# Force and Linear Motion in Car Accidents

3402 words (14 pages) Essay in Physics

18/05/20 Physics Reference this

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Claim

Every k over the speed limit is a killer.

Rational

Familiarity of forces and motion has led to growths in developments that have reduced the risks for drivers, their passengers, and additional road users for instance cyclists and pedestrians. Car safety has been enhanced through the development and utilization of devices such as seatbelts, crumple zones and airbags (McGraw-Hill;2019.). A knowledgeable understanding of motion has also led to the design and implementation of traffic-calming devices such as speed bumps and safety barriers (McGraw-Hill; 2007.). Knowledge of force and linear motion is utilized in forensic and scientific investigations into car accidents. Road laws and regulations, as well as the setting of speed limits in specific settings, are built on these forensic investigations and have brung about fewer road accident injuries and fatalities. Newton’s Three Laws of Motion explain how forces create motion in cars. These laws are usually referred to as the Laws of Inertia, Acceleration, and Reaction (McGraw-Hill; 2007.) (McGraw-Hill;2019.)

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The First Law of Motion means that objects that have greater momentum also have greater inertia (McGraw-Hill; 2007).  A stationary object will require a push or a pull to set it in motion. When the net force on an object is zero, its speed and direction of motion will remain unchanged (McGraw-Hill; 2007). This is true for equally stationary objects in addition to those already in motion. An object in motion, and has no other force acting upon it, for instance the force of friction, will remain in continuous motion (McGraw-Hill;2019). A person travelling in a car at 60 km/h will keep in motion at the same rapidity if the car stops abruptly. This indicates that they will be thrown headlong and can injure themselves striking the steering wheel or windscreen (McGraw-Hill;2019). We use seatbelts to fasten ourselves to the moving car combating the Law of Inertia. The seatbelt permits us to become one with the the car, so that when it decelerates, we slow down with it (McGraw-Hill;2019). The Law of Inertia also demonstrates to us that loose objects in a car luggage, sharp tools or pets can also be hazardous when a vehicle has to stop suddenly (McGraw-Hill;2019). Once a stationary car is hit from behind it can be unexpectedly pushed forward. Inertia causes the car to be in motion though the passengers head remains stationary, initiating whiplash. Tailored head rests are now obligatory in cars in order to decrease injury by whiplash subsequently rear end collisions (McGraw-Hill;2019).

force,

$\mathbit{m}$

mass and

acceleration.

Newton’s second law supports our consciousness of road safety by showing us that the magnitude of the net force on a vehicle is the product of its mass and acceleration (McGraw-Hill;2019). When there is a general force on an object that is not equally balanced, the object accelerates in the direction of the overall net force (McGraw-Hill;2019). Acceleration can be negative, such as when a driver hits the brakes and increases the force of resistance to slow down the vehicle (McGraw-Hill; 2007). Here, a rapid increase in force consequences in a rapid negative acceleration. A larger force is needed to accelerate an object with a greater mass, subsequently trucks take longer to accelerate to the speed limit than cars (Fletcher, N. 2015). The formula used to calculate braking distance can be derived from the general equation:

${{\mathbit{V}}}_{{\mathbit{f}}}^{{\mathbit{2}}}\mathbit{=}{\mathbit{V}}_{\mathbit{0}}^{\mathbit{2}}\mathbit{–}\mathbit{2}\mathbit{ad}$

Where

${{\mathbit{V}}}_{{\mathbit{f}}}$

is the final velocity,

${{\mathbit{V}}}_{{\mathbit{0}}}$

is the initial velocity,

${\mathbit{a}}$

is the rate of deceleration and

${\mathbit{d}}$

is the distance travelled during deceleration.

The Law of action and reaction for every action there is an equal and opposite reaction (Fletcher, N. 2015). If you push in contradiction of an immobile object, the object pushes back equally. When the push on the object is superior than the of the push it can return, it will be inmotion. When equally two indistinguishable vehicles hit each other with equal momentum the impairment to both will be equal. But when one vehicle has bigger mass and a greater motion (is heavier and faster), it will employ a greater force (Fletcher, N. 2015). If you crash a light wieght object with a heavier object, the lighter object rebounds more (Fletcher, N. 2015). This Third Law of Motion clarifies cars move forward instead of the road moving backward when you step on the accelerator (Fletcher, N. 2015). The force applied by the tyres on the road is harmonized by an equal and opposite force applied by the road on the tyres. If that force is sufficient to overcome the car’s inertia, of that on a clean, dry road, the car accelerates forward (Fletcher, N. 2015). Heavy vehicles with higher momentum are harder to stop than a lighter vehicle moving more gradually (Fletcher, N. 2015). Subsequently, the research question to be investigated is as follows:

‘How has advances on technology in the field of the laws of force and motion, allow improvements and developments in the performance of road safety through the reductions in the risks for road accident injuries and fatalities?’

Background

In the 1700’s, while trying to identify a single rule by which the motion of all bodies could be calculated, English mathematician and theoretical physicist Isaac Newton developed the Three Laws of Motion, changing the way we think about the world (Fletcher, N. 2015). They were published in 1686 in a work frequently been recognised by some to be the most significant scientific discovery in history and the foundation of which modern physics was constructed (Fletcher, N. 2015). We can use Newton’s Three Laws of Motion to help us recognize the physics of car crashes (Fletcher, N. 2015).

