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Physics – Module 1 – Moving About 1. Vehicles do not typically travel at a constant speed

• identify that a typical journey involves speed changes A typical journey will involve speed changes. This may be slowing down due to getting caught in traffic, speeding up while going downhill, slowing down while turning etc.

• distinguish between the instantaneous and average speed of vehicles and other bodies

The instantaneous speed of any object is the speed at that particular instant of time. Eg. During a 100m race this may be at the 50m point. (Which may be 18.5 m/s) The average speed of any object is the speed over a period of time, or a distance. Eg. During a 100m race the average speed of the runner from the starting point to the 50m point may be 10m/s. The average speed is the total distance traveled divided by the total time taken, whereas the instantaneous speed is just a particular point in time (no other considerations are take such as how far traveled previously).

• distinguish between scalar and vector quantities in equations There is one main difference between scalar and vector quantities. That is that scalar quantities do not give the direction in which the object is moving, the only give the magnitude. Vector quantities give both direction and magnitude. Eg. 100m/s – Scalar since there is no direction given (In this case this was speed) 100m/s North East – Vector since there is a direction given (This was Velocity) Examples of Scalar and Vector quantities: Speed - Scalar Velocity - Vector Volume - Scalar Acceleration - Vector Distance - Scalar Displacement - Vector Time – Scalar Force – Vector Distance is the total length travelled by an object from start to stop. It is a scalar quantity. Displacement is the direct distance from an objects start to stop. It is a vector quantity.

Distance

Displacement

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• compare instantaneous and average speed with instantaneous and average velocity

Instantaneous speed is the speed of an object at any particular point in time. Average speed is the distance traveled during a particular period of time divided by the time itself. Instantaneous and average speeds are both scalar quantities. Velocity is a measure of the time rate of displacement. It is a vector quantity. The instantaneous velocity is the velocity (speed and direction) of an object at a particular point in time. The average velocity is the total displacement of that object divided by the time period. For motion in a straight line, the magnitude of the velocity is the same as that for speed.

• define average velocity as: “r” refers to the total displacement. ‘t’ refers to the total time. This equation is used to finds the average velocity and is the total displacement divided by the time. Example question: If a cyclist rides a distance of 6km north and then 8km east in 20 minutes. Determine: a) Distance traveled b) Displacement c) Average speed 8km d) Average Velocity Answers: a) Distance = 6+8 = 14km b) Displacement using Pythagoras’ theorem: 10km Direction is given by tan x = 8/6 6km x = 53.1 degrees x Displacement Therefore Displacement is 10km north 53.1 degrees East c) Average Speed = Distance traveled / Time taken: = 14km / 20 minutes = 0.7 km/m d) Average Velocity = Total Displacement / Time: = 10km North 53.1 degrees East / 20 minutes = 0.5 km/m North 53.1 degrees East.

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• Present information graphically of: o Displacement vs. time o Velocity vs. time o For objects with uniform and non-uniform linear velocity

Displacement-Time “The gradient of a displacement-time graph represents the velocity”

Velocity-Time “The gradient of a velocity-time graph represents acceleration”

“ The displacement of an object during a time interval can be determined by obtaining the area under the graph”

Acceleration-Time

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2. An analysis of the external forces on vehicles helps to understand the effects of acceleration and deceleration

• describe the motion of one body relative to another When the velocity of an object is measured by a moving observer it is referred to as the ‘Relative Velocity’. The equation to the left states that the Velocity of A (object) relative to B (Observer) . Is the velocity of A minus the Velocity of B.

