为什么我的pygame球在使用类的时候没有加速？

class Ball:
    def __init__(self, x, y, speed):
        self.x = x
        self.y = y
        self.speed = speed

    def update(self):
        self.x += self.speed

ball = Ball(100, 100, 1)  # 创建球对象

while True:
    # 处理事件
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            pygame.quit()
            sys.exit()

    # 更新球的位置
    ball.update()

    # 绘制球
    pygame.draw.circle(screen, (255, 0, 0), (ball.x, ball.y), 10)

    pygame.display.flip()

class Ball:
    def __init__(self, x, y, speed):
        self.x = x
        self.y = y
        self.speed = speed

    def update(self):
        self.x += self.speed

    def accelerate(self, amount):
        self.speed += amount

ball = Ball(100, 100, 1)  # 创建球对象

while True:
    # 处理事件
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            pygame.quit()
            sys.exit()

        if event.type == pygame.KEYDOWN:
            if event.key == pygame.K_SPACE:
                ball.accelerate(1)  # 按下空格键加速球

    # 更新球的位置
    ball.update()

    # 绘制球
    pygame.draw.circle(screen, (255, 0, 0), (ball.x, ball.y), 10)

    pygame.display.flip()