When a moving bus suddenly applies brakes, the passengers sitting in it fall in the forward direction. This can be explained by :

When a moving bus suddenly applies brakes, the passengers fall forward due to Newton’s first law of motion, also known as the law of inertia [t2][t5]. This law states that an object in motion will remain in uniform motion in a straight line unless acted upon by an external force [t5]. In this scenario, the lower part of the passenger's body, which is in contact with the bus, stops along with the vehicle due to friction [t1][t8]. However, the upper part of the body tends to maintain its state of motion due to inertia [t1][t2]. Consequently, the upper body continues moving forward while the base remains stationary, resulting in a forward lurch [t2][t3]. This resistance to a change in the state of motion is a fundamental property of matter defined by Newton's first law [t6][t8].

Sources

1. [1] https://www1.grc.nasa.gov/beginners-guide-to-aeronautics/newtons-laws-of-motion/