For Example: If you are in car travelling at a constant velocity of 90km/h due west on a straight road, and there is a car ahead of you travelling at 100 km/h due west. Then the relative velocity of that Car:

Relative Velocity = 100 – 90 = 10 km/h due west. For Example: If you are in car travelling at a constant velocity of 90km/h due west on a straight road, and there is a car ahead of you travelling at 100 km/h due east. Then the relative velocity of that Car:

Relative Velocity = -100 – 90 = -190 km/h due west = 190 km/h due east

• identify the usefulness of using vector diagrams to assist solving

problems Vector diagrams are useful when trying to solve problems in which objects are moving in different directions. As was seen in the cyclist problem, the use of the Vector diagram allowed us to clearly depict the situation and made solving the problem clearer and simpler. eg. Find V1/2 = V1 - V2 V1/2 = V1 - V2 = V1 + (-V2)

Note: To subtract Vector 2 from Vector 1. Then Add Vector –2 to Vector 1 (In-Diagram)

V1

V2

V1

V2

V1 - 2

baba VVV

!!!−=

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• explain the need for a net external force to act in order to change the velocity of an object

Newton’s First Law: “An object will stay at rest or travel at a constant velocity unless acted upon by an external unbalanced force.” Newtons First Law relates to a concept called Inertia. Inertia is the tendency of an object to resist a change in motion. Inertia is not a force; it is a property of all objects. The inertia of an object depends only on its mass. For example, a larger object travelling at a high speed is harder to stop than a lighter object travelling at the same speed. This means that in order to change the velocity of an object you need an external unbalanced net force. The vector sum of the forces acting on an object is called the net force. For example when a car accelerates, the thrust provided by the engine allows to car to overcome the friction applied to it and allows it to change its velocity. It is difficult to see the law applied on Earth as there are always forces applied on the object on Earth, eg. Air resistance, friction, gravity etc. But in space where there is little external force this law holds true. Therefore, in a perfect vacuum, unless an object has a force applied on it, it will remain at rest or move in the same direction at the same speed.

• describe the actions that must be taken for a vehicle to change direction, speed up and slow down

In order to speed up, the thrust provided by the engine of the vehicle must exceed the friction that is being applied on the vehicle. I.e. It must have a overall net force in the forward direction. In order to slow down, the thrust provided by the engine of the vehicle must be less than that of the friction that is applied on the vehicle. This can be done by releasing foot off the accelerator which will result in the gradual slowing down of the vehicle or the brake can be applied which increases the amount of resistance (friction) between the vehicle and the ground, resulting in a more rapid deceleration. In order to change direction of a vehicle, a external unbalanced force must be applied from one side of the vehicle. Eg. When a car wants to turn right, the steering wheel is turned right which causes more force to be applied on the right side of the car resulting in the car to change direction to the right.

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• describe the typical effects of external forces on bodies including: § friction between surfaces § air resistance

Friction is the resistance (in terms of motion) between the surfaces of two objects. It decelerates that object. Air resistance acts in the opposite direction of motion to an object and also decelerates it. Gravity (Weight) is the force that pulls all bodies towards the ground. It has no obvious affect on most objects, but on objects that need to move upwards such as rockets, gravity poses as a significant resistance to them. Normal Reaction force is a force that acts perpendicular to a surface as a result of an object applying a force to the surface. For example when you walk, to exert force onto the ground and there is a normal reaction force which is exerted onto your foot. The magnitude of both forces is the same. Driving force (Thrust): The thrust is simply the forward force applied on a body which causes it to accelerate.

• define average acceleration as:

The rate at which an object changes its velocity is called its ACCELERATION. Acceleration is a Vector quantity. The ‘v’ refers to change in velocity. The change in velocity is equal to the ending velocity minus the initial velocity which gives us the second equation.

• define the terms mass and weight with reference to the effects of gravity

Your mass will not change if you change locations, no matter where you go. If you have 50kg of mass on the Earth. Your will have 50kg of mass on the Moon as well. It is your weight that will change.

W=mg

W refers to weight M refers to mass G refers to the force of gravity. (gravitational field strength) On Earth the force of gravity is approximately 9.8 N Therefore to determine your weight on Earth, you multiply your mass by the gravitational field strength (9.8).

