Tension
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In physics, tension is described as the pulling force transmitted axially by the means of a string, a rope, chain, or similar object, or by each end of a rod, truss member, or similar three-dimensional object; tension might also be described as the action-reaction pair of forces acting at each end of said elements. Tension could be the opposite of compression.
At the atomic level, when atoms or molecules are pulled apart from each other and gain potential energy with a restoring force still existing, the restoring force might create what is also called tension. Each end of a string or rod under such tension could pull on the object it is attached to, in order to restore the string/rod to its relaxed length.
Tension (as a transmitted force, as an action-reaction pair of forces, or as a restoring force) is measured in newtons in the International System of Units (or pounds-force in Imperial units). The ends of a string or other object transmitting tension will exert forces on the objects to which the string or rod is connected, in the direction of the string at the point of attachment. These forces due to tension are also called \"passive forces\". There are two basic possibilities for systems of objects held by strings:[1] either acceleration is zero and the system is therefore in equilibrium, or there is acceleration, and therefore a net force is present in the system.
Tension in a string is a non-negative vector quantity. Zero tension is slack. A string or rope is often idealized as one dimension, having length but being massless with zero cross section. If there are no bends in the string, as occur with vibrations or pulleys, then tension is a constant along the string, equal to the magnitude of the forces applied by the ends of the string. By Newton's third law, these are the same forces exerted on the ends of the string by the objects to which the ends are attached. If the string curves around one or more pulleys, it will still have constant tension along its length in the idealized situation that the pulleys are massless and frictionless. A vibrating string vibrates with a set of frequencies that depend on the string's tension. These frequencies can be derived from Newton's laws of motion. Each microscopic segment of the string pulls on and is pulled upon by its neighboring segments, with a force equal to the tension at that position along the string.
Tension is also used to describe the force exerted by the ends of a three-dimensional, continuous material such as a rod or truss member. In this context, tension is analogous to negative pressure. A rod under tension elongates. The amount of elongation and the load that will cause failure both depend on the force per cross-sectional area rather than the force alone, so stress = axial force / cross sectional area is more useful for engineering purposes than tension. Stress is a 3x3 matrix called a tensor, and the σ 11 {\\displaystyle \\sigma _{11}} element of the stress tensor is tensile force per area, or compression force per area, denoted as a negative number for this element, if the rod is being compressed rather than elongated.
String-like objects in relativistic theories, such as the strings used in some models of interactions between quarks, or those used in the modern string theory, also possess tension. These strings are analyzed in terms of their world sheet, and the energy is then typically proportional to the length of the string. As a result, the tension in such strings is independent of the amount of stretching.
A tension-type headache (TTH) is generally a mild to moderate pain that's often described as feeling like a tight band around the head. A tension-type headache is the most common type of headache, yet its causes aren't well understood.
Treatments for tension-type headaches are available. Managing a tension-type headache is often a balance between practicing healthy habits, finding effective nondrug treatments and using medications appropriately.
Episodic tension-type headaches can last from 30 minutes to a week. Frequent episodic tension-type headaches occur less than 15 days a month for at least three months. Frequent episodic tension-type headaches may become chronic.
Unlike some forms of migraine, tension-type headaches usually aren't associated with visual disturbances, nausea or vomiting. Although physical activity typically aggravates migraine pain, it doesn't make tension-type headache pain worse. An increased sensitivity to either light or sound can occur with a tension-type headache, but this symptom isn't common.
The cause of tension-type headaches is not known. Experts used to think tension-type headaches stemmed from muscle contractions in the face, neck and scalp, perhaps as a result of heightened emotions, tension or stress. But research suggests that muscle contraction isn't the cause.
The most common theory supports a heightened sensitivity to pain in people who have tension-type headaches. Increased muscle tenderness, a common symptom of tension-type headaches, may result from a sensitized pain system.
