A boy is riding a bicycle in a rainy day. The force exerted by the boy and the force due to which rain falls downward.

To understand the forces at play in this scenario, we can consider two main forces: the force exerted by the boy riding the bicycle, and the force due to gravity causing rain to fall downward.

1. Force exerted by the boy riding the bicycle:
The force exerted by the boy on the bicycle can be broken down into two components: the force of propulsion and the force due to friction.

- Force of propulsion: When the boy pedals the bicycle, he exerts a force on the pedals, which causes the bicycle to move forward. This force is usually generated by pushing down on the pedals using leg muscles. The force of propulsion propels the bicycle forward, overcoming the resistance from factors like air resistance and rolling friction.
* Note: Air resistance can increase when it is raining, as the raindrops in the air create additional drag.

- Force due to friction: As the boy rides the bicycle, there are various forms of friction acting against his motion. Rolling friction is present between the tires and the road surface, which resists the bicycle from sliding. Additionally, there may be friction in the bicycle's chain, gears, and other moving parts. The boy's efforts must overcome these frictional forces in order to propel the bicycle forward.

2. Force of gravity causing rain to fall downward:
Raindrops are formed through a process called condensation, where water vapor in the atmosphere forms into liquid droplets. These droplets are subject to the force of gravity, causing them to fall downward towards the Earth's surface. Gravity is an attractive force that pulls objects with mass, like raindrops, towards the center of the Earth.

In summary, as the boy rides the bicycle on a rainy day, he exerts a force of propulsion by pedaling and overcomes forces of friction to move forward. At the same time, raindrops fall downward due to the gravitational force acting on them.