The Physics Involved in Altering the Speed of a Heavy Car

 

Driving home from college for winter break with my dad, my sister, one of my friends, one of my sister’s friends, and all of our luggage, it was undeniable that the car resisted when my dad tried to alter the vehicle’s speed. My dad kept commenting on how much effort it took to accelerate the car with its larger mass and that he could feel an actual pull of the car resisting to changing speed. Newton’s Second Law of Motion states that force is equal to mass multiplied by the acceleration, and thus, based on this law, a larger force is necessary to accelerate a car with a larger mass. In order to change the speed of the car, either by accelerating or braking, my dad had to exert a greater force by pressing harder on the accelerator and the brakes. A greater force needs to be applied to a car with a larger mass so that it accelerates in the same manner as a lightweight car. We also noted that it took more time to adjust the speed of the car, which makes sense as a car with a larger mass has a greater moment of inertia, meaning a heavier car is more resistant to change. The equation for the moment of inertia is I=mr^2, and thus the moment of inertia and mass are directly proportional. The car tended to go downhill faster than normal, since the larger mass of the car caused a larger magnitude of gravitational force. Furthermore, pressing a foot on the brakes causes the car to apply friction to the wheels, which opposes the car’s motion, and thus leads to the car slowing down.