Jump with an Impulse

Part of the Physics and Gameplay section of Coddy's Unity journey. Lesson 3 of 71.

AddForce takes a second argument, a ForceMode, that says how to use the vector. Without it you get ForceMode.Force, a push that lasts one physics step, so it has to be added step after step. A kick, a jump or an explosion happens all at once, and that is ForceMode.Impulse: the whole push in one go, changing the speed by the impulse divided by the mass.

This football (0.5 kg) is kicked on a click. Its speed jumps by (0, 2, 6) / 0.5 = (0, 4, 12) m/s at the next physics step, and gravity and the grass take over from there:

void Update()
{
    if (Input.GetMouseButtonDown(0))
    {
        rb.AddForce(new Vector3(0, 2, 6), ForceMode.Impulse);
    }
}

A one-off push can be called from Update(), on the frame of the click: Unity keeps it and applies it at the next physics step. The four modes differ in two ways, all at once or over a step, and with or without the mass:

Force: over a step, divided by mass (engines, wind).
Acceleration: over a step, mass ignored.
Impulse: all at once, divided by mass (kicks, jumps).
VelocityChange: all at once, mass ignored: the vector is added straight to the speed.

Challenge

Easy

Make the frog jump once per press of Space.

Below the comment, write if (Input.GetKeyDown(KeyCode.Space)).
Inside it, call rb.AddForce(Vector3.up * jumpImpulse, ForceMode.Impulse);, so the frog's 2 kg count.

Press Play and press Space: the frog hops up and falls back. Then Check.

Try it yourself

using UnityEngine;

public class FrogJump : MonoBehaviour
{
    public float jumpImpulse = 10f;
    private Rigidbody rb;

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

    void Update()
    {
        // Space: one upward kick of jumpImpulse
    }
}

All lessons in Physics and Gameplay

1Rigidbody

Gravity and Mass Push with AddForceJump with an ImpulseFixedUpdate for Physics Velocity Kinematic Bodies Recap: Launch Pad

4Coroutines

Invoke InvokeRepeating, CancelInvoke Your First Coroutine Loops in Coroutines Stopping Coroutines Recap: Countdown

7Rotation

Euler Angles Quaternions Face the Way You Move Turn Smoothly Recap: Turret

10Project: Arena Escape

Open After the Last Wave

Practice on your own: Unity playground