Evaluation:
The kinetic theory of gases assumes that gases are ideal, thus that there are no interactions between molecules, and the size of the molecules is small compared to the free space between the molecules, but molecules are as a physical body that moves continually through space in random directions.
In a microscopic view, the pressure exerted on the walls of the container is the result of molecules colliding with the walls, and hence exerting force on the walls (Graph 3). When many molecules hit the wall, a large force is distributed over the surface of the wall, which gives pressure.
An important fact derived from the kinetic theory of gases shows that the average kinetic energy of the gas molecules depends only on the temperature. Since average kinetic energy is related to the average speed of the molecules (EK = mu2 / 2, where m=mass and u is the average speed), the temperature of a gas sample must be related to the average speed at which the molecules are moving. Thus, we can view temperature as a measure of the random motion of the particles, defined by the molecular speeds.
This implies that there must be a range (distribution) of speeds for the system. In fact, there is a typical distribution of molecular speeds for molecules of a given molecular weight at a given temperature, known as the Maxwell-Boltzmann distribution (Graph 3). This distribution was first predicted using the kinetic theory of gases, and was then verified experimentally using a time-of-flight spectrometer. As shown by the Maxwell-Boltzmann distributions in Graph 3, there are very few molecules traveling at very low or at very high speeds. The maximum of the Maxwell-Boltzmann distribution shows the intermediate speed at which the largest number of molecules are traveling. As the temperature increases, the number of molecules that are traveling at high speeds increases, and the speeds become more evenly distributed in the curves.
Graph 3
The Maxwell-Boltzmann distribution can be shown graphically as the plot of the number of molecules traveling at a given speed versus the speed. As the temperature increases, this curve broadens and extends to higher speeds.
As seen in Graph 3, there is a unique distribution curve for each temperature. Temperature is defined by a system of gaseous molecules only when their speed distribution is a Maxwell-Boltzmann distribution. Any other type of speed distribution rapidly becomes a Maxwell-Boltzmann distribution by collisions of molecules, which transfer energy. Once this distribution is achieved, the system is said to be at thermal equilibrium, and hence has a temperature.
When a body hits the steering wheel directly, the force of this impact is distributed over a small area of the body, resulting in injuries to this area. The area that hits the steering wheel is shown in red.
When a body is restrained by an airbag, the force of the impact is distributed over a much larger area of the body, resulting in less severe injuries. The area that hits the airbag is shown in orange.
Conclusion:The law of inertia, is demonstrated in a car collision and it is Newton's first law which states that: objects moving at a constant velocity continue at the same velocity unless an external force acts upon them. When a car stops suddenly, as in a car incident, a body inside the car continues moving forward at the same velocity as the car was moving prior to the collision, because its inertial tendency is to continue moving at constant velocity. However, the body does not continue moving at the same velocity for long, but rather comes to a stop when it hits some object in the car, such as the steering wheel or dashboard. Thus, there is a force exerted on the body to change its velocity. Injuries from car accidents result when this force is very large. Airbags protect you by applying a restraining force to the body that is smaller than the force the body would experience if it hit the dashboard or steering wheel suddenly, and by spreading this force over a larger area. For simplicity, in the discussion below, we will consider only the case of a driver hitting the steering wheel. If there is a restraining device as an airbag, the force of impact decreases, hence, the airbag reduces the rate of deceleration. Therefore, the force on the body is smaller and fewer injuries result.
When an airbag restrains the body, the body exerts an equal and opposite force on the airbag. Unlike the immovable steering wheel, the airbag is deflated slowly. This deflation can occur because of the presence of vents in the bag. The force exerted by the body pushes the gas through the vents and thus deflates the bag. Because the gas can only leave at a certain rate, the bag deflates slowly.
Additionally, airbags help reduce injuries by spreading the force over a larger area. If the body crashes directly into the steering wheel, all the force from the steering wheel will be applied to a localized area on the body that is the size of the steering wheel, from which a serious injury can form. However, when the body hits an airbag, which is larger than a steering wheel, all the force from the airbag on the body will be spread over a larger area of the body. Therefore, the force on any particular point on the body is smaller. Hence, less serious injuries will occur, this will also help to save the driver's and passenger's life. This is how a simple chemical equation avoids the deaths of millions.
