Ask A Scientist
Why does a car, a race car and a big truck makes the noises they do? Do you think the noises are cool? I do!
Asked by: Rachael Klein
School: St. James Middle School
Teacher: Cora Walter
Hobbies/Interests: Horseback riding, school, playing piano, swimming, sewing, Karate(recently spent a week in Japan at a Karate tournament)
Career Interest: Massage therapist or a psychologist
Answer from George Catalano
Professor of mechanical engineering, Binghamton Un
Research area: Turbulence; fluid mechanics; aerodynamics; the impact of technology upon the environment; and engineering ethics
Ph.D. school: The University of Virginia
Family: Married; have two Alaskan malamutes and two more in our hearts
Interests/hobbies: All things Italian, philosophy, cosmology, grand prix racing, writing, painting
To answer such an important question, let us first try to understand what is meant by the term, "noise." We commonly use "noise" to describe sound waves as they impact our ear. We hear noise when a sound wave also known as a pressure wave, impacts the eardrum and causes the eardrum to vibrate, sending further vibrations to the brain. This idea of a sound or pressure wave may seem difficult to imagine. How can we visualize in our mind’s eye what a sound wave actually looks like? One interesting way you can try can occur the next time you stand near a still pond. Pick up a small pebble and toss it into the pond and watch what happens. You will be treated to a series of concentric circles or ripples, generated at the place where the pebble first strikes the pond’s smooth surface. Those circles will gradually grow until they either reach the edge of the pond or simply vanish. The circles represent sound or pressure waves moving away from the pebble or sound source. Every time there is a vibrating surface surrounded by a medium, in this case air, pressure waves or sound is generated. Noise is a particular kind of sound or pressure wave. It is one that has no structure, no rhythm, no beat such as would be found in music or spoken language. Let’s then go back to the car, the truck and the racing car. What generates the noise or those sound or pressure waves? In each case, there are several sources, which include the engines with its gasoline or diesel fuel explosions, moving valves and camshafts and all the other hardware associated with the internal combustion or diesel engine. The rolling of tires over the pavement also generates a large amount of noise. Then there is vibration of the vehicle’s body itself as it moves up and down on its suspension. Lastly there is the aerodynamic noise generated by the rushing of the air past the vehicle as it moves down the road. Each type of vehicle generates its own unique noise signature or pattern. There is one kind of noise unique to the diesel trucks. Have you ever hear an n extremely loud clattering noise as a large truck comes to a rapid stop? That noise, which is another type of pressure or sound wave, is generated by releasing some of the pressure built up inside the diesel engine as it is operating. The release of the pressure greatly decreases the power generated by the diesel and helps bring the truck to a rapid stop without using its mechanical breaks. It is termed an "airbrake." Racing cars with their high performance racing engines without mufflers or any form of sound deadening materials generate perhaps the loudest noise of all the vehicles. The sound of a Ferrari V12, powering a Formula 1 car through a quick lap at places like Watkins Glen is like no other. Perhaps noise, like beauty, is in the ear of the beholder!