🏃 Lesson 3.3: Moving Objects with Code

Let's bring an object to life. In this lesson you'll make a cube spin and glide using code — and learn the single most important trick for smooth, fair movement: Time.deltaTime.

🎯 Learning Objectives

Move an object with transform.Translate
Rotate an object with transform.Rotate
Use Vector3 to describe directions
Understand why Time.deltaTime keeps motion smooth and frame-rate independent

Estimated Time: 40 minutes

In This Lesson

Our Target Object

We'll script a simple cube — the humble object from your first scene. It can't show motion in a still image, of course, but pressing Play will make it come alive:

A real Unity render of a single cube on a plane — the object we'll animate with code. — Figure 1: Our subject (real render). By the end of this lesson it will spin and slide under code control.

Rotating with Code

Every script can reach its own GameObject's Transform via the word transform. To spin the object a little every frame, put a Rotate call in Update():

using UnityEngine;

public class Spinner : MonoBehaviour
{
    void Update()
    {
        transform.Rotate(0f, 1f, 0f);   // turn 1 degree around Y each frame
    }
}

Attach this to the cube, press Play, and it spins. But there's a problem hiding in that 1f…

The Time.deltaTime Trick

"1 degree per frame" sounds fine — until you realize different computers run at different frame rates. A fast PC might draw 240 frames per second; a slow one 30. Our cube would spin 8× faster on the fast machine. Unfair and inconsistent!

The fix is Time.deltaTime — the number of seconds since the last frame. Multiply your movement by it and you get a consistent "per second" speed on every machine:

public class Spinner : MonoBehaviour
{
    public float speed = 90f;   // degrees per SECOND

    void Update()
    {
        transform.Rotate(0f, speed * Time.deltaTime, 0f);
    }
}

📖 Definition

Time.deltaTime: the time in seconds that the last frame took. Multiplying movement by it converts "per frame" into "per second," so motion looks the same regardless of frame rate.

💡 Golden rule: any movement or rotation inside Update() should be multiplied by Time.deltaTime. Say it with me: "times delta time." You'll write it hundreds of times.

Moving with Translate

To slide an object, use transform.Translate. Directions are given as a Vector3 — three numbers for X, Y, Z. Unity provides handy shortcuts like Vector3.forward and Vector3.up:

public class Glider : MonoBehaviour
{
    public float speed = 3f;   // units per second

    void Update()
    {
        // move forward (along +Z) at 'speed' units per second
        transform.Translate(Vector3.forward * speed * Time.deltaTime);
    }
}

Shortcut	Direction
`Vector3.forward`	+Z (into the screen)
`Vector3.up`	+Y (upward)
`Vector3.right`	+X (to the right)
`new Vector3(1, 0, 0)`	A custom direction (here, +X)

Hands-on Exercise

🏋️ Exercise: Spin and glide

Add the Spinner script (with Time.deltaTime) to a cube. Press Play — it spins smoothly.
In the Inspector, change Speed to 180 — it now spins twice as fast. Try -90 to reverse.
Add a Glider script too, and watch the cube spin and drift forward.

💡 It spins wildly fast / not at all

Wildly fast usually means you forgot * Time.deltaTime. Not at all usually means the script isn't attached or Speed is 0.

✅ Challenge solution: bob up and down

void Update()
{
    float y = Mathf.Sin(Time.time * 2f) * 0.5f; // gentle wave
    transform.position = new Vector3(0f, 1f + y, 0f);
}

🎯 Quick Quiz

Question 1: Why multiply movement by Time.deltaTime?

Question 2: Which reaches the current object's Transform inside its own script?

Summary

🎉 Key Takeaways

transform.Rotate(...) spins an object; transform.Translate(...) moves it.
Directions use Vector3 (X, Y, Z), with shortcuts like Vector3.forward.
Always multiply per-frame motion by Time.deltaTime for smooth, fair speed.
Expose speed as a public field to tune motion in the Inspector.

🚀 What's Next?

Code doesn't always work first time — and that's fine. Lesson 3.4 shows you how to read the Console and squash the errors every beginner hits.