Backward Force Experienced by the Boy Sitting at the Back Seat of a Car

Introduction
When a car accelerates forward, the passengers inside may experience a sensation of being pushed backward. This is due to the inertia of their bodies. In this case, the boy sitting at the back seat of the car experiences a backward force.

Explanation
The following points explain why the boy experiences a backward force:

1. Newton's First Law of Motion: Law of Inertia
- According to Newton's First Law of Motion, an object at rest tends to stay at rest, and an object in motion tends to stay in motion with the same speed and in the same direction, unless acted upon by an external force.
- When the car starts moving forward, the boy sitting at the back seat tends to stay at rest due to inertia. Therefore, he resists the forward motion of the car.

2. Frictional Force
- The backward force experienced by the boy is due to the frictional force between the seat and the boy's body.
- As the car accelerates forward, the seat exerts a forward force on the boy to move him along with the car.
- However, due to inertia, the boy resists this forward force, causing a backward force to be exerted on him by the seat.

3. Newton's Third Law of Motion: Law of Action and Reaction
- According to Newton's Third Law of Motion, for every action, there is an equal and opposite reaction.
- When the seat exerts a forward force on the boy, the boy exerts an equal and opposite backward force on the seat.
- This backward force experienced by the boy is a reaction to the forward force exerted on him by the seat.

Conclusion
In conclusion, when the driver of the car starts moving it in the forward direction, the boy sitting at the back seat experiences a backward force. This is due to the combination of his inertia resisting the forward motion of the car and the frictional force between the seat and his body. Additionally, this backward force is in accordance with Newton's First and Third Laws of Motion.