Common Thoughts About Force Involved In Motor Vehicle Accidents

A while back I received a rude response to my, “What happens in a car accident,” article. I was really surprised by the comment of the reader so I decided to do a little experiment and also poll a greater population to get an understanding of general impressions of what happens when a car strikes an object. Before I get to the experiment results and the pole results I will quote a class on Motor Vehicle accident:
“The acceleration-deceleration forces which cause whiplash injury are sufficient to permanently disable an individual. Even in a low speed rear impact collision of 8 mph, the head moves roughly 18 inches, at a force as great as 7 G’s in less than a quarter of a second. To put this into perspective, the Discovery space shuttle is only built to withstand a maximum of 3 G’s.”
“Newton's first law states that an object at rest tends to stay at rest and an object in motion tends to stay in motion with the same speed and in the same direction unless acted upon by an unbalanced force.
If an object is in motion with an eastward velocity of 5 meters per second, it will continue in this same state of motion (5 m/s, East). If in motion with a leftward velocity of 2 m/s, it will continue in this same state of motion (2 m/s, left). The state of motion of an object is maintained as long as the object is not acted upon by an unbalanced force. All objects resist changes in their state of motion.
Inertia (resisting changes in the state of motion) occurs in an automobile while it is braking to a stop. The force of the road on the locked wheels provides the unbalanced force to change the car's state of motion, however there is no unbalanced force to change the passenger’s own state of motion. Therefore, the passenger continues in motion, sliding forward along their seat. A person in motion tends to stay in motion with the same speed and in the same direction ... unless acted upon by the unbalanced force of a seat belt. The seat belt provides the unbalanced force which brings the occupant of a vehicle from a state of motion to a state of rest. “
“Force is a quantity which is measured using a standard metric unit known as the Newton. One Newton is the amount of force required to give a 1-kg mass an acceleration of 1 m/s2. A Newton is abbreviated by an "N."
Force is a vector quantity. A vector quantity is a quantity which has both magnitude and direction. To describe the force acting upon an object, you must describe both its magnitude (size) and its direction. Thus, 10 Newtons is not a full description of the force acting upon an object. In contrast, 10 Newtons, downwards is a complete description of the force acting upon an object; both the magnitude (10 Newtons) and the direction (downwards) are given.”
“The mass of an object (measured in kg) will be the same no matter where in the universe that object is located. Mass is never altered by location, the pull of gravity, speed or even the existence of other forces. For example, a 2-kg object will have a mass of 2 kg whether it is located on Earth, or the moon.
The weight of an object (measured in Newtons) will vary according to where in the universe the object is. Weight depends upon which planet is exerting the force and the distance the object is from the planet. Weight, being equivalent to the force of gravity, is dependent upon the value of g (acceleration of gravity). On Earth's surface, g is 9.8 m/s2 (often approximated to 10 m/s2). On the moon's surface, g is 1.7 m/s2. The g value is inversely proportional to the distance from the center of the planet. So if g were measured at a distance of 400 kilometers above the earth's surface, you would find the value of g to be less than 9.8 m/s2.”2

“Newton's second law of motion pertains to the behavior of objects when all existing forces are not balanced. The second law states that the acceleration of an object is dependent upon two variables – the net force acting upon the object and the mass of the object. The acceleration of an object depends directly upon the net force acting upon the object, and inversely upon the mass of the object. As the net force increases, so will the object's acceleration. However, as the mass of the object increases, its acceleration will decrease.”

“A force is a push or a pull upon an object which results from its interaction with another object. According to Newton, whenever objects A and B interact with each other, they exert forces upon each other. When you sit in your chair, your body exerts a downward force on the chair and the chair exerts an upward force on your body. There are two forces resulting from this interaction — a force on the chair and a force on your body. These two forces are called action and reaction forces.
Newton's third law states that for every action, there is an equal and opposite reaction. The statement means that in every interaction, there is a pair of forces acting on the two interacting objects. The size of the force on the first object equals the size of the force on the second object. The direction of the force on the first object is opposite to the direction of the force on the second object. Forces always come in pairs – equal and opposite action-reaction force pairs. An example of this would be force generated by the wheels of a car. An automobile is equipped with wheels that spin backwards. As the wheels spin backwards, they push the road backwards. In turn, the road reacts by pushing the wheels forward. The size of the force on the road equals the size of the force on the wheels (or automobile); the direction of the force on the road (backwards) is opposite to the direction of the force on the wheels (forwards). For every action, there is an equal (in size) and opposite (in direction) reaction. Action-reaction force pairs make it possible for automobiles to move.”

Now the experiment I did was as follows: I took a 2x4 and a ¾” Plywood that measured 2 feet by 2 feet. I placed the board on a 30 degree angle and stood on it with my 220 pound body and then I bounced on the board. I then took and did the same thing to the piece of plywood. Then I took duplicate boards and leaned them at a 30 degree angle against the house and pulled my van up to the boards. When I put the van into drive the force of the van cracked the boards. My weight and bouncing alone was not sufficient to crack the boards before.
The poling of the people went as follows: I asked twenty four people one at a time to give me their opinion about two scenarios I would present. I asked twelve females and twelve males. Out of that population three were engineers, one was an ex law enforcement officer, one was a lawyer, the remaining of the group had at least one year of college. Out of that group the engineers and the ex law enforcement officer answered the same. The two scenarios were as follows:
Two identical individuals were standing beside each other on a road, one in the right lane and the other in the left lane. Ten feet from them was a Honda civic in the right lane and a 220 pound linebacker in the left lane. The Honda civic and the linebacker started towards the two individuals standing in the road. The Honda was traveling 5 miles per hour and the linebacker was traveling 14 miles per hour. Which individual sustained the most amount of damage if they were hit in the same place on their body? The engineers and officer familiar with physics answered that the person hit by the Honda civic would sustain more damage because the force was greater from the Honda civic. That might sound weird but just recently I have a patient who told me about getting hit over twenty years ago in a parking lot. He was a pedestrian and the car that hit him was traveling about 5 miles per hour in the parking lot. He can still recall the thud he felt and that he came right out of his shoes. He says he still hurts from that hit.
The second scenario was in relationship to momentum and again only the individuals familiar with physics came up with the same answer. The poling population would need to be expanded but the preliminary response shows me that the general population can pass some wrong judgments because the understanding of physics is less. Maybe that is the way several things are. We judge harder the things we do not fully understand, and the more knowledge we obtain might cause us to judge less harshly.