by changing the script to not use mouse input.

Just set (Ax, Ay) to (0,0) and (Bx, By) to (25, 45) and execute!

Find a distance on the earth using your actual GPS reading from your geocaching unit.


Shortest distance from A to B?

Solve the distance problem by changing the script to not use mouse input.

Just set (Ax, Ay) to (0,0) and (Bx, By) to (25, 45) and execute!

40

25

A

BC

How far A to B?


Using Octave to solve it(You can use a scale drawing too.) >> b = 40 % declare variable b to have value 40 miles

b =40

>> a = 25 % declare variable a to have value 25 miles

a =25

>> cSquared = a * a + b * b % compute the square of the hypotenuse (long side)

cSquared =2225

>> c = sqrt(cSquared) % we need the square root of 2225

c = 47.1699

>> c * c % the square root times itself must be 2225 it is!

ans =2225 % the direct route is about 47 and 1/6 miles; much less than 65


Tuesday: Scratch more

More about control in Scratch. How to control sprite behaviors?How to control user interactions?


Conditions can be checked Do something if

sprite k hits sprite m

Do something if a certain key is pressed

Do something is some variable takes a certain value


Interacting with your sprite or story

Using mouse Entering a character Asking the user a question


Sprite follows the mouse

Try changing the number of steps or the wait time.


Sprites can interact with each other Can detect when colors overlap in space Can detect when sprites bump into edge

of the stage Later: See “bouncing balls” example

under Simulations under Examples Interact with this simulation Check out the rather complex

scripts


Simple communicating sprites

Dog talks to cat in “forever” (infinite) loop Dog sprite sends a message to the cat sprite Cat sprite says “hello” and gives the floor back to the

dog


Cat sprite reacts to dog


exercises A) modify the above scripts so that a

global variable is used to count how many times the dog says “Hello”

B) change the control so that when “Hello” is said 10 times by the dog, the script stops with the dog saying “That’s all folks”.

C) change the scripts so that each sprite moves to a random position on the stage before saying “Hello”

Show your work to an instructor when you get finished with each part .


Check out the break dance example

Open examples; music and dance; break dance

How does break dancing begin? What are the roles of the sprites? What events are in the scripts? What should happen when the

boom box is clicked?


Wednesday Goals

Computing directions or headings in Scratch or Octave (30 min)

Studying Scratch examples done by others (50 min).

Design a project: story, game, simulation, or entertainment/art to do by Friday. (Sketch your plans in your journal and discuss with instructor.)


Wednesday: practical trig

1) Scale drawings 2) Angles and distances

3) Using trig functions


Heading from point A to point B

Suppose my GPS says I am at x=10; y=5

My treasure is at x=22 and y=10

What is my heading and how far do I travel?

**

*

(10, 5)

(22, 10)

E

N


Make a scale drawing and measure the angle and distance.


Tangent of an angle

60

30

A

B

C

2010

20B3

C3 C2

B2

Do you see THREE similar triangles? All share the vertex and angle A. Are there more?


Tangent of an angle

60

30

A

B

C

2010

20B3

C3 C2

B2

10/20 = 0.5 = ½

20/40 = 0.5 = ½

30/60 = 0.5 = ½

15/30 = 0.5 = ½ where is this triangle?

5/10 = 0.5 = ½ where is this triangle?


Tangent of an angle

60

30

A

B

CC2

B2

If C2 is distance 47 from A, how long is side B2-C2? _____

If B3-C3 has length 12, how long is A-C3 ? _______

12

B3

C3


Tangent of an angle is its RISE divided by its RUN

Carpenters use the terms RISE and RUN to measure how steep a roof angle is.

All roofs making the same angle, have the same ratio RISE/RUN

Size of the house doesn’t matter!

run

rise

Tangent of angle = rise/run

= “slope”


Using the hypotenuse and one leg

10 more minutes and a few slides needed to do this

>> rise = 6 rise = 6

>> hyp = 10 hyp = 10

>> angleA = asind(rise/hyp)

angleA = 36.8699 >> sind (36.8699) %in degree

ans = 0.6000

A C

B

Hyp = 10 Rise

= 6

sin A = rise / hyp


What’s the distance from A to C?

Use the Pythagorean Theorem to compute it.

10^2 = b^2 + 6^2

Use the cosine to compute it.

cosine A = run / hyp

run = hyp * cosine A


Problem: angles and sides

Draw any right triangle Measure one side Measure one angle What is the missing angle? ______ What are the missing sides? ____ ____ Check the Pythagorean relation ______ Check the sind and cosd relations ___

___


Angles in Octave >> rise = 20

rise =20

>> run = 40

run = 40

>> angle = atand(rise/run) % function or operator atand gives your angle in degrees

angle = 26.5651

>> rise = 30

rise =30

>> angle = atand(rise/run)

angle = 36.8699


Angles in Scratch


Computing the angle

Execute each of the 3 code segments.

Slope is 0.5 or ½

The angle is about 27 degrees.


Heading from point A to point B

Suppose my GPS says I am at x=10; y=5

My treasure is at x=22 and y=10

What is my heading and how far do I travel?

**

*

(10, 5)

(22, 10)

E

N


Use atand to compute heading

>> east = 22-10 % miles east = 12 >> north = 10-5 % miles north = 5 >> angle = atand(east/north) angle = 67.3801 % head 67 degrees east of

north


Using a different triangle >> rise = 10-5 %miles rise = 5 >> run = 22-10 %miles run =12 >> angle = atand(rise/run) angle = 22.6199 % head about 23 degrees north

of east


Exercises in computing angles

A) Repeat the above Octave solutions in Scratch

B) Find the angles A at the right (angle C=90)

A

C20

30

50

24

CA

CA

45 36


Exercises in Scratch (50 min) Do some of the triangle exercises – any

of them from geocaching? Study the aquarium program to see how

the various fish behave; change fish color and observe the change; change its speed and observe; what other behavior changes can be made?

Students study and modify existing Scratch programs; students imagine creating a program of their own.


Student Scratch project

Pick a project: story, game, simulation, or entertainment/art to

do by Friday. (Sketch your plans in your journal and discuss with

instructor.)


Experiment with Scratch as time permits Thur and Fri

Try your own scripts: make moves, sounds, interactions in simple cases

Try the examples and learn what makes them work

Download Scratch on your own machine and experiment some more

Direct a story; or a simulation; or create a video game.

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ITEC-I5 Scratch Aug 20091 An intro to Scratch Notes and Tasks for ITEC-I5 Camp Leaving lots of...

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