Simple Example. Slow object down.

import pygame

FRICTION = 20

class ImageHandler:
    def __init__(self):
        self.ball = self.create_ball(30, 'dodgerblue')

    def create_ball(self, diameter, color):
        size = diameter + 1, diameter + 1
        r = diameter // 2
        surface = pygame.Surface(size, pygame.SRCALPHA)
        surface.fill((0, 0, 0, 0))
        pygame.draw.circle(surface, color, (r, r), r)
        return surface

class Ball(pygame.sprite.Sprite):
    def __init__(self, image, velocity, position, anchor):
        super().__init__()
        self.image = image
        self.rect = image.get_rect(**{anchor: position})
        self.center = pygame.Vector2(self.rect.center)
        self.vector = pygame.Vector2()
        self.velocity = 0
        self.max_velocity = velocity

    def move(self, movement):
        self.center += movement
        self.rect.center = self.center

    def shoot(self, event):
        self.vector = (event.pos - self.center).normalize()
        self.velocity = self.max_velocity

    def update(self, delta):
        if self.velocity > 0:
            self.move(self.vector * self.velocity * delta)
            self.velocity -= FRICTION * delta

class Game:
    def __init__(self, caption, size, flags=0, fps=60):
        pygame.display.set_caption(caption)
        self.display = pygame.display.set_mode(size, flags)
        self.rect = self.display.get_rect()
        self.clock = pygame.time.Clock()
        self.running = False
        self.delta = 0
        self.fps = fps

        self.image = ImageHandler()
        self.ball = Ball(self.image.ball, 100, self.rect.center, 'center')
        self.sprites = pygame.sprite.Group(self.ball)

    def on_draw(self, surface):
        surface.fill('black')
        self.sprites.draw(surface)

    def on_event(self, event):
        if event.type != pygame.QUIT:
            if event.type == pygame.MOUSEBUTTONDOWN:
                if event.button == 1:
                    self.ball.shoot(event)
        else:
            self.running = False

    def on_update(self, delta):
        self.ball.update(delta)

    def run(self):
        self.running = True
        while self.running:
            for event in pygame.event.get():
                self.on_event(event)

            self.on_update(self.delta)
            self.on_draw(self.display)
            pygame.display.flip()
            self.delta = self.clock.tick(self.fps) / 1000

pygame.init()
game = Game("Slowing Down Ball", (800, 600))
game.run()
pygame.quit()