If the pulleys are not moving, the force is an integral multiple of tension.
The pulley system has two cables attached to it's load.
The machine has something.
The load has three cables attached to it.
The system of interest is being pulled on by four cables.
The most interesting applications of statics are the muscles, bones, and joints.
There are some surprises.
We might think that muscles exert less force than they really do.
The schematic is a good approximation of the forearm, which looks more complicated than it is, and we can get some insight into the way typical muscle systems function by analyzing it.
Muscles can only contract in pairs.
The bicep muscle closes the limb in the arm.
The limb is opened by the triceps muscle.
Skeletal muscles, bones, and joints in humans are typical of this configuration.
The reason is clear once we realize that most muscles are attached to bones via tendons close to joints, which causes these systems to have mechanical advantages much less than one.
The weight of the forearm and the book is supported by the biceps.
The triceps are thought to be relaxed.
You can take the data in the figure to be accurate.
The forearm has four forces acting on it.
The first condition for equilibrium cannot be achieved by itself.
The only unknown is if we use the second condition and choose the pivot to be at the elbow.
The bicep muscle exerts a force 7.38 times the weight supported.
The angle between the forearm and upper arm is shown in the above example.
The force that the biceps muscle exerts if this angle changes.
The force the biceps muscle can exert depends on its length and how stretched it is.
Large forces are created in the joints.
In the previous example, the downward force exerted by the humerus at the elbow joint was greater than the total weight supported.
Because muscles can contract, but not expand beyond their resting length, joints and muscles exert forces that act in opposite directions.
The book shows that forces in muscles and joints are the largest when their load is a long distance from the joint.
Large forces are created by the constant extension of the arm in racquet sports.
The mass of the lever arm of a tennis racquet is an important factor, and many players use the heaviest racquet they can handle.
It's no wonder that repetitive motion can cause damage to the elbow in tennis and other sports.
Various tried techniques for holding and using a racquet or bat or stick can increase sporting prowess but can minimize fatigue and long-term damage to the body.
Tennis balls hit at the "sweet spot" on the racquet will result in little impact force being felt in the racquet and the body-less Torque as explained in Collisions of Extended Bodies in Two Dimensions.
If you twist the hand to provide spin on the ball or use an extended rigid elbow in a backhand stroke, you can hurt the elbow.
The knowledge of relationships between forces and Torques is used in the treatment of muscles and joints.
In physical therapy, an exercise routine can apply a particular force and Torque which can revive muscles and joints over a period of time.
Some exercises are designed to be carried out under water because they require more force to be exerted.
The tissues in the limbs and joints can be damaged by the large forces they carry.
Heavy muscled athletes, such as weightlifters, can tear muscles and connect tissue on their own.
The back is more complicated than the arm or leg and has less mechanical advantages.
The muscles of the back must exert large forces.
Discs are often crushed by mere exertion.
The jaw's masseter muscles allow us to exert large forces with the back teeth.
A cause of stress headaches is teeth clenching which causes fatigue in the muscles around the skull.
Bad posture causes back strain.
There is a person with good posture.
The pivot point in the hips is directly above the base of support at her feet.
The only force required is a vertical force at the hips.
The bones are rigid and transmit force from the floor.
If the upper body is slightly displaced, small forces are needed to bring it back to its original position.
The upper body's cg is in front of the pivot in the hips.
The muscles in the lower back counteract the clockwise Torque around the hips.
Since they have small mechanical advantages, these muscles must exert large forces.
Poor posture can cause muscle strain for people sitting at their desks.
Special chairs allow the body's CG to be more easily positioned above the seat to reduce back pain.
Muscle strain is caused by long muscle action.
The person wouldn't be in equilibrium if this wasn't compulsory.
The back muscles must exert a large force because they have a small lever arm.
The legs lean back to keep the body above the base of support in the feet.
You should not lift objects with your back.
Since large forces are created in the back muscles and spine, this action can cause muscle strain and damage.
People change their stance to maintain balance.
The box has a mass of 30.0 kilograms and the upper body has a mass of 50.0 kilograms.
Data may be taken to be accurate to three significant figures.
If the pivot is chosen to be at the hips, the second condition for equilibrium is a good place to start, and inspection of the known values confirms that it can be used to solve the problem.
If the load were not present, the force would be smaller.
The force on the spine is more important than its damage potential.
The first condition for equilibrium can be used to find its magnitude and direction.
If the person were standing, the force would be about the same.
The problem with the back isn't so much that the forces are large, but that they are weak.
In this case, the forces in the back are about 5.6 times smaller because of proper lifting and using the legs to raise the body and load.
The back muscles exert large forces when a person lifts with their back, since they have small lever arms.
The data shown here is analyzed in the previous example.
Small muscle contractions can produce large movements of limbs in a short period of time.
