Bob accelerates away from a stop sign. His teddy bear is on the passenger seat. On whom does the back of the seat exert a greater force?
To determine whether the back of the seat exerts a greater force on Bob or the teddy bear, we need to understand the concept of an accelerating reference frame.
When a car accelerates, Bob, the teddy bear, and the seat experience an acceleration in the forward direction. In this case, there are two forces that act on Bob and the teddy bear: the force of gravity (their weight) and the force exerted by the back of the seat.
According to Newton's second law of motion, the net force acting on an object is equal to its mass multiplied by its acceleration (F = ma). Thus, the force experienced by an object depends on its mass and the acceleration it undergoes.
Assuming both Bob and the teddy bear have the same mass, the net force on each of them depends solely on the acceleration they experience. Since both objects are in the same car, they undergo the same acceleration, so the net force on them due to the car's acceleration is equal.
However, there is an additional force acting on Bob, which is the force his body exerts on the seat due to his inertia. This force is greater than the force exerted on the teddy bear since Bob has a greater mass. By Newton's third law of motion, the seat exerts an equal but opposite force on Bob. Therefore, the back of the seat exerts a greater force on Bob compared to the teddy bear.
So, in summary, the back of the seat exerts a greater force on Bob as he experiences an additional force due to his own inertia.