Physic's Experiment
Investigating safety on cars
Introduction
As cars became increasingly powerful and fast, rate of incidents increased exponentially and, usually more violent. This meant, over the years, a constant research and development of new security measures, and even nowadays more and more new systems are introduced every day. This development gave birth to what we now consider to be the basic requirements of any safe car, such as seat belts, air bags and crumple zones.
Crumple zones
The structures that in cars are commonly known as crumple zones are areas placed on the front and usually on the rear of a vehicle that are designed to absorb energy during impact in a predictable and controlled way.
In the late 1950s, the general population still believed that the stronger the structure of a car, the safer that car would be during an incident. Actually, however, this kind of construction criteria proved to be fatal to most passengers. This is because during a collision all the energy of the impact went directly to the vehicle and onto the passengers. In 1967, the Mercedes Heckflosse was the first mass production car in the world to feature "crumple zones" and a safety cage. In order to fit appropriate crumple zones, the truck was made almost 50% bigger. Nowadays car featuring crumple zones and rigid cabs are standard safety requirements in almost every car made throughout the world. The fact that a car that crushes more easily protects its passengers more than a car that does not crush at all, may seem strange, but, in fact, the reason for this seem obvious when considering the physics behind it.
Newton's first law states that a body will remain at rest or continue travelling at uniform motion (constant velocity) unless a force is acted on it. Therefore, in a situation in which a car is impacting with a wall, if a vehicle is travelling at 70 km/h, the passengers inside are doing the same, and when the vehicle collides with the wall and comes to a sudden stop, the passengers' bodies will continue going in the same direction at the same speed, 70 km/h. As stated in the law, these bodies will keep on moving forward until they themselves collide with a part of the car or with another passenger. Even when the human body comes to rest in this kind of incident, its internal organs slam against each other and against bones. This will, of course cause, injuries to the passengers and sometimes even death.
Newton's second law of motion states that:
The law conveys that as the time taken by the car to arrive to complete rest increases, the force transferred to the car and, therefore its passengers, will be decreased. On the other hand, if the amount of time to reach complete halt is decreased, the force experienced will be greater.
Crumple zones are specifically designed in order to crush, absorbing part of the force of the collision. The force of the collision is given out during the impact in the form of heat, sound and in from of mechanical work done on the crumple zone. The front (and rear) part of the car acts as a cushion and it is able to increase the time taken to reach complete halt and, hopefully, save the passengers' lives. However crumple zones only work provided there is no intrusion on external elements, like the engine, in the rigid cage.
This concept can be easily explained thought a simply example. Take for instance two object, the first is a solid steel block, while the second is an aluminium can.
When the solid steel block (or car with no crumple zones) impacts with the wall, the wall does not move and, instead, exerts an equal magnitude and opposite direction force on the block. This causes the block to bounce off the wall in an elastic manner, conserving almost all its initial kinetic energy (EK) and, therefore, experiencing a large force.
On the other hand when considering the aluminium can, the situation is different. When an aluminium can (or a car with crumple zones) impacts with a wall, it does not conserve all of its initial kinetic energy (EK). This is because, instead of just bouncing off, some of the kinetic energy is transformed into mechanical work, heat and sound , during the squashing of the crumple zones. The result is a smaller force acted on the can. The action of crumple zones increases the time of collision and lessens the amount of force experienced by the aluminium can.
Specific materials
As seen in the previous section, the material with which different parts of the vehicle are built are of primary importance. Depending on how we want specific parts of the car to behave, specific material must be chosen. For instance, crumple zones are expected to crush easily, while the inner rigid cage is supposed to withstand higher forces without braking. Based on this information we can determine that the best material to build a crumple zone is an easily bendable metal like aluminium, instead for the rigid cage, a much harder alloy like steel.