Because tension-type headaches are so common, their effect on job productivity and overall quality of life is considerable, particularly if they're chronic. The frequent pain may render you unable to attend activities. You might need to stay home from work, or if you do go to your job, your ability to function may be impaired.
Tension headaches are the most common type of headache. Stress and muscle tension are often factors in these headaches. Tension headaches typically don't cause nausea, vomiting, or sensitivity to light. They do cause a steady ache, rather than a throbbing one, and tend to affect both sides of the head. Tension headaches may be chronic, occurring often, or every day.
The exact mechanism that causes a tension headache is not known. Several factors, such as genetics and environment, are thought to be involved. Muscle contractions in the head and neck are considered a major factor in the development of a tension headache. Some people get tension headaches in response to stressful events or hectic days.
If the history suggests tension headaches and the neurological exam is normal, no further testing may be needed. But, if the headache is not found to be the main problem, then other tests may be needed to determine the cause such as:
Identifying and avoiding headache triggers may prevent a tension headache. Maintaining a regular sleep, exercise, and meal schedule is also helpful. If tension headaches occur regularly or frequently, therapies such as cognitive-behavioral therapy, relaxation therapy, or biofeedback may reduce or eliminate headaches. Talk to your healthcare provider about medicines to prevent tension headaches.
People experience tension headache symptoms differently. Some people describe tension headache pain as feeling like someone (or something) is squeezing both sides of their head together or a band around their head.
People with chronic tension-type headaches can have symptoms that last for months at a time. Pain may stay at the same level of discomfort for days. While uncommon, these headaches can take a toll on your quality of life.
Sometimes tension-type headaches may be a sign of an underlying disorder such as thyroid disease or an underlying tumor or a primary headache disorder, such as chronic migraine or new daily persistent headache. Anyone over age 50 with a new onset headache should see their doctor for an evaluation .
Researchers have yet to uncover how to prevent all headaches. If you experience chronic tension-type headaches or frequent tension-type headaches certain medications may stop some headaches before they start. These are antidepressants such as amitriptyline or venlafaxine or duloxetine. These work on the pain centers in the brain.
Overall, lifestyle changes and reducing your response to stress is the best way to prevent tension headaches. The most effective stress management tool is the one that fits into your life and you feel good using. You may want to try:
Pneumothorax is when air collects in between the parietal and viscera pleurae resulting in lung collapse. It can happen secondary to trauma (traumatic pneumothorax). When mediastinal shifts accompany it, it is called a tension pneumothorax. This is a life-threatening emergency that needs urgent management. Early recognition of this condition is life-saving both outside the hospital and in modern ITUs. Knowledge of necessary emergency thoracic decompression procedures is essential for all healthcare professionals. This activity reviews the presentation of tension and traumatic pneumothoraces, outlines evaluation and management strategies, and highlights the importance of early intervention and the role of the interprofessional team in evaluating and improving care for patients with this condition.
Objectives:Identify the pathophysiology of tension pneumothorax.Describe the appropriate evaluation of tension pneumothorax.Review the management options available for tension pneumothorax.Explain the importance of improving care coordination among interprofessional team members to provide the best outcomes for patients with tension pneumothorax.Access free multiple choice questions on this topic.
Pneumothoraces are classified as simple (no shift of mediastinal structures), tension (shift in mediastinal structures present), or open (air passing through an open chest wound). Tension pneumothorax is an uncommon condition with a malignant course that might result in death if left untreated.[1][2] It is a severe condition that results when air is trapped in the pleural space under positive pressure, displacing mediastinal structures and compromising cardiopulmonary function. It is most commonly encountered in the prehospital, emergency department, and intensive therapy unit (ITU) settings.[3][4][5][6]
Early recognition of this condition is life-saving both outside the hospital and in modern ITUs. Knowledge of necessary emergency thoracic decompression procedures is essential for all healthcare professionals. Traumatic and tension pneumothoraces are life-threatening and require immediate treatment.[7] 59ce067264
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