Evidence

Figure 1: The faster you go, the greater your risk of a crash

A driver notices a pedestrian crossing the road. If the car is travelling at 50 km/h and the driver brakes when the pedestrian is 29 meters away, there will be enough space in which to stop without hitting the pedestrian. Increase the vehicle speed by just 10 km/h and the situation changes dramatically. At 60 km/h, with the pedestrian 29 meters away and the driver braking at the same point, the car will be travelling at 44 km/h when it hits the pedestrian. The following diagrams (Figure 1 and 2) illustrates the stopping distances and impact forces at various speeds:

Figure 2: The greater your risk of a crash, the faster you go

Figure 2: Applying the Knowledge and Understanding of Physics to Reduce Road Accident Injuries and Fatalities.

Figure 2.1: Reaction time

In a 60 km/h zone, Car 1 is travelling at 65 km/h, and Car 2 is travelling at 60 km/h. A child on emerges from a driveway just as the two cars are side-by-side. The drivers both see the child at the same time, and both take 1.5 seconds (normal human reaction time) before they fully apply the brakes. In those few moments, Car 1 travels 27.1 metres and Car 2 travels 25.0 metres.

Figure 2.2: Stopping Time

The formula used to calculate braking distance can be derived from a general equation:

${{\mathbit{V}}}_{{\mathbit{f}}}^{{\mathbit{2}}}\mathbit{=}{\mathbit{V}}_{\mathbit{0}}^{\mathbit{2}}\mathbit{–}\mathbit{2}\mathbit{ad}$

Where

${{\mathbit{V}}}_{{\mathbit{f}}}$

is the final velocity,

${{\mathbit{V}}}_{{\mathbit{0}}}$

is the initial velocity,

is the rate of deceleration and

${\mathbit{d}}$

is the distance travelled during deceleration. Because we recognize that

${{\mathbit{V}}}_{{\mathbit{f}}}$

will be zero when the car is stationary, this equation can be re-written as:

From this we can see that braking distance is comparative to the square of the speed which means that it increases significantly as speed increases. If we assume that

${\mathbit{a}}$

is 10 metres per second per second and assume that the road is flat and the braking systems of the two cars are equally effective, we can now calculate braking distance for cars 1 and 2. For car 1,

metres, while for Car 2,

metres.

Adding reaction distance to braking distance, the stopping distance for Car 1 is:

metres.

For Car 2, stopping distance is:

metres.

Car 1 therefore takes 4.5 more metres to stop than Car 2, a 12% increase.

Figure 2.3: Impact

Thus, the impact occurs at about 30 k/h, undoubtedly, fast enough to kill the child. If the car’s initial speed was 70 kilometres/hour, the impact velocity would be 45 kilometres/hour, more than enough fast enough to kill.

Quality of evidence

The statement, “in more than 50 decades of civil nuclear power experience nuclear wastes have not caused any serious health or environmental problems nor posed any real risks to people. There has been no pollution or plausible hazard from such material routinely removed from power stations…” was made by the World Nuclear Association in 2017. It is suggested that teh second source confirming this would be required to remove claims of bias, and to have greater confidence in the accuracy of the statement. A lot of the information about forces and motion has led to growths in developments that have reduced the risks for drivers’was sourced from ‘The Road Safety Total Learning Resources’ (https://www.mynrma.com.au/-/media/documents/motoring-education/study-guides/nrma-the-road-safety-total-learning-resource-years-9-10.pdf?la=en) . Whilst there is no indication that Tokamak Energy company is negligent, dishonest or biased, it would be essential that furthermore sources confirm the information gathered in the evidence. Understandably, evidence such as this is likely to be commercially sensitive, making it publicly available may threaten their business opportunities. As such, it is suggested that advances on technology in the field of the laws of force and motion, have improved the performance of road safety through the reductions in the risks of injuries and fatalities

Evaluation of claim

The research question, “How has advances on technology in the field of the laws of force and motion, allow improvements and developments in the performance of road safety through the reductions in the risks for road accident injuries and fatalities” was addressed by gathering evidence. The evidence suggests that the laws of force and motion have improved the performance of road safety in reducing risks of road accident injuries and fatalities. Though, further data is required to establish an even more solidified conclusion to the evidence suggested in the claim, the findings of this investigation, if applied to the claim, suggest that the claim is supported with the evidence gathered in this investigation.

Improvements to the investigation

In order to address the limitations of the evidence identified previously, some improvements could be made. The first improvement would be to research how many people die each year because of road accidents and how intoxicated drivers contribute to higher car accident injuries and fatalities. It would be important to establish these to suggest that advances on technology in the field of the laws of force and motion, allow improvements and developments in the performance of road safety through the reductions in the risks for road accident injuries and fatalities.

Extensions to the investigation

Extensions to the investigation It is recognised that the research question used to direct this investigation focussed on one aspect of the claim. An aspect of the claim that Knowledge of the laws of motion can reduce the car accident injuries and fatalities was directly considered in this research. Furthermore, research could be considered when investigating further aspects of the claim; research could be conducted to estimate the damages it costs, how many people die each year on average and how drink driving contributes to higher car accident injuries and fatalities. Research into these processes involved in car accident injuries and fatalities should be conducted. This will help establish the likelihood of achieving a more solidified conclusion.

Conclusion

It can be seen that enough evidence has been gathered to establish laws of force and motion, allow improvements and developments in the performance of road safety through the reductions in the risks for road accident injuries and fatalities. The evidence found in the claim “Every k over the speed limit is a killer.” can be supported by this research congregated.

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