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• outline the forces involved in causing a change in the velocity of a vehicle when:

§ coasting with no pressure on the accelerator § pressing on the accelerator § pressing on the brakes § passing over an icy patch on the road § climbing and descending hills § following a curve in the road

Coasting with no pressure on the accelerator: In theory if this was the case, you should move at a constant velocity eternally but on Earth this is not true as there are several resistance factors that cause the car to slow down and eventually come to rest. Air resistance and friction are the two major components. Friction between the tyres and the road as well as the air resistance on the vehicle cause it to eventually come to a halt. Thus the velocity is always decreasing. If the car was to move at a constant velocity, then the thrust provided by the engine should be equal to the resistance applied by the friction and the air resistance. This will result in a overall net force of 0 and thus you would coast along at a constant velocity. Pressing on the accelerator: This will result in a force to applied by the engine. The thrust applied by the engine will exceed the friction and air-resistance factors and cause the vehicle to increase it’s velocity accordingly (accelerating). Simply, when the accelerator is pressed a force is applied on the road by the wheels of the car, and due to Newton’s third law, we know that there will be an equal and opposite reaction force and this is the force that causes the vehicle to accelerate. Pressing on the brakes: When the brakes are pressed, the engine produces a force which causes the wheels to stop turning (or turn slower). This increases the frictional forces that are applied on the car as well as reduces the thrust that is applied by the engine. Due to both of these factors, the car’s velocity will reduce. Thus the care will decelerate (or accelerate in a negative direction). Passing over an icy patch on the road: Let us assume that the car is travelling at a constant velocity (i.e. no net force). An icy patch on the road will apply less friction onto the car than a normal bitumen-based road will. Due to this fact, as the car gets onto the icy patch and keeps the same pressure on the accelerator, it will travel faster (accelerate) as the frictional forces have been reduced, which means that there is a net force in the direction the car is travelling. This causes increases in velocity and causes the car to accelerate. Also, due to the fact that the icy road provides minimal friction to that of the normal road, it will be difficult for the vehicle to reduce it’s velocity. This is because as the brakes are applied, the deceleration of the car relies on the frictional forces between the wheels and the road and since there are minimal frictional forces, it will be hard to car to slow down.

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Climbing and Descending Hills:

It is important in these scenarios to split up the several forces into their components. In the diagram to the right. The angle of inclination is always equal to the angle of between the normal and the force of gravity. As can be seen there is a net force applied in the downhill direction. This force can be calculated if the mass of the object is known. The normal reaction force is always perpendicular to the surface and this can be seen in both scenarios. Friction and air resistance play important roles in restricting the movement of the object and the amount of force needed is dependant on if you are travelling uphill or down hill. In the diagram to the left, in order to accelerate the car, the driving force must be greater than the sum of the frictional force, air resistance and the downhill force (weight component parallel to surface) applied on the car. These three forces are acting in an opposite direction to the direction of the car. Thus this shows why more force is needed to travel uphill, rather than downhill. Following a curve in the road: When a vehicle must follow a curve in the road a different type of force is applied on it. It is called the centripetal force. The centripetal force is the net force on an object travelling in a circular path at a constant speed. The force is directed towards the center of the circle.

Σ F = mv2/ r M = mass of object V = Velocity R = Radius Example: A car of mass 1200kg drives along a roundabout at a constant speed of 15m/s around a curve with a radius of 12m. Calculate the net force Net force = (1200 x 15 x 15) / 12 = 2.25 x 104 N

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• interpret Newton’s Second Law of Motion and relate it to the equation:

Σ F = ma

M = mass, A = acceleration. Basically, the net force is equal to the mass multiplied by the acceleration. Newton’s Second Law of Motion: “The change in velocity (acceleration) with which an object moves is directly proportional to the magnitude of the force applied to the object and inversely proportional to the mass of the object.” Example: What is the magnitude of the net force acting on a 1600kg car when it’s acceleration is 2.0 m s-2 Force = 1600 x 2

= 3200 N (Force is always measured in Newtons – N) Newtons Second Law: It allows to determine many things such as;

- You are able to determine the net force, without knowing any of the individual forces acting on the object.

