UK K12 GCSE A-Level Year 3 KS2 Computer Science Scratch Events Loops and Sprites

Learning objectives

By the end of this topic, students will be able to:

• Understand the concept of events in Scratch, including how to create and handle events using the "when green flag clicked" block.
• Explain the purpose of loops in Scratch, including the different types of loops (forever, until, repeat) and how to use them to create repeating actions.
• Describe the use of sprites in Scratch, including how to create and manipulate sprites, and how to use sprites to create animations.
• Design and implement a Scratch project that incorporates events, loops, and sprites to achieve a specific goal.

Core concepts

Events

In Scratch, an event is something that happens in a program that can trigger a reaction. Events can be triggered by the user, such as clicking a button, or by the program itself, such as a timer going off. In Scratch, events are created using the "when" blocks, which are used to specify what action will trigger the event.

For example, the "when green flag clicked" block is an event that is triggered when the user clicks the green flag to start the program. This event can be used to create a reaction, such as making a sprite move or play a sound.

Loops

A loop is a way of repeating a set of actions in a program. Loops are used to create repeating patterns, such as animations or music. There are three types of loops in Scratch:

• Forever loop: This type of loop will repeat indefinitely until the program is stopped.
• Until loop: This type of loop will repeat until a certain condition is met.
• Repeat loop: This type of loop will repeat a certain number of times.

For example, a forever loop can be used to create a sprite that moves back and forth across the screen indefinitely.

Sprites

A sprite is a visual object in a Scratch program that can be manipulated and controlled. Sprites can be used to create characters, animals, or other objects that can move, interact, and react to events.

In Scratch, sprites are created using the "make a clone of" block, which creates a copy of a sprite. Sprites can also be manipulated using the "move" and "turn" blocks, which change the position and direction of the sprite.

Worked examples

Example 1: Creating a sprite that moves when clicked

In this example, we will create a sprite that moves across the screen when the user clicks the mouse.

1. Create a new sprite by clicking on the "make a clone of" block.
2. Name the sprite "car" and change its color to red.
3. Use the "when flag clicked" block to create an event that will trigger the sprite to move.
4. Use the "move 10 steps" block to make the sprite move 10 steps to the right.
5. Repeat steps 3-4 to create a repeating pattern of movement.

Example 2: Creating a loop that repeats a sound

In this example, we will create a loop that repeats a sound indefinitely.

1. Create a new sound by clicking on the "make a sound" block.
2. Name the sound "beep" and set its duration to 1 second.
3. Use the "forever" loop to create a repeating pattern of the sound.
4. Use the "play sound beep" block to play the sound.

Example 3: Creating a sprite that interacts with another sprite

In this example, we will create a sprite that interacts with another sprite by moving towards it.

1. Create two new sprites by clicking on the "make a clone of" block.
2. Name the first sprite "car" and the second sprite "target".
3. Use the "when flag clicked" block to create an event that will trigger the car to move towards the target.
4. Use the "move towards" block to make the car move towards the target.
5. Repeat steps 3-4 to create a repeating pattern of movement.

Common misconceptions

• Misconception 1: Thinking that events only happen when the user interacts with the program.
• Misconception 2: Thinking that loops only repeat a set of actions a fixed number of times.
• Misconception 3: Thinking that sprites only move in a straight line.

Exam tips

• Tip 1: Make sure to use the correct blocks to create events, loops, and sprites.
• Tip 2: Use the "when" blocks to create events that trigger reactions.
• Tip 3: Use the "forever" loop to create repeating patterns.
• Tip 4: Use the "move" and "turn" blocks to manipulate sprites.
• Tip 5: Use the "make a clone of" block to create new sprites.

MCQs with explanations

MCQ 1 [F]

What type of loop repeats indefinitely until the program is stopped? A) Forever loop B) Until loop C) Repeat loop D) While loop

Correct answer: A) Forever loop

Why the distractors fail:

• B) Until loop repeats until a certain condition is met, not indefinitely.
• C) Repeat loop repeats a certain number of times, not indefinitely.
• D) While loop is not a valid type of loop in Scratch.

MCQ 2 [H]

What is the purpose of the "when flag clicked" block? A) To create a new sprite B) To make a sprite move C) To trigger an event D) To repeat a set of actions

Correct answer: C) To trigger an event

Why the distractors fail:

• A) The "make a clone of" block creates a new sprite.
• B) The "move" block makes a sprite move.
• D) The "repeat" block repeats a set of actions.

MCQ 3 [F]

What is the name of the block that creates a new sprite? A) Make a clone of B) Move C) Turn D) Flag clicked

Correct answer: A) Make a clone of

Why the distractors fail:

• B) The "move" block makes a sprite move.
• C) The "turn" block changes the direction of a sprite.
• D) The "flag clicked" block triggers an event.

MCQ 4 [H]

What type of loop repeats a certain number of times? A) Forever loop B) Until loop C) Repeat loop D) While loop

Correct answer: C) Repeat loop

Why the distractors fail:

• A) Forever loop repeats indefinitely until the program is stopped.
• B) Until loop repeats until a certain condition is met.
• D) While loop is not a valid type of loop in Scratch.

MCQ 5 [F]

What is the purpose of the "move towards" block? A) To make a sprite move away from another sprite B) To make a sprite move towards another sprite C) To make a sprite move in a straight line D) To make a sprite turn around

Correct answer: B) To make a sprite move towards another sprite

Why the distractors fail:

• A) The "move away" block makes a sprite move away from another sprite.
• C) The "move" block makes a sprite move in a straight line.
• D) The "turn" block changes the direction of a sprite.

Short-answer questions

Question 1

Explain the difference between a forever loop and a repeat loop.

Question 2

Describe the use of the "when flag clicked" block in a Scratch program.

Question 3

Explain how to create a sprite that moves towards another sprite.

Question 4

Describe the use of the "make a clone of" block in a Scratch program.

Question 5

Explain the purpose of the "move towards" block in a Scratch program.