The discussion centers around the relationship between speed and friction, particularly in the context of vehicles on a road. Participants explore various factors affecting friction, including rolling resistance, fluid resistance (drag), and the implications of speed on these forces. The conversation touches on theoretical aspects, practical observations, and the complexities involved in understanding these dynamics.
Participants express differing views on the behavior of rolling resistance and fluid resistance at various speeds. While some agree on the distinction between these types of resistance, there is no consensus on how they interact with speed or their implications for vehicle acceleration.
Participants acknowledge the influence of multiple factors on friction and resistance, including vehicle design, environmental conditions, and mechanical properties. The discussion highlights the complexity of these interactions without resolving the various claims made.
Hootenanny said:For large objects traveling at high speeds the magnitude of the drag force is considered to be proportional to the square of the velocity of the car.
Whether the drag is linear or quadratic is a fuinction of the Reynold's Number; generally speaking, the drag force is linear at very low speeds, and quadratic (increases as the square of the speed) at higher speeds. Regarding also your question as to whether friction increases at increasing speed, it was noted in the above posts that yes, the air drag increases (air resistance), but also the static friction force between the driving tires and the road also increases at increasing speed. The friction between the road and drive wheel tires is what propels the car forward; It is equal to (u_s)N at max speed without the tires slipping, but it is less than (u_s)N at lower speeds (as you noted, it is 0 when the car is not moving!).gmax137 said:Funny, I was thinking about this recently. Can someone point me to an explanation of why the force goes as velocity squared? I saw something that says at low speeds (laminar) the friction is linear with velocity, but in turbulent conditions it is velocity squared. Is that right? Whats the physical explanation for that?
Thanks
Naty1 said:I am not so sure rolling reistance for an automobile should be considered a constant over a wide range of speeds. There are a number of factors at work inlcuding the aerodynamic shape of the car which may increase the force against the road (or reduce it) and the
effects of heat with speed as well. Racing teams heat their tires, spin them in place, to improve traction...
See wikipeida http://en.wikipedia.org/wiki/Rolling_resistance
Hootenanny said:There is a difference between friction and fluid resistance. The deformation of the car tryes and the road surface results in the so-called rolling resistance between the tyres and the road, which is independent of velocity (i.e. the rolling resistance remains constant regardless of your speed).
However, as Ranger Mike points the car also experience fluid resistance or drag. For large objects traveling at high speeds the magnitude of the drag force is considered to be proportional to the square of the velocity of the car.