- Determine the mass of an object. - Predict the effect of a net force on the motion of on object of known mass.

• identify the net force in a wide variety of situations involving modes of transport and explain the consequences of the application of that net force in terms of Newton’s Second Law of Motion

In planes and cars and other vehicles, the net force is a very important consideration. For example in an A380 plane it was calculated that the plane needed a take off speed of 300 km/h. This was then used to determine the extent of force the engines needed to produce in order to make the plane take off in 35 seconds. F = m x a = 560 000 kg x ( 83.3 / 35 ) = 1 332 800 N This is just one of the many situations where Newton’s second law is applied to modes of transport.

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4. Change of momentum relates to the forces acting on the vehicle or the driver

• define momentum as: p = mv ‘p’ is the standard symbol for momentum ‘m’ stands for mass ‘v’ stands for velocity Momentum is a Vector quantity.

• define impulse as the product of force and time Impulse is the change in momentum. It is also known as the product of force and the time interval over which it acts. Impulse is a vector quantity with units – N s The formula for impulse is Impulse = Force x Time or I = Ft Change in momentum (impulse) can also be written as:

mΔ v = m(v-u) = mv – mu

= pf – pi where pf = final momentum of the object pi = initial momentum of the object NOTE: If a graph of force vs. time is plotted, the impulse can be calculated by determining the area under the graph.

• explain why momentum is conserved in collisions in terms of Newton’s Third Law of motion

Newtons Third Law: Whenever an object applies a force (an action) to a second object, the second object applies an equal and opposite force (called a reaction) to the first object. Law of conservation of Momentum: For a collision occurring between object 1 and object 2 in an isolated system, the total momentum of the two objects before the collision is equal to the total momentum of the two objects after the collision. That is, the momentum lost by object 1 is equal to the momentum gained by object 2.

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3. Moving vehicles have kinetic energy and energy transformations are an important aspect in understanding motion

• identify that a moving object possesses kinetic energy and that work done on that object can increase that energy

Energy can be defines as the capacity to do work. It is a scalar quantity.? Work is done when an object moves in the direction of a force applied to it. The amount of work done is the product of the magnitude of the force and the displacement of the object in the direction of the force. Work is a scalar quantity. Some characteristics of energy: - All matter possesses energy - Energy can take many different forms such as light, sound, thermal, kinetic,

gravitational potential, chemical, nuclear etc. - Energy can be stored, transferred to other matter, or transformed from one

form to another. Some transformations can be heard, seen, felt, smelt or tasted.

- It is possible to measure the quantity of energy transferred or transformed.

Energy can be transferred to or from matter in several different ways. Energy can transferred by:

- Emission or absorption of electromagnetic or nuclear radiation - Heating / cooling of an object or substance as a result of a temperance

difference - The action of a force on an object resulting in movement.

The transfer of energy by the action of a force is called mechanical energy transfer.

W = Fs

‘F’ is the magnitude of the force. ‘s’ is the displacement in the direction of the force.

The standard SI unit of work is a joule (J) Kinetic energy is the energy associated with the movement of an object. ‘m’ = mass ‘v’ = velocity Any moving object possesses kinetic energy, and work done on that moving object will increase the kinetic energy of that object. Note: the kinetic energy of a moving vehicle cannot be created – it must be transferred from another object or transformed from another form of energy.

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• describe the energy transformations that occur in collisions When objects collide most of their kinetic energy is transformed into other forms of energy. These forms include: - Potential energy of deformation. This is the energy stored in an object as a result of changing its shape. Sometimes that potential energy of deformation can be easily transformed back into other forms when the object returns to its original shape. - Sound energy. Sound energy is transmitted through the air as a result of vibrating particles. When a vehicle collides with an object of another vehicle, some of its kinetic energy is transferred to the surrounding air, causing rapid vibrations. - Thermal energy. Thermal energy is the enrgy that a substance posseses as a result of the random movement within them. The vehicle, air, road become heated during a collision.

