Question

A fly slams into the front windshield of an approaching car. How does the impact force on the fly compare to the impact force on the car. Which object, the fly or the car, experiences a greater acceleration? Explain.

Answer 1

When two objects collide, either of them exerts an impulse force on the other one. This force, however, is same in magnitude, and opposite in direction, according to Newton's third law of motion, which says :

"Every action has an equal and opposite reaction".

Thus, we can conclude that, the impact force on the fly is equal to that on the car.

We know, force equals mas times acceleration of an object. Since, the mass M of the car is much greater than that of the fly, say, m, the acceleration A of the car will not be equal to that of the fly, say a.

Mathematically, since the impact forces are equal, ma = MA.

Hence, (a / A ) = ( M / m ).

But, M >> m, so, ( M / m ) >> 1.

Thus, ( a / A ) >> 1

or, a >> A.

Hence, the fly will experience a much greater acceleration compared to the car.