# Learn The Concept Of Stress Units Along With Types Of Motion

Stress is the basic concept of physics which explains the force acting on the object. Stress causes the body to deform and is also measurable. Let us know more about stress, its effect on the object along with the unit.

Stress is defined as the force applied per unit area of the body. Stress causes a change in the shape of the body. Depending upon the material of the object, it responds to the force applied. The object with less force bearing capacity deform more or might end up breaking in some cases. The stress-strain curve shown below, explains the exact extension of the material when stress-strain is applied.

Stress-strain varies from one material to another. Stress is a measure of the internal forces in a body between its particles. Stress can be found using the following formula:

Where,

σ is the stress

F = force

A = surface area

Stress units are the measure of the force per unit area. SI unit of stress is measured in pascals.

Stress unit = N/m^{2}

**Young’s Modulus**

Young’s modulus is a mechanical property that is used to measure the stiffness of a solid material. Young’s modulus describes the relationship between stressor force applied per unit area and strain or the deformation due to the force applied on a material. This concept was named after scientist Thomas Young.

Young’s modulus is a measure of the strength of a material to resist changes in length when lengthwise tension or compression is applied and is also known as modulus of elasticity.

In linear elasticity, A solid material experiences elastic deformation when a small load is applied to it. It leads to compression or extension in the solid material. Elastic deformation is reversible and hence the material can return to its original shape after the load is removed. Below graph explains the stress-strain relationship. It explains that stress is directly proportional to the strain.

According to the graph,

Where,

E = Young’s modulus

= uniaxial stress or force applied

= stain or resultant deformation

Units of the Young modulus E= Nm-2 or Pa

** ****Hooke’s Law**

In 1660, scientist Robert Hooke discovered Hooke’s Law also known as the law of elasticity. According to Hooke’s law, the force (F) needed to extend or compress a spring by some distance x ranges linearly with respect to the distance.

Hence,

k is a constant factor, stiffness of the spring

x= the total possible deformation of the spring

The value of k depends on the size and shape of the material

On the basis of Hooke’s law, it can be explained that at relatively large values of applied force, the deformation of the elastic material is larger than expected. Even though the material remains elastic state, it returns to its original shape and size after removal of the force.

## Motion – Types Of Motion With Relevant Examples

Let’s know what is motion and types of motion with justifying examples. Change in the position of the body with respect to time is known as Motion. The body is said to be in rest if the position of the body remains the same with respect to time. Each body moves in different paths with respect to time and external conditions.

Motion is classified into

- Linear motion
- Non-linear motion

The object that moves in a straight line is said to be in **Linear motion.**

If the movement of the object is not in a straight line with respect to time, it is known as **Non-linear motion.**

Depending on the path the body moves, the motion is classified into 4 types:

- Rotational motion
- Periodic motion
- Non-periodic motion
- Translatory motion

Let’s know about these motions in details with proper examples.

The movement of an object along the fixed axis or motion along the fixed axis is known as rotational motion.

**Example**: merry-go-round, rotating fan, windmill blades and many more

The motion which repeats after an equal or regular interval of time is known as Periodic motion.

**Example**: pendulum and hands of the clock.

The motion that does not repeat in the regular interval of time is known as non-periodic motion.

**Example**: driving a car, flying bird

The motion in which all particles of the body move the same distance at the same time is called Translatory motion.

**Example**: marching soldiers, moving animals in the herd and many more.

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