How to make Physics in Scratch | Full Tutorial

Summary

This tutorial covers how to create dynamic projectiles with realistic physics in Scratch. Starting with tank and ball sprite creation, the video guides viewers through scripting collisions, motion, and bounciness, using custom blocks and variables. It explains how to add gravity, handle projectile movement, and calculate accurate bounce directions using math concepts like dot products. The tutorial also addresses collision detection with level walls, handling curved surfaces, and refining the simulation with adjustable parameters like projectile speed and gravity. It concludes with a fun challenge to add more gameplay features and improve project interactivity.

Takeaways

• 😀 Create a tank sprite in Scratch that can fire projectiles by positioning it in the center and adding a special invisible rectangle to avoid clipping.
• 😀 Add a level sprite with borders to create boundaries for the gameplay, enhancing the overall environment of the game.
• 😀 For the projectile, use a red circular ball sprite and ensure it is centered and of an appropriate size (16-17 pixels).
• 😀 The tank sprite follows the mouse pointer and fires projectiles when the spacebar is pressed, ensuring a controlled fire rate.
• 😀 Ball projectiles are clones of a hidden original sprite. When fired, the clones move based on the mouse pointer's position and direction.
• 😀 To simulate realistic movement, set the projectile's initial velocity based on the distance between the mouse and the screen center.
• 😀 Implement a repeat loop to destroy projectiles after they travel a certain distance, preventing them from staying forever in the game.
• 😀 Use simple horizontal and vertical bounce logic by negating the projectile's speed in the X or Y direction when it collides with walls.
• 😀 Add gravity to the ball simulation by modifying the Y-speed, creating a more dynamic and bouncy experience for the projectiles.
• 😀 Improve collision detection with curved surfaces by calculating the surface normal and implementing complex bounce physics using vectors and dot product mathematics.
• 😀 Add friction by tweaking the bounce calculation to simulate energy loss during collisions, making the game physics feel more realistic.
• 😀 Prevent the projectiles from getting stuck in walls by adding checks and safeguards in the collision detection loop to ensure smooth gameplay.

Q & A

What is the purpose of creating an invisible rectangle around the tank sprite?

The invisible rectangle is used to avoid the unpleasant clipping effect that occurs at the edges of the sprite, ensuring a smooth experience when interacting with the tank.

Why is it important to position the ball sprite perfectly centered on the screen?

Positioning the ball sprite centered ensures that the projectiles are launched consistently from the tank and in the correct direction, avoiding misalignment during gameplay.

What role does the 'space key' and 'mouse click' play in triggering projectile launches?

The space key and mouse clicks trigger the creation of clones of the ball sprite, which are then launched as projectiles. This allows for user-controlled projectile firing.

How does the projectile's velocity get determined in the script?

The velocity of the projectile is determined by the position of the mouse pointer. The further the mouse is from the center of the screen, the faster the projectile travels in that direction.

What changes are made to the script in order to add collision detection with the level walls?

The script checks if the ball is touching the level walls, and if so, deletes the ball clone. This ensures the projectiles stop once they hit the level boundaries.

What is the importance of using a custom block like 'tick' in the ball sprite?

The 'tick' block is used to handle the main processing of the ball's movement, velocity adjustments, and collision detection, ensuring smooth and efficient gameplay.

How do the ball projectiles bounce off walls in this script?

The projectiles bounce off walls by negating the speed in the x or y direction, depending on which axis the collision occurs along, making the ball change direction after hitting a wall.

What is the purpose of introducing gravity in the ball's behavior?

Gravity is added to simulate more realistic projectile motion, causing the ball to gradually fall downwards and creating a bouncy effect when it collides with surfaces.

Why does the script use a circular collision sweep to calculate surface normals?

A circular collision sweep helps determine the direction of the normal vector, which is necessary for accurately calculating how the ball should bounce off curved surfaces.

What effect does adjusting the bounce coefficient (e.g., setting it to -1.6) have on the projectiles?

Adjusting the bounce coefficient affects the ball's bounciness after collisions. A value of -1.6 creates some energy loss on each bounce, making the ball gradually lose speed and appear less bouncy.