How to Use AddForce in Unity: Simple Guide with Examples

In Unity, use AddForce on a Rigidbody component to apply a force that moves an object physically. Call rigidbody.AddForce(Vector3 force, ForceMode mode) inside a script to push or pull the object in a direction.

Syntax

The AddForce method applies a force to a Rigidbody to move it physically. It has two main parts:

• Vector3 force: The direction and strength of the force.
• ForceMode mode (optional): How the force is applied, like a push or an instant velocity change.

Example syntax:

rigidbody.AddForce(Vector3 force, ForceMode mode);

csharp

rigidbody.AddForce(Vector3 force, ForceMode mode = ForceMode.Force);

Example

This example shows how to push a Rigidbody forward when the player presses the space key. It uses AddForce inside the Update method to apply a force continuously while the key is held.

csharp

using UnityEngine;

public class AddForceExample : MonoBehaviour
{
    public Rigidbody rb;
    public float forceStrength = 500f;

    void Update()
    {
        if (Input.GetKey(KeyCode.Space))
        {
            Vector3 forceDirection = transform.forward * forceStrength * Time.deltaTime;
            rb.AddForce(forceDirection, ForceMode.Force);
        }
    }
}

Output

When you hold the space key, the object with this script moves forward smoothly due to the applied force.

Common Pitfalls

• Forgetting Rigidbody: AddForce only works if the object has a Rigidbody component.
• Wrong ForceMode: Using the wrong ForceMode can cause unexpected movement. For example, ForceMode.Impulse applies an instant push, while ForceMode.Force applies continuous force.
• Ignoring Time.deltaTime: Not multiplying force by Time.deltaTime in Update can cause inconsistent force application.
• Using AddForce in FixedUpdate: It's best to use AddForce in FixedUpdate for physics consistency, but it can work in Update if you multiply by Time.deltaTime.

csharp

/* Wrong way: Applying force without Rigidbody */
// This will do nothing if Rigidbody is missing
// transform.AddForce(Vector3.forward * 10f); // transform does not have AddForce method

/* Right way: Ensure Rigidbody and use AddForce */
Rigidbody rb = GetComponent<Rigidbody>();
if(rb != null) {
    rb.AddForce(Vector3.forward * 10f);
}

Quick Reference

Remember these tips when using AddForce:

• Always attach a Rigidbody to the object.
• Choose the right ForceMode for your effect.
• Use FixedUpdate for physics updates when possible.
• Multiply force by Time.deltaTime if applying force in Update.

Key Takeaways

AddForce moves objects by applying physical forces to their Rigidbody component.

Always ensure the object has a Rigidbody before using AddForce.

Use the correct ForceMode to control how the force affects the object.

Apply AddForce inside FixedUpdate for consistent physics behavior.

Multiply force by Time.deltaTime if applying force in Update to keep movement smooth.