• define the law of conservation of energy Energy cannot be created or destroyed but it can be transformed from one form to another.

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5. Safety devices are utilized to reduce the effects of changing momentum

• define the inertia of a vehicle as its tendency to remain in uniform motion or at rest

Inertia is the tendency of an object to resist a change in its motion. Inertia is not a force; it is a property of all objects. The inertia of an objects depends only on its mass. Inertia of a vehicle is its tendency to remain at a uniform motion. That is why in collisions, a person’s inertia can be a serious problem. When a passenger in a fast-moving car is suddenly stopped, the passenger would continue to move at a high seed until a non-zero force stopped you. Your inertia would resist the change in motion.

• discuss reasons why Newton’s First Law of Motion is not apparent in many real world situations

Newton’s first law is not apparent in everyday situations as there are usually many external forces acting upon objects on the Earth’s surface. It can be observed to some degree, however, when a car is unable to change its velocity on an icy surface, or when an object travels through space.

• assess the reasons for the introduction of low speed zones in built-up areas and the addition of air bags and crumple zones to vehicles with respect to the concepts of impulse and momentum

1) Seat Belts

A seat belt is a safety harness designed to secure the occupant of a vehicle against harmful movement that may result from a collision. As part of an overall occupant restraint system, seat belts are intended to reduce injuries by stopping the wearer from hitting hard interior elements of the vehicle or other passengers and by preventing the passenger from being thrown from the vehicle.

Most seat belts are equipped with locking mechanisms (or inertia reels) that tighten the belt when pulled fast (e.g. by the quick force of a passenger's body during a crash) but do not tighten when pulled slowly. This is implemented with a centrifugal clutch, which engages as the reel spins quickly. Alternatively, this function may be secured by a weighted pendulum or ball bearing: when these are deflected by deceleration or roll-over they lock into pawls on the reel.

Types of inertia reel type seatbelts:

NLR (No Locking Retractor): Commonly used in recoiling lap belts

ELR V (Emergency Locking Retractor - Vehicle sensitive): Single sensitive mechanism, composed of a locking mechanism activated in an emergency by deceleration or rollover of the vehicle. Thus, the seatbelt is sensitive to the vehicle's motion.

ELR VW (Emergency Locking Retractor - Vehicle and Webbing sensitive): Dual sensitive means a seatbelt retractor that, during normal driving conditions, allows freedom of movement by the wearer of the seatbelt by means of length-adjusting

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components that automatically adjust the strap to the wearer, with a locking mechanism that is activated by at least one of the following:

• deceleration or rollover of the vehicle, • acceleration of the strap (webbing) from the retractor

2) Crumple Zones

Crumple zones are areas of a vehicle that are designed to deform and crumple in a collision. This absorbs some of the energy of the impact, preventing it from being transmitted to the occupants. Crumple zones accomplish two safety goals. They reduce the initial force of the crash, and they redistribute the force before it reaches the vehicle's occupants. The best way to reduce the initial force in a crash with a given amount of mass and speed is to slow down the deceleration. An example of this is slamming on your brakes for any reason. The forces you experience in an emergency stop are much greater than when you gradually slow down for a stoplight. In a collision, slowing down the deceleration by even a few tenths of a second can create a drastic reduction in the force involved.

Since Force = Mass X Acceleration

Cutting the deceleration in half also cuts the force in half. Therefore, changing the deceleration time from .2 seconds to .8 seconds will result in a 75 percent reduction in total force.

Crumple zones accomplish this by creating a buffer zone around the perimeter of the car. Certain parts of a car are inherently rigid and resistant to deforming, such as the passenger compartment and the engine. If those rigid parts hit something, they will decelerate very quickly, resulting in a lot of force. Surrounding those parts with crumple zones allows the less rigid materials to take the initial impact. The car begins decelerating as soon as the crumple zone starts crumpling, extending the deceleration over a few extra tenths of a second.