Alloys are partial or complete solid solutions of one or more elements (metallic or/and non-metallic) in a metallic lattice. Alloys usually present different properties from those of the elements composing them. Alloying one metal with one or more metals or non-metals often improves the properties of the starting elements. For instance, when considering steel we can see how this alloy is stronger than its primary element, iron (Fe). Even though physical properties, such as density, reactivity, electrical and thermal conductivity, of the alloy does not differ inn great amount from those of its constituent elements, engineering properties such as tensile strength and shear strength can differ considerably. The tensile strength of a material is the maximum amount of tensile stress (measured in Newton) that it can tolerate before it tears to parts. The shear strength, instead, is the ability of the material to resist shear stress. The increase in both tensile strength and shear strength are usually due to the sizes of the atoms in the alloy. Larger atoms in the alloy apply a compressional stress on neighbouring atoms, and smaller atoms apply a tensional stress on their neighbours. This particular composition of alloys helps to resist deformation when a strong force is applied on it. Even when the amounts of each element in an alloy are altered slightly, this presents huge differences in physical engineering properties and behaviour. For instance, very small amounts of carbon (C) (between 0.2% and 2.1%) are added to iron (Fe) and act as hardening agents preventing dislocation of the iron atoms. From the image on the left it is possible to see how the atoms of carbon (A) place in between the atoms of iron (B), preventing the sliding of the layers of iron atoms. However, in case the amount of carbon was excessive, this would have the opposite effect, causing the iron to be brittle and break easily. Some alloys are made by melting and mixing two or more metallic elements. The first alloy ever discovered was bronze, it was made of copper and tin, and was discovered during the prehistoric period known as the bronze age. It was originally used to make tools and weapons, but later it has been used for ornaments, bells, statues, and bearings.
Video of crash tests
Investigating the effectiveness on crumple zones during a frontal collision
SUV
Mass of the trolley/kg
Distance from the wall /m
Time taken/s
Distance travelled after collision/m
2.79
0.97
1.31
0.17
2.79
0.97
1.15
0.10
2.79
0.97
1.38
0.08
Station wagon
Mass of the trolley/kg
Distance from the wall/m
Time taken/s
Distance travelled after collision/m
2.09
0.97
1.00
0.10
2.09
0.97
1.06
0.24
2.09
0.97
1.37
0.16
Supercar
Mass of the trolley/kg
Distance from the wall/m
Time taken/s
Distance travelled after collision/m
1.89
0.97
1.09
0.20
1.89
0.97
0.87
0.17
1.89
0.97
0.97
0.23
Calculations
V=d/t
a=(v-u)/t
F=ma
p=mv
SUV
Velocity/
ms-1
Acceleration/
ms-2
Force/N
Momentum
Time of collision/s
0.74
0.57
1.58
2.07
0.84
0.73
2.05
2.35
0.70
0.51
1.42
1.96
Station wagon
Velocity/
ms-1
Acceleration/
ms-2
Force/N
Momentum
Time of collision/s
0.97
0.97
2.03
2.03
0.92
0.86
1.80
1.91
0.71
0.52
1.08
1.48
Supercar
Velocity/
ms-1
Acceleration/
ms-2
Force/N
Momentum
Time of collision/s
0.98
0.82
1.54
1.68
1.11
1.28
2.42
2.11
1.00
1.03
1.95
1.89
Detailed history of the airbag production
Invented at the start of the 1950s, it only came to wide use during the 1960s. Air bag-equipped cars have demonstrated, both in controlled tests and everyday use, their effectiveness and reliability (in frontal collisions, deaths for drivers, were lowered by 28 percent in vehicles featuring air bags).
In order to answer to the increased of safety concerns of the consumers, the federal government has forced all car manufacturers to upgrade the safety features installed on their cars. The Department of Transportation (DOT) regulations require that all cars sold in the US, being produced starting from year 1990, had to feature a passive restraint system. Passive restraint systems are security systems that require no activation by the driver and usually are identified to be automatic seat belts and air bags. For air bags, until year 1994 the regulations only require a driver's air bag and must include passive protection on the passenger's side (seatbelts). Later, in 1991, a new law required both driver and passenger air bags in all cars by year 1998 and in light trucks and vans by year 1999.
Air bags are inflatable cushions designed to protect car passengers from serious or even fatal injury in case of a collision. The air bag is part of a system, also known as an air cushion restraint system (ACRS) or an air bag supplemental restraint system (SRS) (they are called supplemental because the air bag is designed to supplement the protection of seat belts). When detecting a collision, the air bags inflate instantly to provide the passenger with a big gas-filled cushion.
A typical air bag system consists of an air bag module (containing an inflator or gas generator and an air bag), crash sensors, a diagnostic monitoring unit, a steering wheel connecting coil, and an indicator lamp. These components are all interconnected by a wiring harness and powered by the vehicle's battery.
