Safety and Cars

Special Investigation 11 – Safety Devices

People using motor vehicles, bicycles or motorbikes use a number of safety device to improve their chances of survival in the event of an accident. Such devices are designed to either make an accident less likely to happen or to reduce the risk of injury or de ath id one does occur. Safety devices are now fitted as standard equipment on many motor vehicles and pushbikes. By far the most valuable and effective safety device for motor cars is the seat belt.

 Make a list of different types of safety devices used in or available for use in:

a) Motor Cars: Brakes, seatbelt, windshield, front lights, rear lights, doors, horn, air bags, child lock, mud flaps, sun visors, external sun visors, windscreen washer, windscreen wipers, windscreen demisters, external mirrors, weather shields
b) Motorbikes: Brakes, helmet, front lights, handle bars, rear lights, gloves, motorbike suits/protective clothing, cushion/seat
c) Pushbikes: Brakes, helmet, bike lights, handle bars, gloves, safety wheels, reflective lights, bell, cushion/seat

Examine the seat belt in a car. How do seat belts alleviate or eliminate the usual tragic results of accidents? How do seatbelts work? What are they made of and why? What types are available? What is the best type and why? Comment on the effectiveness of seat belts. Estimate the average force involved in a particular collision with and without a seat belt

Seat belts hold the passenger in place and prevent them from moving forward or flying out of their seat during a collision or a sudden stop. This prevents any passenger from flying into the windshield, windows or the seats in front of them. It reduces the force as it absorbs the majority of the force and spreads it. Seatbelts use a retractor mechanism that works on the idea of a wound seatbelt on a spool. This spool has attached a spring that pulls the seatbelt taut and therefore ensuring the safety of the seatbelt. By pulling the seatbelt “out” you are ultimately putting tension on the spring as you are winding it in an opposite direction; unwinding it. This increases the tautness of the belt and increases the safety. When a large impact/force is applied to the belt the lock system is activated. This system is what keeps you in place. When the spool spins, its jagged edges catch on to a mechanism underneath.

Repeat as much as you can of step 2 for at least three other safety devices, e.g. helmets, child safety seat, booster cushions, head rests, protective clothing, roll bars

Helmets: Helmets are a barrier between the person and the point of impact. It absorbs most of the force of the impact and spreads it around the head too, reducing the force and chance of injury. Also, being a solid object, it reduces the chance of something penetrating through, preventing the wearer from getting their head scratched by external objects. The helmet usually is made of a plastic and may have padding or a soft, impact- absorbent material that will enhance the impact-absorbing of helmet. They are usually light-weight and generally of low volume to further reduce the chance of injury; generally high-volume and heavier helmets don’t protect the wearers head as well, making them counter-productive.

Child Safety Seat: It is a special seat that is attached/placed on usually the centre back seat of a car. This seat is secured through the seat belt already in the car or other safety harnesses depending on the car. The safety seat has a harness rather than a belt that hold the child better due to their size. Typically those in a child safety seat are small and would easily slide out or would not be able to harness the full potential of a normal seatbelt due mainly to their size. The child could also easily release the seatbelt at any time which would be dangerous both for the child and the driver. The harness crosses over the child and is seemingly very difficult for the child to fly out or escape without a parent to aid.  Typically, a child safety seat will also be made of soft padded material such as cotton or stuffing that absorbs the impact whilst cushioning the child during a crash or bumps on roads. The material may also be encased or embodied with a plastic or metal shell that further absorbs the impact for reaching the child while keeping the seat steady and stable.

Protective Clothing: Protective clothing is worn usually to prevent scratches and cuts rather than to reduce impacts like the other safety devices explained above. Protective clothing is usually made of tough material that is scratch-resistant or can withstand heavy amounts of wear and tear, such as leather. Protective clothing, due to them being of a high-density and made of thick fibres, prevents external objects from cutting or scratching the wearers skin. External objects cannot penetrate the thick material and thus it keeps the wearer from acquiring any injures or scratches.

Why do we need minimum standards for safety devices?