Crumple zones also help redistribute the force of impact. All of the force has to go somewhere. Think of the force involved in a crash as a force budget. Everything that happens to the car during an impact and every person inside of the car at the time of the impact spends some of the force. If the car hits a non-stationary object, like a parked car, then some force is transferred to that object. If the car hits something with a glancing blow and spins or rolls, much of the force is spent on the spinning and rolling. If parts of the car fly off, even more force is spent. Most importantly, damage to the car itself spends force. Bending parts of the frame, smashing body panels, shattering glass -- all of these actions require energy. Think of how much force is needed to bend the steel frame of a car. That amount of force is spent on bending the frame, so it is never transmitted to the occupants.

Crumple zones are based on that concept. Parts of the car are built with special structures inside them that are designed to be damaged, crumpled, crushed and broken. The fundamental idea is that it takes force to damage them. Crumple zones

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spend as much force as possible so that other parts of the car as well as the occupants don't suffer the effects.

3) Airbags

The primary purpose of the airbag is to slow the passenger’s speed to zero with little or no damage. The constraints that it has to work within are huge. The airbag has the space between the passenger and the steering wheel or dashboard and a fraction of a second to work with. Even that tiny amount of space and time is valuable, however, if the system can slow the passenger evenly rather than forcing an abrupt halt to his or her motion.

The goal of an airbag is to slow the passenger's forward motion as evenly as possible in a fraction of a second. There are three parts to an airbag that help to accomplish this feat: - The bag itself is made of a thin, nylon fabric, which is folded into the steering

wheel or dashboard or, more recently, the seat or door. - The sensor is the device that tells the bag to inflate. Inflation happens when

there is a collision force equal to running into a brick wall at 10 to 15 miles per hour (16 to 24 km per hour). A mechanical switch is flipped when there is a mass shift that closes an electrical contact, telling the sensors that a crash has occurred. The sensors receive information from an accelerometer built into a microchip.

- The airbag's inflation system reacts sodium azide (NaN3) with potassium nitrate

(KNO3) to produce nitrogen gas. Hot blasts of the nitrogen inflate the airbag.

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Physics behind the Airbag:

RULE: force and time are inversely proportional.

F*t = Impulse

Therfore F = Impulse / t

An object with 100 units of momentum must experience 100 units of impulse in order to be brought to a stop. Any combination of force and time could be used to produce the 100 units of impulse necessary to stop an object with 100 units of momentum.

Eg: Force = 100 Time = 1 Impulse =100

Force = 1 Time = 100 Impulse =100

As can be observed, the greater the time over which the collision occurs, the smaller the force acting upon the object. Thus, to minimize the affect of the force on an object involved in a collision, the time must be increased.

Air bags use this physics phenomena to their advantage. Air bags are used in automobiles because they are able to minimize the affect of the force on an object involved in a collision. Air bags accomplish this by extending the time required to stop the momentum of the driver and passenger. When encountering a car collision, the driver and passenger tend to keep moving in accord with Newton's first law. Their motion carries them towards a windshield which results in a large force exerted over a short time in order to stop their momentum. If instead of hitting the windshield, the driver and passenger hit an air bag, then the time duration of the impact is increased. When hitting an object with some give such as an air bag, the time duration might be increased by a factor of 100. Increasing the time by a factor of 100 will result in a decrease in force by a factor of 100.

Thus the use of the airbag decreases the overall force that is applied on the passenger resulting in less serious injuries and thus saves lives.

4) Introduction of low speed zones

Low speed zones keep the risk of major damage to a minimum by decreasing the momentum of cars. Momentum increases with both velocity and mass, as shown in the equation mvp = .

It is important to keep momentum low because in TPF

ΔΔ= , as the momentum (P)

increases, so does the force (F). Lower speed zones also allow for a shorter stopping distance.

