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Chapter 5 -- Part 2
The average speed.
There is a collision protective device.
The strength of body tissue is estimated.
The average stopping force and force per cm2 are at a 105 km impact speed.
The passenger would probably be hurt by the force.
The possibility that the bag may be triggered during normal driving has been considered in the design of this safety system.
If the bag were to remain expanded, it would make it harder for the driver to control the vehicle, so the bag is only expanded for a short time to cushion the impact.
Neck bones can be fractured by a moderate force.
If the impact is sudden, as in a rear-end collision, the body is accelerated in the forward direction by the back of the seat, and the neck is suddenly pulled back at full speed.
People who jumped out of airplanes with parachutes that failed to open and then survived because they landed on soft snow have been reported.
The body made a 1-m deep depression in the snow on impact.
The impact force that acts on the body during a landing can be calculated to verify the credibility of these reports.
We discussed the damaging effects of large impulsive forces in the beginning of the chapter.
The impact of feet with the ground in walking and running is one of the smaller repetitive forces that our bodies are subject to.
There is still a question as to the extent of the smaller repetitive forces that are encountered in exercise and sport.
Osteoarthritis is often caused by repetitive impact.
Osteoarthritis is a joint disease caused by wear and tear on the components of the joint.
The joint loses strength and flexibility as a result of wear and tear.
The underlying bone may begin to erode.
Osteoarthritis is a major cause of disability.
The most common affected joint is the knee.
The majority of men and women are affected by this condition after the age of 65.
A number of studies have been done to determine the link between exercise and arthritis.
The conclusion is that joint injury is related to osteoarthritis.
People who engage in high impact injury prone sports are more likely to have osteoarthritis.
There appears to be little risk associated with running 20 to 40 km a week.
An injured joint is more likely to wear and tear over time.
Un-lubricated bones have a higher coefficient of friction.
The ability of the joint to lubricate is usually compromised by a joint injury.
A simple picture would lead one to believe that the progress of osteoarthritis would be more rapid in the joints of people who are regular runners than in a control group of non- runners.
This doesn't seem to be the case.
Osteoarthritis seems to progress at the same rate in both groups, indicating that the joints have the ability to repair themselves.
The conclusions are subject to further study.
A 50 kilo runner trips and falls on his hand.
The length of the arm is 1 m and the area of the bone is 4 cm2.
The area of impact is 4 cm2 and the duration is 10-2 seconds.
The area of impact is 1 cm2.
Assume that the object is hard, that the area of contact with the skull is 1 cm2, and that the impact time is 10 to 3 seconds.
If you use the data provided in the text, you can figure out the mass of the head and the area of the neck.
A boxer is punching a bag.
His fist hits the bag at a speed of 7 m/s.
His hand came to a stop as a result of hitting the bag.
If the moving part of his hand is less than 5 kilo, you can calculate the rebound velocity and energy of the bag.
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