A photo taken from my car while driving down the H1 freeway.
After dropping Jordan off at her house at the end of our day together, I returned home via the H1 freeway. On my return trip home, I was actively thinking and trying to decide what I was going to write my physics blog about this week. All of the sudden, because physics is all around us, an idea finally hit me (with quite a bit of force too!).
In an attempt to maintain a speed of exactly 50mph (the speed limit), I put my car on cruise control to ensure that I wouldn’t speed. The cruise control feature worked great while I was traveling on flat ground because it found and maintained a force that caused an acceleration of 0m/s^2, that is, a force that caused net force to be 0. On flat ground, my car maintained a constant velocity of 50mph the entire time. Once I reached the point of the freeway where my car was going down an incline, however, the cruise control feature failed me, as cruise control cannot control breaks.
While the car traveled down the incline, I asked myself, “Why, if the car is exerting the same force as it was before, does it now accelerate?” With simple knowledge of force and inclined planes, this question is easy to answer. Yes, the car exerted the same force down the incline as it exerted before the incline, but it now had the horizontal force of mgx (mgSintheta) pushing it forward as well. The horizontal force of mgx, in this case, caused net force to be greater than zero because the force of the car + mgx was greater than the force of friction that opposed the car’s motion. With net force greater than zero, the car must accelerate because Fnet = ma. Using this equation, we find that, with a constant mass, an increase in net force will cause an increase in acceleration because the two variables are directly related.
Analyzing the effects of inclined planes on net force and on my car’s motion during the drive home, I found, made the lonely car ride home much more phun.
P.S. Jordan says “hi” 🙂
A Day in the Life of Physics 