Ch6: Materials Flashcards
What is a tensile force?
A force that produces extension
What is a compressive force?
A force that shortens an object
What is the difference between tensile and compressive forces?
Compressive forces shorten an object while tensile forces extend an object
What happens when an object reaches it’s elastic limit?
It undergoes plastic deformation and will not return to its original length once the force is removed.
What happens to a spring when force is added before it’s elastic limit?
It undergoes elastic deformation and would return to original length if the force was removed.
What is Hooke’s law? And what is the limit for it?
Extension of a spring is directly proportional to the force applied to it. As long as it has not reached its elastic limit.
What is the equation for Hooke’s law? Define the terms.
F=kx
F: force
k: spring constant
x: extension/compression
How do you improve the accuracy of length measurements in the Hooke’s law experiment?
By taking readings at eye level with the point being measured.
What is the equation for elastic potential energy using force?
E=1/2Fx
How is the equation for Epe derived?
It is the area under a force/extension graph. Area=1/2 base x height
What is the equation for elastic potential energy using k? What is k?
E=1/2kx^2
k=spring constant
What happens to energy stored when extension is doubled?
It is quadrupled. Energy stored is proportional to extension^2
Do springs obey Hooke’s law?
Yes
Do rubber bands obey Hooke’s law?
No
What is represented by the gap in a force/extension graph of a rubber band?
The gap between the loading and unloading curves = thermal energy released by the process.
What is tensile stress?
Force applied per unit cross sectional area
What is the unit for tensile stress?
Pascals (force/area or N/m^-2)
What is the equation symbol for stress?
σ
What is tensile strain?
The fractional difference from the original length of a wire.
What is the equation for strain?
extension/original length
x/l
What is the equation symbol for strain?
ε
What is a ductile material?
A material that can be easily hammered or drawn into wire/thin sheets.
Stress is directly proportional to strain until what point?
The limit of proportionality
Does the limit of proportionality occur before or after the elastic limit?
Before
What is Young’s modulus?
The ratio of stress to strain.
How is Young’s modulus calculated?
Stress/strain or Fl/Ax
What is the unit for Young’s Modulus?
Pa or Nm^-2
A larger Young’s modulus means a material is more…
Stiff
What do stress/strain graphs look like for brittle materials?
Straight lines through the origin until breaking point.
What does a stress/strain graph look like for a rubber material?
Loading and Unloading curves similar to the force/extension graph for the same material.
How do you calculate the Spring Constant of multiple springs in Series?
1/Kt = 1/K1 + 1/K2 + 1/KN….
How do you calculate the Spring’s constant of multiple springs in parallel?
Kt = K1 + K2 + KN….
