Final answer:
The forces acting on a lightweight ball thrown horizontally are gravity and air resistance.
Step-by-step explanation:
When a lightweight ball is thrown horizontally, the forces acting on the ball just after being released from the thrower's hand are:
- Gravity: The force of gravity acts vertically downwards on the ball, causing it to accelerate downwards. This force is responsible for the vertical motion of the ball.
- Air Resistance: In ideal conditions without air resistance, there are no additional forces acting on the ball in the horizontal direction after it is thrown. However, in the real world, air resistance will affect the speed of the ball in both directions.