Minimum standards allow the government or officials to carefully examine and make sure that all citizens are safe. The minimum standards prevent companies from making dodgy or unsafe devices. It sets a bar for all devices to be made and is set based upon tests and research. Without such standards, many companies, to earn a larger profit, would use cheaper materials or would cut back on certain aspects by not including them or making them of low quality. The standards therefore, make sure the consumers are safe at all times and that they know that all devices in their car are at the minimum to prevent an injury or death or damage of any sort.

How do the following devices improve the comfort and safety of travel? – windscreen washers, windscreen demisters, external mirrors, weather shields, external sun visors, mud flaps, reversing lights.

Windscreen washers: They keep the windscreen of the car clean as rain, insects, dirt and excretions and other material build up on the car. It is used in conjunction with windscreen wipers and allows the driver to quickly wash off the material from the windscreen to allow for clean view of the road. Not only does it make it safer for the driver, who will be able to see the road and other cars better, but will also allow for a more comfortable ride as the passengers will be able to see the road and the scenery clearer.

Windscreen demisters: These stop the windscreen from fogging up and becoming moist. If there is a great temperature difference between the car and the outside, typically when the car is warmer than its surrounding environment, and when the humidity is high within the car, the water vapour in the air will condense on the cold windscreen. The demisters warm up the windscreen whilst preventing the window from accumulating water vapour. Without it, the window would fog up and driver would not be able to see and could crash or cause and accident.

External mirrors: Since cars are not entirely see-through and are not made completely out of glass, it is hard to see certain areas around the car. External mirrors allow the driver to easily spot a car coming up alongside without needing to turn and look backwards or miss it because it is in a blind spot or a spot not visible by just turning oneself. The driver can quickly spot the car and know when to turn or if it’s safe to move into another lane.

Weather shields: It allows the passengers of the car to wind down the window of car without getting wet from the rain or heavy amounts of wind that would be present. The weather shield is a barrier in this instance. It not only allows the passengers to take a breath of air but also prevents harsh wind and rain from getting into the car.

External sun visors: These sun visors reduce glare and large amounts of sunlight that can hinder a driver’s sight, causing a crash or an accident. It allows the drivers to see better and provides them with a bit of shade. The visors also make the journey pleasant for all passengers as it stop the glare from the sun and reduces the brightness that would be shone on the faces of the passengers.

Mud flaps: It prevents dirt and objects from hitting the car and passengers when the wheels of the car are moving. The high speed of the rotation of the wheels can cause mud and objects to fly out which is dangerous. The mud flaps prevent such occurances from happening. A flying object could seriously hurt a passenger or individual. The flaps also prevent mud and objects from flying into the motor and the important mechanical parts of the car. Mud can dry into almost a solid and this can prevent certain parts of the car from working or could damage the vehicle without warning to the driver, which would make it dangerous for all occupants of the car. Mudflaps prevent this from happening. It also keeps the car clean which not only reduces a hassle but gives the passengers and drivers peace of mind whilst on a trip.

Reversing lights: Reversing lights indicate to other drivers that the car is reversing and prevents drivers from being unaware or surprised when the car in front is moving backwards. This increases safety as there will be an indication of the cars movement and prevents cars from collision or accidents that could otherwise be prevented.

Special Investigation 13 – Energy Changes and Cars
A car is an energy-converting device. In a car engine the chemical energy of the fuel is changed into heat energy. This causes movement (kinetic energy) of the pistons and other parts of the car’s transmission. This kinetic energy can be used to overcome friction between the car’s tyres and the road surface. The car also produces sound energy.

Imagine a car travelling along a highway in the country. The driver falls asleep whilst driving and the car turns off the road and hits a large tree head-on. The car is badly damaged and the engine is pushed back into the passenger compartment. The driver survives and is held inside the car by a seat belt.

 List all the energy changes that occurred from the moment the car left the road

Chemical energy (from fuel combustion) > Mechanical Energy (produced by the wheels and the mechanisms of the car) > Kinetic energy (attained from the mechanical energy as the car continuously moves forward) > Sound energy (large crash sound is made) > Heat energy (sound energy causes particles to move whilst also causing heat to be produced/ The car hits the tree causing particles to vibrate)

What would have happened if the driver had not been wearing a seat belt? Why?

