How to Add Force in Unity: Simple Rigidbody Example

In Unity, you add force to an object by calling Rigidbody.AddForce(Vector3 force) on its Rigidbody component. This method applies a force vector that moves the object physically in the game world.

Syntax

The basic syntax to add force in Unity is:

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

Here:

• rigidbody is the Rigidbody component attached to your game object.
• Vector3 force is the direction and strength of the force.
• ForceMode (optional) defines how the force is applied (default is Force).

csharp

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

Example

This example shows how to add a forward force to a Rigidbody when the space key is pressed. It moves the object forward smoothly.

csharp

using UnityEngine;

public class AddForceExample : MonoBehaviour
{
    private Rigidbody rb;

    void Start()
    {
        rb = GetComponent<Rigidbody>();
    }

    void FixedUpdate()
    {
        if (Input.GetKeyDown(KeyCode.Space))
        {
            Vector3 forceDirection = transform.forward * 500f;
            rb.AddForce(forceDirection);
        }
    }
}

Output

When you press the space key, the object moves forward with a sudden push.

Common Pitfalls

Common mistakes when adding force in Unity include:

• Not having a Rigidbody component on the object, so AddForce does nothing.
• Using very small force values that don't move the object noticeably.
• Forgetting that AddForce is affected by mass and drag of the Rigidbody.
• Using AddForce in Update() instead of FixedUpdate() for physics consistency.

Always check your Rigidbody setup and apply forces in FixedUpdate() for smooth physics.

csharp

/* Wrong: Adding force in Update() repeatedly */
void Update()
{
    rb.AddForce(Vector3.forward * 10f);
}

/* Right: Adding force once or in FixedUpdate() */
void FixedUpdate()
{
    if (Input.GetKeyDown(KeyCode.Space))
    {
        rb.AddForce(Vector3.forward * 500f);
    }
}

Quick Reference

Tips for adding force in Unity:

• Use Rigidbody.AddForce() to move objects physically.
• Choose ForceMode based on effect: Force, Impulse, VelocityChange, or Acceleration.
• Apply forces in FixedUpdate() for stable physics.
• Ensure the object has a Rigidbody component.

Key Takeaways

Use Rigidbody.AddForce with a Vector3 to apply physical force to objects.

Apply forces inside FixedUpdate() for consistent physics behavior.

Ensure your object has a Rigidbody component before adding force.

Adjust ForceMode to control how the force affects the object.

Small forces or missing Rigidbody cause no visible movement.