- Grant enables UAB Hospital staff to feed underprivileged moms of newborns
- Military man coming to UAB for first time, graduates Saturday
- UAB’s College of Arts and Sciences to honor distinguished alumni and friends
- ‘Tis the season of giving — UAB launches holiday blood drive
- How a cybersecurity expert protects his smartphone
- ASC presents Take 6, “The Most Wonderful Time of the Year” Dec. 15
- Leeth named UAB School of Medicine assistant dean for strategic planning
- Coping with holiday grief
- New water plan saves big money
- Campus police offer holiday safety tips
- Alys Stephen Center Screens Walking the Camino: Six Ways to Santiago
- Hospital feeds underprivileged new moms
- UAB’s Alys Stephens Center presents Yo-Yo Ma Dec. 6
- Southern Miss tops Blazers, 62-27, in season ending game
- Henry Panion selected for 2014 Alabama African-American History Calendar
Physics of a Car’s Suspension
Cars are the meeting point for many areas of scientific achievement. Although advances in mechanical engineering have undoubtedly had the most effect in the advancement the automobile, the car as we know it today wouldn’t be be possible without the work of chemical engineers working on the creation of fuel systems and tire compounds; metallurgists and materials scientists designing new lighter and stronger materials for car components; and less obviously, manufacturing engineers who enable the mass production of these supremely technical machines.
One of the most important factors that determine the performance of the car is the suspension. When most people think of performance cars, you think fast, big engines, and roaring exhaust notes. While this is important, the ability for a car to have effective contact with the road is even more important, and when you consider the types of motion a car undergoes whether it be acceleration or deceleration in a straight line, around turns, or god forbid, on straight or winding bumpy roads, you begin to realize that suspension may be as if not more important than zero to sixty times or top speed.
A car’s suspension is most simply defined as the sum to total of the effects of the springs, dampers, and sway bars. Each tire has it’s own spring and damper with the sway bars connecting the front tires, and rear tires parallel to each axle.
The springs are usually the first thing that come to mind when a car’s suspension is considered. In physics, a spring will oppose any force that moves the spring from an equilibrium point which can be most simply described as a certain length. So if you have a one foot spring, any force that stretches it or compresses it will be opposed by the force of the spring. So if you smoothly, compress this spring (push it to a length less than one foot), then smoothly return it to its equilibrium length, force of the spring will increase during compression, and then decrease as you take it back to equilibrium. If, however, you compress it, then let the spring go, then it will snap back to equilibrium. The problem with this is that a spring will overshoot its equilibrium point and return to a length greater than one foot. Of course, this is no bueno, so the spring will tend to snap back to equilibrium a second time in which it will over shoot this point, and this cycle will continue in a type of motion called harmonic motion, which is most simply described as what happens when a spring goes boing.
So a spring opposing compression in a car is good, but this boinging is bad. Imagine how rough a ride through Birmingham would be if your springs were always in harmonic motion. To stop this from happening, each spring assigned to each tire has a damper which changes the springs kinetic energy to heat thus deadening all motion. This allows a spring to compress, and return to its equilibrium length with no boing. This means that as a tire goes over a bump in the road, the tire will sink into the wheel well, the spring will then push the tire back to an equilibrium length during which a damper will soak up some of the springs energy to end the motion at the equilibrium point.
The final part of the equation is the sway bar which is another type of spring called a tortional spring. This spring essentially stops a tire on one side of the car from being compressed to a height that’s different from the tire on the opposite side of the car, and is most important when a car is turning. During a fast turn, a car’s body will tend to shift to one side and you feel this as a force pulling you towards the outside of the car which is a centripetal force. During this body roll, the springs on the tires on the outside of the turn are compressed more than those on the inside of the turn. In order to keep this body roll to a minimum, sway bars will actually resist any force on the outside of the turn that is compressing these tires.
In race cars, springs, dampers, and sway bars are very stiff, which maximizes performance, but makes for a very jarring ride. In road cars and commuter cars, however, the components are much softer which allows for more body roll in corners, and more boing on rough roads which makes for a floaty kind of ride. The opposite side of the spectrum from race cars, are off road vehicles which have even softer suspension components in order to for each tire to have sufficient contact with the road and to absorb the shock of landing big jumps.
Next time you’re on your grocery run, make sure to take a second and appreciate the engineers who developed the complex suspension systems that make your ride both comfortable and safe.