Flexibility and agility are made possible by the large number of joints and the ranges over which they function.
It's hard to imagine a system with a broad range of movement that we have.
The systems of muscles, bones, and joints are complex.
As the joint is flexed, the pivot point in many joints changes location, so that the lever arms and mechanical advantage of the system change as well.
As the forearm is flexed, the force the biceps muscle exerts to hold up a book varies.
The mechanisms in the legs explain why there is less leg strain when a bicycle seat is set at the proper height.
The methods used in this section give a reasonable description of the real systems.
Some of the examples of force and Torque in the body are the subject of chapter problems.
If statics is the study of forces in equilibrium, a system is said to be in stable equilibrium.
The second condition assures that the Torques are balanced.
The angle between strain and the pivot point can be applied to a variety of situations, from raising a drawbridge to bad posture and back magnitude of the force.
The problem-solving and the force strategies directed from the point where they are useful for statics have been discussed.
The pivot point is the act of statics.
The general problem is defined to be solving strategies and the special strategies forNewton's laws are discussed in the case of the lever arm.
The newton-meter is the force that we apply at the SI unit.
The force is the second expense of a distance through which we have to apply condition to achieve equilibrium.
The counterclockwise Torques are positive, and a few simple machines are negative.
The muscles are attached to the joints.
Scissors are similar to a double-lever system.
If you pull a nail at a constant rate, you'll have to use nail forces on the body.
Give an example.
A building is being knocked down.
A tall concrete wall is still standing.
The wall our limbs are on is larger than the forces we exert on the outside world.
Some types of dinosaurs were bipedal.
There is a good reason why these creatures are so long.
Start-offs are important for races because of the balance of the person.
Explain your answer with strategies.
The data in the schematic hinges can be used to calculate the force exerted on the wall.
What Torque do you exert on the situation?
You push on a equilibrium when you tighten a bolt.
The total mass of the horse and rider is 500 wrench with a force of 165 N at a distance of 0.140 m. To be accurate, take the data to three digits.
Two children push on a door.
It's assumed that the amount of friction is negligible.
Two children of mass 20.0 and 30.0 are balanced on a pivot and assuming a seesaw with a pivot point located at the center of the mass of 12.0 kg for the seesaw.
There are other data given in the seesaw.
If the children are separated by a distance, remain the same.
The horse and rider have a mass of 500 grams.
The wall exerts horizontal force.
A person carries a plank of wood with one hand pushing down on it at one end with a force and the other hand holding it up at.500 m from the end of the plank with force.
The wall's thickness should be neglected.
The chicken has hinges, its weight, and tension in its wires, and this is supported by a small drawbridge.
The sign's mass is over 7 tons.
A sign on a sandwich board shows tension.
If you needed to change a tire, you would have to raise the mower a distance between the legs and the ground.
A gymnast is doing splits.
A tire with a radius of is used in a typical car.
The nail puller has a mass.
A gymnast splits.
The pulley system's mass should be neglected.
A pulley system's mass is placed by a person on the roof.
We can assume that the ladder rests against a plastic rain and Joints gutter.
The text states that the 407 N is.
The calcaneus bone is attached to the achilles tendon of the leg.
A mass is connected by pulleys and wires to N, which is carried by a tendon over the kneecap.
A person working at a drafting board can hold her head kneecap on the upper leg bone.
The lower leg is straightened by the knee joint.
A person can sit, stand, and pivot.
A man is standing on his toes with an upward forearm and upper arm.
The muscles at the back of the neck need to exert force to keep the head straight.
That is the reason why you fall asleep in class.
When one stands on one's toes, the muscles in the back of the leg pull.
A simplified lever system is shown.
The major point of support for the head is in front of the mass of the head.
A simplified lever system is shown.
A child is being lifted by a father.
She moves up at a constant speed if that is attached far from the joint.
Take the force of each muscle and divide it by her weight.
A woman is doing physical activity.
A person is clenching his teeth.
You planted a palm tree in your front lawn for your mother's birthday.
Hooke's Law states that if a ball falls to the ground near a tree, it obeys it.
The force of the tree's recoil is assumed to be minimal.
An effective force is the same location as the book if the rope is held in the hand at the loose.
The bicep muscle is still uprooted.
Two children are using a uniform seesaw that is 3.00 m long and has its center of mass over the pivot.
The first child has a mass of 30.0 kg and is 1.40 m from the pivot.
There is a method for measuring the mass of a person's arm.
The subject is lying on her back with her relaxed arm extended to the side.
One is under the elbow and the other under the back of her hand.
The center of mass of the arm can be calculated by taking the mass of the arm and dividing it by the distance from the shoulder joint.
A free body diagram of the arm is required to direct the analysis.
Changing the position of the scale under the hand would give more information.
References can be used to get reasonable mass values.
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