The driver would have continued moving in the same direction the car was moving in and the same speed before the car hit the tree. He would fly forward into the windscreen and may fly out into the tree if the car was travelling too fast. This is because there is nothing preventing him from staying within the car and thus the law of inertia is brought up. It states that an object will continue moving in the same direction or will remain at a constant or balanced state unless acted upon by an external force. Putting this back into the scenario and the driver would therefore continue flying forward as he still has the force of the car pushing him forward before the car hit the tree and therefore, he will continue flying forward.

Discuss the laws of physics that are involved in such a collision

The law of inertia is in play in this scenario. The driver will continue moving in the same direction and speed of the car even when the car stops until he is prevented or slowed by another object. The second law that concerns the size of a force is also in play. Depending on how fast the car was moving and how much the cars mass was, the rate of velocity and the amount of impact that will be present when the car can be calculated and seen. A greater force means a bigger impact and higher chance of death or injury. The force of the impact will also determine the damage the car will endure as well as the tree. Finally the 3^rd law of physics is also present; that each force will have an equal or opposite reaction. As the car slams into the tree the reaction force is present and causes the car to stop.

If you are involved in a collision with a large tree are you better off being in a large car or small car? Discuss.

A larger car would be able to absorb more of the impact and spread it over a greater area as it is larger compared to a smaller car.  The impact would therefore not be concentrated in one point or a small area and would spread out, reducing the force of the impact. There would also be more material between the sides of the car as it is larger which could reduce the impact as the force could be absorbed or spread out. However, as it is a larger vehicle the force could be greater. The second law of physics states that F=Ma (force is equal to mass multiplied by acceleration) and therefore because the smaller car would be of less mass the force of the impact would be significantly less than that of a bigger vehicle.

List the energy changes that are occurring whilst a car is being driven along a road.

Chemical Energy (From the combustion of the fuel within the car) > Mechanical Energy (pistons and relative parts of the car are moved) > Kinetic energy (The car is pushed forward and is opposing the friction of the wheels and the ground) > Sound energy (The resistance to friction can be heard; the sounds the piston makes whilst moving) > Heat energy (Heat is produced from the combustion chambers and from the tyres going against friction)

B

Modern highways and freeways contain a number of safety features like protective barriers that help reduce the severity of an impact by a car. Such features are designed to slow down the loss of energy in a single car collision. (Damage is greatest when the loss of energy is rapid).

 List various features positioned along highways and freeways that help reduce the loss of energy during impacts. What are these features made of and how do they work? Take photographs or make sketches of such features. You may have to look before answering this question. Make a one page report of your findings.

Fitch Barrier: This barrier absorbs the impact of the car during a collision. It is a sand or water filled barrel that is able to disperse the force of the impact whilst having a low resistance force so that the driver has a less chance of damage or injury. They create a cushion for the car. This allows for the car to slowly come to a stop and thus reduces the risk of injury to the passengers of the vehicle. Often they are brightly coloured and are situated in between the exit ramp and the main freeway, in a triangular position so that the most kinetic energy can be dissipated.

Impact attenuator: This device reduces the damage to vehicles during a collision. The device is made of a crushable metallic material that will crumple and fold when smashed into, absorbing and spreading the force of the impact. They are usually positioned near traffic barriers and may have stripes or indicative signs to warn drivers.

Guard Rails: This metal rails are situated on the sides of some freeways and highways and are used to indicate or to slow down cars. They are made of strong metallic materials and often are situated on wooden or metal bars or beams. The device absorbs the impact of the car and through friction; it slows the car down making it come to a stop. The bars keep the cars on the road and by slowing the car down, reducing the loss of energy and spread it out over time.

Median Strip: This concrete barrier lies in the centre on the highway and separates the two flows of traffic. When a car collides with this, the force is absorbed and spread through the strip, minimising the force of the impact. This barrier prevents any car from crossing over to the other flow of traffic. Often these barriers can move slightly or are anchored to the ground in such a way that the force flows down and into the ground instead of back towards the driver.

Grassy Plains: Often on the side of freeways or highways, there are grassy plains or rough terrain present. This rough terrain will increase the friction between the wheels of the car and the ground and will slow the force of the car down, even before an impact. Sometimes they are on an upward slope or a curvature which causes the vehicle that has run off the main road to work against the forces of gravity, in addition to the increased friction, thus slowing the vehicle down and reducing the force behind the car.

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