1, the marble starts to move from rest under the action of force, and the force changes the motion state of the object.

2. When an external force acts on the ball, the kinetic energy of the ball increases.

3. Elastic collision, momentum conservation and energy conservation of two small balls.

4. When the ball falls from a height, gravity does positive work, and the gravitational potential energy is converted into kinetic energy. When it collides with the ground, the speed decreases, the kinetic energy decreases, the elastic potential energy increases, and the kinetic energy is converted into elastic potential energy; Elastic potential energy is converted into kinetic energy in the process of bouncing, and continues to rise, and kinetic energy is converted into gravitational potential energy.