Air bag sensors are specifically designed to prevent the air bag from inflating when the car travels over a bump or in case of a minor collision.
In a frontal impact equivalent to hitting a solid barrier at a speed of 14.5 Km/h, the sensors located in the front of the car detect the sudden deceleration and send an electrical signal activating an initiator. The initiator is similar to a light bulb and contains a thin wire that heats up, breaking through the propellant chamber. This sudden penetration causes the solid chemical propellant, usually sodium azide, sealed up inside the inflator to undergo a very quick chemical reaction. This controlled reaction produces harmless blasts of the nitrogen gas that inflates the air bag.
The resulting nitrogen gas fills the nylon bag in less than one-twenty-fifth (1/25) of a second, opening its plastic cover on the stirring wheel and inflating in front of the passenger before this hits the stirring wheel. As the occupant hits the inflated bag, the nitrogen gas is pushed out through some openings at the back of the bag. The bag remains fully inflated for no longer than one-tenth (1/10) of a second and is almost completely deflated by three-tenths (3/10) of a second after the impact with the passenger. Talcum powder or corn starch is used to line the inside of the air bag and is released from the air bag as it is opened causing the characteristic white cloud.
Components of an airbag
An air bag is formed by three main parts: the nylon bag, the inflator, and the propellant. The bag is made from a woven nylon fabric and can differ in shape and size depending on the specific vehicle safety requirements. Talcum powder or corn starch is used when handling the air bag, since either of the two substances prevents the woven nylon fabric from sticking together and makes assembling process easier.
The inflator body is made from either stamped stainless steel or cast aluminium. Inside the inflator body there is a filter assembly formed by a stainless steel wire mesh with ceramic material held in between. When the inflator body is assembled in the factory, the filter assembly is wrapped by a metal foil to maintain the filter sealed preventing propellant contamination.
The propellant, typically sodium azide ,in the form of black pellets, is combined with an oxidizer and is usually located inside the inflator body between the filter assembly and the initiator.
Evaluation
While analysing how I dealt with the Group Four Project, I noticed some facts that I could have improved, hence improvements that could be done in how my Group Four has worked. The members of my Group Four Project were: Jacopo Mauro, Daniel Gardin, Maria Airchinsky, Edoardo Nalon and Laure Rasscheart. I noticed that when we started to work at the project, we weren't working as a team, as we still didn't know what we really had to do, as time passed we got to know each other better and gained more confidence, thus, we started to work more as a team and we managed to assign tasks inside within the group, for example: Edoardo had to contact some car stores and to gather information about the crumple zones and the materials used in the car production, Jacopo and Daniel were the ones who worked on the physics experiment, since they are the two members of the group who have taken the physics course, while Laure, Maria and I did the chemistry experiment, since we had the idea of the inflation of a balloon as a representation of an airbag.
The project could have been done in a more efficient way; we lost a lot of time to actually start with various ideas, set the experiments, and start working as a group, although it is possible to recognize the fact that our problems in getting organized were also due the fact that the members of the group never had study periods at the same time. Probably, something that could have really helped our report was to have a "leader" perhaps not the smartest, but the one who could have made sure that everyone who was actually proceeding with their tasks, and not wait for the last minute to do so. Perhaps he/she could have given the others some deadlines, and set up meetings to see how everyone was doing.
Another thing that we could have improved in our Group 4 Project was that we didn't have many meetings, we had also the summer to work on it, and we didn't really do much, so we waited for September when we came back from vacations to start again to worry about finishing the project.
Moreover, every member of the group was at a different level in chemistry and math, for example: Jacopo and Daniel are very good at chemistry and physics, in fact they chose the scientific course, while Laure, Edoardo, Maria and I don't even take physics and aren't objectively very good in chemistry.
However, what emerged from our difficulties was a complex and elaborated project, a research on an important thematic such as safety in the streets, focusing on car accidents. Our project could be expanded on an international scale by suggesting other schools to perform the same research as we did, hence rising internationally the awareness in students on how chemistry and physics are important on a daily basis, how these subjects are at the base of our most important healthy issues.
Edoardo Nalon Group Four Project 10.10.10
Edoardo Nalon Group Four Project 10.10.10
