Rigidbody

Adding a Rigidbody hands an object over to the physics engine. It now has mass, falls with gravity, gets pushed by other objects and can be moved with forces. It needs a Collider to actually bump into things.

Properties

Methods

ForceMode: which one do I use?

Code Samples

Physics-based player with a jump

using UnityEngine;

[RequireComponent(typeof(Rigidbody))]
public class PhysicsPlayer : MonoBehaviour
{
    [SerializeField] private float moveSpeed = 6f;
    [SerializeField] private float jumpForce = 5f;

    private Rigidbody rb;
    private Vector2 moveInput;
    private bool jumpRequested;

    void Awake()
    {
        rb = GetComponent<Rigidbody>();
        rb.constraints = RigidbodyConstraints.FreezeRotation; // don't fall over
    }

    void Update()
    {
        // 1. Read input in Update (so no key press is missed).
        moveInput = new Vector2(Input.GetAxisRaw("Horizontal"), Input.GetAxisRaw("Vertical"));
        if (Input.GetButtonDown("Jump")) jumpRequested = true;
    }

    void FixedUpdate()
    {
        // 2. Apply physics in FixedUpdate.
        Vector3 move = new Vector3(moveInput.x, 0f, moveInput.y).normalized * moveSpeed;
        // Keep current vertical speed so gravity and jumping still work.
        rb.linearVelocity = new Vector3(move.x, rb.linearVelocity.y, move.z);

        if (jumpRequested)
        {
            rb.AddForce(Vector3.up * jumpForce, ForceMode.Impulse);
            jumpRequested = false;
        }
    }
}

[RequireComponent(typeof(Rigidbody))] makes Unity add a Rigidbody automatically when you add this script, and prevents it from being removed.

A moving platform (kinematic)

using UnityEngine;

public class MovingPlatform : MonoBehaviour
{
    [SerializeField] private Vector3 offset = new Vector3(0f, 0f, 5f);
    [SerializeField] private float speed = 1f;
    private Rigidbody rb;
    private Vector3 start;

    void Awake()
    {
        rb = GetComponent<Rigidbody>();
        rb.isKinematic = true;
        start = rb.position;
    }

    void FixedUpdate()
    {
        float t = Mathf.PingPong(Time.time * speed, 1f);
        rb.MovePosition(start + offset * t);
    }
}

What happens at runtime

Common Mistakes

• Moving with transform.position or transform.Translate. Skips physics: objects tunnel through walls and collisions are jittery. Use linearVelocity, AddForce or MovePosition.
• Calling continuous AddForce in Update. The push then depends on frame rate. Put it in FixedUpdate.
• Old tutorial code doesn't compile. In Unity 6, rb.velocity → rb.linearVelocity, rb.drag → rb.linearDamping, rb.angularDrag → rb.angularDamping.
• Huge mass differences (1 vs 10000) make the simulation unstable. Keep ratios under about 100:1.

See also

• Physics Basics
• Collider
• Physics

This page is a simplified, AI-assisted interpretation. For the complete and authoritative reference, see the official Unity documentation.