Statics plays an important part in understanding everyday strains in our muscles and bones.
Many lever systems in the body have a mechanical advantage of significantly less than one, as many of our muscles are attached close to joints.
Someone with good posture stands or sits in such as way that their center of gravity lies directly above the pivot point in their hips, thereby avoiding back strain and damage to disks.
Conceptual questions
Why are the forces exerted on the outside world by the limbs of our bodies usually much smaller than the forces exerted by muscles inside the body?
Explain why the forces in our joints are several times larger than the forces we exert on the outside world with our limbs. Can these forces be even greater than muscle forces?
Certain types of dinosaurs were bipedal (walked on two legs). What is a good reason that these creatures invariably had long tails if they had long necks?
Swimmers and athletes during competition need to go through certain postures at the beginning of the race. Consider the balance of the person and why start-offs are so important for races.
Suppose the biceps muscle was attached through tendons to the upper arm close to the elbow and the forearm near the wrist. What would be the advantages and disadvantages of this type of construction for the motion of the arm?
The upper leg muscle (quadriceps) exerts a force of 1250 N, which is carried by a tendon over the kneecap (the patella) at the angles shown in
[link] . Find the direction and magnitude of the force exerted by the kneecap on the upper leg bone (the femur).
The knee joint works like a hinge to bend and straighten the lower leg. It permits a person to sit, stand, and pivot.
A device for exercising the upper leg muscle is shown in
[link] , together with a schematic representation of an equivalent lever system. Calculate the force exerted by the upper leg muscle to lift the mass at a constant speed. Explicitly show how you follow the steps in the Problem-Solving Strategy for static equilibrium in
Applications of Statistics, Including Problem-Solving Strategies .
A mass is connected by pulleys and wires to the ankle in this exercise device.
A person working at a drafting board may hold her head as shown in
[link] , requiring muscle action to support the head. The three major acting forces are shown. Calculate the direction and magnitude of the force supplied by the upper vertebrae
to hold the head stationary, assuming that this force acts along a line through the center of mass as do the weight and muscle force.
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