# Tension

JoVE Core
Mechanical Engineering
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JoVE Core Mechanical Engineering
Tension

### Nächstes Video1.13: Gravitational Force

Tension is described as the force associated with a tightly pulled string, rope, or cable. It is a pulling force, as it can only pull an object and cannot push one.

When a rope is pulled tight, the tension force is transferred through the rope to the attached object. Here, the tension force balances the weight of the object.

Consider a box of mass 'm' being pulled by a string at an angle theta on a smooth surface with acceleration 'a'.

In this situation, the forces on the box are the gravitational pull acting downward, the normal force acting upward, and the tension force along the pulled string.

The x-component of the tension is the only force acting in the horizontal direction.

In the vertical direction, the y-component of tension acts upward along with the normal force, and the gravitational pull acts downward.

Applying Newton's second law to the system gives the tension force exerted by the string and the normal force exerted by the surface on the box.

## Tension

Tension is a force along the length of a medium, in particular, a force carried by a flexible medium, such as a rope or cable. The word "tension" comes from Latin, meaning "to stretch". Not coincidentally, the flexible cords that carry muscle forces to other parts of the body are called tendons. Any flexible connector, such as a string, rope, chain, wire, or cable, can exert pull only parallel to its length; so, a force carried by a flexible connector is a tension with a direction parallel to the connector. It is important to understand that tension is a pull in a connector. Consider the saying "you can't push a rope"; tension force only pulls outward along the two ends of a rope.

Flexible connectors are often used to transmit forces around corners, such as in a hospital traction system, a finger joint, or a bicycle brake cable. If there is no friction, the tension is transmitted undiminished. Only its direction changes, and it is always parallel to the flexible connector. For instance, tendons in the finger carry force from the muscles to other parts of the finger, usually changing the force's direction but not its magnitude. The tendons are relatively friction-free. Similarly, a brake cable on a bicycle carries the tension from the handlebars to the brake mechanism. Again, the direction, but not the magnitude, of the tension force is changed.