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Force of impact: F = m x a

What sort of forces were involved here?

What sort of forces were involved here?

Cast your mind back a little… do you remember what you learned in physics in school about kinetic energy? This referred to energy forces from “things in motion” and “impact”? We learned that the weight of an object and its speed have a direct impact on the outcome. Realistically if you double the weight of the object you double the energy; but if you double the speed of the object, you quadruple the energy. As paramedics we apply this principle daily when we consider the seriousness of the injuries any patient may have sustained because we know that it is proportional to the amount of energy transferred and the ability of the body to resist that energy.

When this principle is applied in the context of road traffic collisions clearly speed is the greatest determinant of the forces involved. Other factors such as any pre-existing medical conditions and age should also be considered as they can make a person more vulnerable to these forces. When you arrive on scene, even if your patient ‘looks well’ it is still crucial to find out exactly what happened and the mechanism of injury before you accept this at face value. Don’t be fooled just because they initially appear to be all in one piece.  For example, if the history given to you is of a person who while standing next to a stationary bus fell over, banging their head, the transfer of energy could be assumed to be fairly minimal even though they have  ‘struck a bus’. If however, reports suggest that the bus was moving at 30 miles per hour when it struck your patient, clearly the energy transference is far greater and it is very probable that they will have sustained a significant injury such as tearing of muscles, blood vessels, broken bones or damage to internal organs.

Every object continues in a state of rest, or of uniform motion in a straight line, unless it is compelled to change that state by forces acting upon it.”

Sir Isaac Newton (1643-1727)

When I was called to a man hit by a bus recently the thought occurred to me that if I had arrived from the top of the road and not seen the damage to the front of the bus I may have been fooled into thinking that my patient’s injuries were likely to be very minor. He was lying in the road, not only fully conscious but very chatty and apart from a laceration to his head seemed to be all in one piece.  However, I had arrived from the bottom of the road and when I first saw the damage to the bus I initially wondered if a car had taken off and launched itself in to the front of it! Unbelievably this damage was all done by the patients head and body.

So even though the patient was stable, the HEMS team were activated. We immobilised him on scene and managed his pain; he was then transferred to a trauma unit for further assessment of the extent of his injuries. I am waiting to hear about the outcome for this patient and will update this post when I find out.


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  1. [...] I am not suggesting that when you fall from a second floor window or get hit by a bus you should crawl to the nearest chemist to purchase a packet of paracetamol and a band-aid. [...]

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