FixedUpdate vs Update in Unity - Hands-On Comparison

FixedUpdate vs Update in Unity

📖 Scenario: You are making a simple Unity game where a ball moves based on player input. You want to understand how to use Update and FixedUpdate methods correctly to move the ball smoothly and with proper physics.

🎯 Goal: Build a Unity script that moves a ball using Update for input reading and FixedUpdate for applying physics movement.

📋 What You'll Learn

Create a Rigidbody variable to control the ball's physics

Use Update to read horizontal input into a variable

Use FixedUpdate to apply movement to the Rigidbody

Print messages in both Update and FixedUpdate to see when they run

💡 Why This Matters

🌍 Real World

Games often need smooth and realistic movement. Using <code>Update</code> and <code>FixedUpdate</code> correctly helps make player controls responsive and physics stable.

💼 Career

Understanding Unity's update methods is essential for game developers to create smooth gameplay and avoid bugs related to physics and input timing.

1

Setup Rigidbody variable

Create a public Rigidbody variable called rb inside the BallController class.

Unity

using UnityEngine;

public class BallController : MonoBehaviour
{
    // Create a public Rigidbody variable called rb
    // Your code here
}

Need a hint?

Use public Rigidbody rb; inside the class.

2

Read input in Update

Add a private float variable called horizontalInput. In the Update method, set horizontalInput to Input.GetAxis("Horizontal"). Also, add a Debug.Log statement inside Update that prints "Update called".

Unity

using UnityEngine;

public class BallController : MonoBehaviour
{
    public Rigidbody rb;

    // Add private float horizontalInput
    // Add Update method to set horizontalInput and print message
    // Your code here
}

Need a hint?

Use Input.GetAxis("Horizontal") to read left/right input.

3

Move Rigidbody in FixedUpdate

Add a FixedUpdate method. Inside it, create a Vector3 called movement with horizontalInput as the x value and 0 for y and z. Then call rb.MovePosition(rb.position + movement * 5f * Time.fixedDeltaTime). Also add a Debug.Log statement that prints "FixedUpdate called".

Unity

using UnityEngine;

public class BallController : MonoBehaviour
{
    public Rigidbody rb;
    private float horizontalInput;

    void Update()
    {
        horizontalInput = Input.GetAxis("Horizontal");
        Debug.Log("Update called");
    }

    // Add FixedUpdate method to move rb and print message
    // Your code here
}

Need a hint?

Use rb.MovePosition inside FixedUpdate to move the ball smoothly with physics.

4

Print final messages

Add a print statement in Update that prints the current horizontalInput value. Add a print statement in FixedUpdate that prints the current rb.position.

Unity

using UnityEngine;

public class BallController : MonoBehaviour
{
    public Rigidbody rb;
    private float horizontalInput;

    void Update()
    {
        horizontalInput = Input.GetAxis("Horizontal");
        Debug.Log("Update called");
        // Print horizontalInput value
        // Your code here
    }

    void FixedUpdate()
    {
        Vector3 movement = new Vector3(horizontalInput, 0f, 0f);
        rb.MovePosition(rb.position + movement * 5f * Time.fixedDeltaTime);
        Debug.Log("FixedUpdate called");
        // Print rb.position
        // Your code here
    }
}

Need a hint?

Use print with f-strings to show values in console.