Physics 10: Elasticity and Hooke's Law

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Questions and Answers

What is elasticity?

Elasticity is the ability of a substance to regain its original shape and size after being distorted by an external force.

What is an elastic material?

An elastic material is one that regains its original shape and size after the distorting external force has been removed.

State Hooke's law.

Hooke's law states that, provided the elastic limit of an elastic material is not exceeded, the extension, e, of the material is directly proportional to the applied force, F.

The mathematical expression for Hooke's law is ______ where k is the constant of proportionality called elastic constant, force constant, or stiffness of the material.

F = ke Signup and view all the answers

What is the definition of the elastic constant or stiffness of an elastic material?

The elastic constant or stiffness of an elastic material is the force required to produce unit extension of the material. Signup and view all the answers

The working of a spring balance is based on Hooke's law.

True Signup and view all the answers

What is meant by the 'proportionality limit' in the context of an elastic material?

The proportionality limit (P) is the point up to which the extension of the material is directly proportional to the applied load. Signup and view all the answers

What is meant by the 'elastic limit' in the context of an elastic material?

The elastic limit (E) is the point beyond which the material will not return to its original length if the applied force is removed, even if the force is removed. Signup and view all the answers

What is the definition of the yield point in the context of an elastic material?

The yield point (Y) is the point where the material starts to deform permanently and loses its elasticity, and it marks the beginning of the 'plastic region'. Signup and view all the answers

What is meant by the 'breaking point' in the context of an elastic material?

The breaking point (B) is the maximum extension that can be produced in the material before it breaks or fractures. Signup and view all the answers

What is stress?

Stress is defined as the ratio of the force applied to the cross-sectional area of the elastic material. Signup and view all the answers

What is Young's modulus?

Young's modulus is a material property that represents the stiffness or resistance of a material to elastic deformation under tensile or compressive stress. Signup and view all the answers

What is the unit of Young's modulus?

The unit of Young's modulus is N/m² (Newton per square meter), which is the same unit as stress. Signup and view all the answers

What is bulk modulus?

Bulk modulus is a measure of a material's resistance to compression or volume change under hydrostatic pressure. Signup and view all the answers

What is the inverse of bulk modulus?

The inverse of bulk modulus is known as 'compressibility,' which indicates how easily a material can be compressed. Signup and view all the answers

What is the definition of elastic potential energy?

The elastic potential energy of a stretched or compressed material is the ability of the material to do work. Signup and view all the answers

How is elastic potential energy calculated?

The elastic potential energy (U) is calculated using the formula U = 1/2 k e² where k is the force constant (spring constant) and e is the extension or compression of the material. Signup and view all the answers

Give some applications of elasticity.

Elasticity plays a crucial role in various applications, such as the design of springs, rubber bands, blood vessels, medical devices (stethoscopes, blood pressure cuffs, catheters), and wound care materials. Signup and view all the answers

What is the significance of elastic potential energy in catapults?

In catapults, the elastic potential energy stored in the stretched rubber band or spring is converted into kinetic energy of the projectile when it is released. Signup and view all the answers

Study Notes

Elasticity in Solids

Solids change shape or size under force, but return to original state if force removed. This is elasticity.
Elastic materials regain original shape/size after the force is removed.
Hooke's Law states that extension (e) of an elastic material is directly proportional to the applied force (F) if the elastic limit is not exceeded.
Mathematically: F = ke, where 'k' is the elastic constant (force constant/stiffness). 'k' is the force needed to produce unit extension of the material. Units are Newtons per metre (Nm⁻¹).

Hooke's Law Verification

Experimental setup involves a spring, scale pan, pointer, weights and a scale.
Add weights in equal steps. Record pointer readings for each instance, calculating the total load on the spring (load on the pan + pan weight).
Remove weights, record pointer readings.
Record all readings (increasing and decreasing load) and calculate average readings.
Plot a graph of extension vs load.
A straight line graph through the origin verifies Hooke's Law (extension is directly proportional to load).

Elastic Limit

It is the maximum force a material can withstand before losing its ability to return to its original shape.
The region of the graph from the origin up until the proportionality limit, P is called the elastic region.
Beyond the elastic limit (E) the material is permanently deformed.
Beyond the elastic limit the material is said to have entered the plastic region. At the yield point the material yields or loses all elasticity permanently.

Yield Point

The point beyond the elastic limit where the material has yielded all its elasticity and becomes plastic.
In this region, a sudden, rapid increase in extension occurs for a slight increase in load.

Young's Modulus of Elasticity

Ratio of tensile stress to tensile strain.
A measure of the stiffness of a material.
Formula: Y = (F/A) / (e/L), where F is force, A is cross-sectional area, e is extension and L is original length.
Units: Nm⁻².

Work Done in Springs

Work done in stretching/compressing a spring = 1/2ke².
This work is stored as potential energy in the material.
When the force is removed, the material regains its original length, releasing the stored energy.

Elastic Potential Energy

Ability of a stretched/compressed material to do work.
Given by 1/2Fe or 1/2ke².
In applications such as catapults, the stored elastic potential energy is converted to kinetic energy in the projectile .

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Description

Explore the fascinating world of elasticity in solids and the principles of Hooke's Law through this quiz. Understand how materials respond to forces and verify the law experimentally. Test your knowledge on elastic constants, experimental setups, and graphing results.