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Fmus2

2

= ,

In this equation where s is the stopping distance, m is the mass of the vehicle, u is the initial speed and F is the force of friction, m and F are constants. Therefore, if the initial speed is doubled, the stopping distance is increased fourfold. If the initial speed is halved, the stopping distance is decreased fourfold, and it can be said that the stopping distance is equal to the initial speed squared. Reducing speed decreases the chance for a collision to take place, by decreasing the stopping distance and by lowering momentum.

• evaluate the effectiveness of some safety features of motor vehicles The kinetic energy possessed by the cars is converted primarily into heat energy, sound and energy of deformation of the cars body. Let’s create a situation in which there are two cars A and B that are identical mirrors of each other. When car A collides with car B, we have different force considerations. Assuming that car A and car B are complete mirrors of each other they would collide with each other going at precisely the same speed (but opposite directions). From conservation of momentum, we know that they must both come to rest. The mass is the same. Therefore, the force experienced by car A and car B are identical and are identical to that acting on the car in case A. Force is a vector quantity while kinetic energy is a scalar quantity, calculated with the formula K = 0.5mv2. Each car has kinetic energy K directly before the collision. At the end of the collision, both cars are at rest, and the total kinetic energy of the system is 0. Since these are inelastic collisions, the kinetic energy is not conserved, but total energy is always conserved, so the kinetic energy "lost" in the collision has to convert into some other form - heat, sound, etc. In this case there are two cars moving, so the total energy released during the collision is 2K.

In summary the kinetic energy possessed by the car is converted primarily into heat energy, sound and energy of deformation of the cars body.

1) Seat Belts In Australia, in 2007, 44 drivers and passengers killed were unrestrained.

Failure to wear a seat belt contributes to more fatalities than any other single traffic safety-related behavior. 63% of people killed in accidents are not wearing seat belts. Wearing a seat belt use is still the single most effective thing we can do to protect ourselves in case of an accident.

Seat belts are the most effective safety devices in vehicles today, estimated to save 9,500 lives each year. Yet only 68 percent of the motor vehicle occupants are buckled. In 1996, more than 60 percent of the occupants killed in fatal crashes were unrestrained.

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If 90 percent of driver and passengers buckle up, we will prevent more than 5,500 deaths and 132,000 injuries annually.

2) Airbags

Government safety statistics show a continuing drop in airbag-related deaths and injuries as technology and seat beat use improves.

Two children died in last year as a result of injuries caused by airbags. No adults were killed according to the National Highway Traffic Safety Administration (NHTSA). That is an improvement over previous years.

While the reduced number of deaths and injuries can be attributed to better airbag technology, more people are wearing seat belts and more children and infants are being placed in the back seat.

1997 was the worst year for airbag-related deaths and injuries when 53 people died including 31 children. Airbags have killed 264 people since NHTSA became keeping a record of the deaths and injuries.

On the other hand, NHTSA estimates that airbags have saved almost 20,000 lives.

There is, however, a continuing problem with airbags failing to deploy in accidents. There are no reliable statistics on how many deaths and injuries have been caused by such incidents.

Advanced frontal airbag technologies vary but most airbags are designed to deploy with varying strength depending on the size and location of vehicle occupants and

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whether those occupants are wearing seat belts. Sensors built into the passenger compartment determine the power of deployment.

NHTSA statistics show that newer cars and trucks have the best airbag records. No deaths were reported from the 2002 and 2003 model years. One death was reported from the 2004 model year.

Critics argue that even the newest airbags still are capable of inflicting injuries and ought to be a matter of choice and not government mandate.

Overall in summary, there is still some controversy on the ability of airbags to help save lives in accidents. Statistics show that the use of airbags has prevented many deaths on our roads but there are others that show the deaths that are caused by the airbags. With present technology as it is, airbags seem to be doing their job for the most part and as technology improves and methods of releasing airbags faster are developed, the statistics will only improve.