Deck 8: Chapter 4 definitions Flashcards
Hooke’s law
The force needed to extend or compress a spring by some distance is proportional to that distance.
What are the units of stress?
Nm^-2 also known as pascal, pa for short.
What is the equation for stress?
Force ______ area
What are the several types of stress?
Tension(stretching),compression,torsion(twisting)
Unit for strength?
Pa
What is the definition for strong?
A large stress is needed to cause failure.
What is the definition for strength?
The maximum stress a material can withstand before failure.
What is the definition for weak?
Little stress needed to cause failure.
What are the units for toughness?
J/m^2
What is toughness?
1)Needs a large amount of energy to break it.2)Undergoes a large amount of plastic deformation before breaking.3)Resists crack propagation.
What is toughness defined as strictly?
1)The energy required to create a new surface area,units are J/m^22)The energy absorbed per unit volume,units are j/m^3
What is a brittle materials?
Does not undergo much plastic deformation, the break soon after elastic limit.2)Cracks pass easily through the material and fracture tends to be sudden and catastrophic.However,brittle materials can strong.
What are hard materials?
Materials that are resistive to dents or scratches.Units are Pa
What is the definition of elastic?
Changes shape when stress is applied but returns to its original shape when stress removed.
What is the definition of plastic?
Does not return to its original shape after deformation. Plastic deformation is a permanent change of shape.
What is meant by ductile?
Can be easily drawn into a wire.
What is meant by malleable?
Can easily be hammered or pressed into shape.
What is Stress defined as?
Defined as the force per unit area acting perpendicular to the area.Stress is also said to be a measure of how strong a material is?
definition of strain
Defined as the change per unit length.Strain is a ratio so there’s no unit.Stress causes strain.Putting pressure on an object causes it to stretch.Strain is a measure of how much an object is being stretched.
Equation for strain is?
extension/original length
define young modulus
When a material undergoes stress,provided the limit of proportionality is not exceeded, the value of stress/strain is constant this value is known as the young modulus of elasticity of the material.
What is the young modulus equation?
E=Stress/strain
define elastic.
The young modulus is constant,so the material is obeying hookes law. So after the stress stops the material will go back to its original shape.
what is yield?
The point at which the metal becomes permanently deformed.
What is UTS?
Ultimate tensile strength is the maximum stress that a material can withstand while being stretched or pulled before failing or breaking.
What is the yield strength?
The stress at which an elastic material under increasing stress ceases to behave elastically.
what is stiffness defined as?
The measure of the difficulty of stretching or bending an object.
What happens when light enters glass?
Light slows down when it enters glass and speeds up again as it leaves. The wave fronts are closer together in glass than in air.
How do you work out the refractive index of glass?
Speed of light in a vacuum / speed of light in glass.
What is the speed of light in a vacuum?
3 x 10^8 m/s
How can you make glass invisible? and explain why?
If you immerse glass in some clear oil, if the oil and glass have the same refractive index,the glass will be virtually invisible. This is because the two refractive indexes
