为什么Physics2D会为AddForce（）与速度产生不同的结果？

Question

为什么Unity2D的Physics2D引擎中的 Gravity 在交替实现这两行代码时会有所不同？

例如，我已将我的播放器精灵附加到播放器控制器C＃脚本：

private float speed = 500f;
RigidBody2D playerChar = null;

然后让我的角色走：

Vector2 vec = new Vector2 (Input.GetAxis("Horizontal"), 0);
playerChar.AddForce(vec * speed);

重力设定为50

结果1：我的角色头像正常掉落。

与此同时：

Vector2 vec = new Vector2 (Input.GetAxis("Horizontal"), 0);
playerChar.velocity  = (vec * speed);

重力仍然设定为50

结果2：我的角色现在需要很长时间才会摔倒（它慢慢地“漂浮”下来）。

为什么？

Answer 1

This is because you're forcing the y component of the rigidbody's velocity to zero.

When you add force, it adds, it doesn't replace.

When you set the velocity, you're specifically setting it to a Vector2 that has a y value of 0, gravity then kicks in on the fixed update cycle and adds a small amount of gravity, causing your player to fall slowly. Then Update happens again and you force the y value back to 0 once more.