Physics, Collision and Safe Driving

Categories: PhysicsSafe Driving

The potential dangers of loose objects in vehicles are strongly associated with Newton’s First Law of Motion, inertia. Inertia is when an object in motion tries to stay in motion, and an object at rest tries to remain at rest, unless the object is acted upon by an outside force. For example, say a car is traveling along a straight road. Loose objects in the auto are “acted upon” by the body, seats, or some other part of the vehicle (whatever is touching a loose object), whenever the whole thing accelerates.

The two most important things related to this are:

  1. “Velocity” is a concept that includes both the speed and the direction of motion
  2. “Acceleration” exists whenever there is any change in a velocity

Let us first return to the straight road, and magically do two things:

  1. Stop the car instantly.
  2. Turn the car so that if faces left, also instantly.

What happens to all the loose objects inside the car? They are still going to obey the First Law of Motion, and try to continue going down the straight road.

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However, since the car is now both stopped and facing left, the right wall of the car is in everything’s way. At that moment everything flies towards the right wall, and the loose objects crash hard against it. Also, the driver and the passenger(s) would also smash into the right wall.

If the car was extremely heavy, or was traveling at a considerable speed, then the force of the crash would be greater.

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This is because of Newton’s second law, F=ma, the larger the acceleration or mass, the greater the force. This makes it obvious that loose objects in vehicles is dangerous and should be placed in compartments provided.

The whole point of this is that when an auto merely follows the curve of the road towards the left, a less drastic version of the same thing happens: the right wall of the vehicle gets in the way of every loose object’s natural tendency to keep going straight. When each object comes to rest against that wall, then it begins experiencing acceleration towards it own left. At the end of the curve, when the auto goes straight again, everything in it will have finished accelerating towards the left, so the various objects will lay loosely once more.

Avoiding or reducing the effect of a collision

In a collision, an object experiences a force for a given amount of time which results in its mass undergoing a change in velocity (i.e. which results in a momentum change). Technologies have greatly improved our ability to avoid or reduce the effect of a motor vehicle collision. Many are now considered to be standard features. Others optional extras, and some are only found in the most luxurious cars. The main focus in reducing the effect of a collision if to reduce the force the person feels during a collision. To do this, you need to maximize the distance over which the person comes to rest. This is derived from the formula Fd=k (where k is a constant value of kinetic energy). This means that force and stopping distance are inversely proportional to each other. It is known that the force (F) is the final value that determines the extent of the collision both on the vehicle and its occupants. Crumple zones, seatbelts and air bags are three examples of technology that are based upon this concept, and Newton’s first law of motion, “the object in motion continues to move with a speed that is constant in magnitude and direction.”

A car’s crumple zones do the real work of increasing the stopping distance, thus softening the blow. Crumple zones are areas in the front and rear of a car that collapse relatively easily. Instead of the entire car coming to an abrupt stop when it hits an obstacle, it absorbs some of the impact force by flattening, like an empty soda can. The car’s cabin is much sturdier, so it does not crumple around the passengers. It continues moving briefly, crushing the front of the car against the obstacle. Of course, crumple zones will only protect the person if he or she is secured to the seat by the seatbelt.

A seatbelt’s job is to spread the stopping force across sturdier parts of your body in order to minimize damage. A typical seatbelt consists of a lap belt, which rests over the pelvis, and a shoulder belt, which extends across the chest. The two belt sections are tightly secured to the frame of the car in order to hold passengers in their seats.

When the belt is worn correctly, it will apply most of the stopping force to the rib cage and the pelvis, which are relatively sturdy parts of the body. Since the belts extend across a wide section of the body, the force isn’t concentrated in a small area, so it can’t do as much damage. Additionally, the seatbelt webbing is made of more flexible material than the dashboard or windshield. It stretches a little bit, which means the stop isn’t quite so abrupt.

An air bag is an inflation system made of a thin, nylon fabric folded into the steering wheel or dashboard or, for side airbags, the seat or door. The air bag has a sensor that tells the bag to inflate. The mechanical switch is flipped when there is a mass shift that closes an electrical contact, telling the sensors that a crash has just occurred.

The air bag system ignites a solid propellant, which burns rapidly to create a large volume of nitrogen gas to inflate the bag. The bag then literally explodes from its storage site. A split second later, the gas quickly disappears through tiny holes in the bag, thus deflating the bag so the driver or passenger can move.

Cite this page

Physics, Collision and Safe Driving. (2016, Jul 23). Retrieved from

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