Materials Flashcards
What is Hooke’s Law?
The extension is directly proportional to the force applied up to the limit of proportionality
What is the equation for Hooke’s law?
F=ke
What is density?
Density is a measure of the compactness of a substance
also defined as its mass per unit volume
What is the equation for density?
Density(kgm^-3) = mass(kg) / volume(m^3)
How can we find out which substance is denser as we compare two substances?
The substance with the greater mass in the same volume is denser than the other.
How can the density of a regular solid be measure?
- measure its mass using a top-pan balance
- measure the dimensions using vernier callipers and calculate its volume using the appropriate equation
- calculate the density
How can the density of a liquid be measured?
- measure the mass of an empty measuring cylinder
- pour the liquid into the measuring cylinder and measure the volume directly
- measure the mass of the cylinder and liquid to calculate the mass of the liquid
- calculate the density
How can the density of an irregular solid be measured?
- measure the mass of an object
- Immerse the object in a liquid in a measuring cylinder or beaker and observe the increase in liquid level-this is the volume of the object
- calculate the density
What is an alloy?
An alloy is a solid mixture of two or more metals.
How do you find out the volume of a cuboid?
volume = abc
How do you find out the volume of a cylinder?
volume = (pi*diameter^2 )/ 4 * height
What happens when a spring is stretched?
The stretched spring exerts a pull(tension) on the object holding each end of the spring
What is the elastic limit?
This is the maximum force that can be applied onto a material and still regain its original shape.
What is the standard form of measurement units from Giga to picto?
G(billion)-1*10^9 M(million)-1*10^6 K(thousand)-1*10^3 cm-1*10^-2 mm-1*10^-3 µ(micro)-1*10^-6 n(nano)-1*10^-9 p(picto)-1*10^-12
What are tensile forces?
Stretching forces
What are compressive forces?
Squashing forces
What are shear forces?
Cutting forces which change the area of the object
What are torsional forces?
Twisting forces which change the area of the object
What happens to the extension when the springs are in parallel?
The extension halves as they are sharing the force and only half the force is applied to each spring.
What happens to the extension when the springs are in series?
The extension doubles because the same force is being applied to each spring.
What is elasticity?
The property of a solid that enables it to regain its original shape after the force is removed
What is plasticity?
This describes the deformation of a material after the elastic limit is exceeded. The material can longer regain its original shape once it is plastically deformed
What is stiffness?
This is the measurement of a material’s resistance to changes in size or shape. Also known as the spring constant.
What is ductility?
The ability for a material to easily stretch without breaking.
What is brittleness?
It is the ability for a material to snap without stretching or bending when subjected to stress and the elastic limit is exceeded.
What happens to the energy that is used to stretch a spring?
The energy is stored as elastic potential energy
How can you calculate the energy stored in a stretched spring?
Energy= (forceextension)/2
or
Energy = (spring constantextension^2)/2
What is the equation for stress?
stress = force/cross-sectional area
What is the equation for strain?
strain = extension/original length
Why does strain have no unit?
It is a ratio
What is the Young Modulus?
It is a constant value of a material
Measured in Nm^-2(the unit of stress)
What is the equation for the Young Modulus?
Young Modulus = tensile stress/tensile strain
What happens at the yield point on a stress/strain graph?
The material stretches without any extra load
The yield point is the stress at which a large amount of plastic deformation takes place with a constant or reduced load
What happens at the elastic limit?
The material starts to behave plastically
from this point onwards, the material would no longer return to its original shape once the stress is removed.
What happens at the limit of proportionality?
The material stops obeying Hooke’s law but would still return to its original shape if the stress is removed
What happens to brittle items when the stress applied reaches the elastic limit?
The material fractures and doesn’t behave plastically
Give examples of brittle items
Ceramics
glass
Nylon
How can you calculate the Young modulus from a stress/strain graph?
The constant gradient, where the material obey’s Hooke’s law, is the young modulus of the material
Why is the unloading line parallel to the loading line?
The stiffness constant,k, is the same
Why doesn’t the unloading curve return to the origin?
The wire was stretched beyond its elastic limit and deformed plastically
it has been permanently stretched
How can you calculate the work done to permanently deform the wire?
energy stored + heat lost = total work done
What is the ultimate tensile stress?
This is the maximum stress that the material can withstand
What is the breaking stress?
The stress that causes the atoms to completely separate and the material breaks
When does elastic deformation happen?
Before the elastic limit is reached
When does plastic deformation happen?
When the elastic limit is exceeded
What happens during elastic deformation?
- the atoms of the material are pulled apart when the material is under tension
- atoms move small distances without changing positions in the material
- once the load is removed, the atoms return to their original distance apart
What happens during plastic deformation?
- some atoms in the material move position relative to one another
- when the load is removed, the atoms don’t return to their original positions
How can you calculate the strain energy?
(stress*strain)/2
OR
(force extension/arealength)/2
What happens beyond the elastic limit?
Some of the energy that caused the plastic deformation cannot be regained and is transformed into thermal energy
How can you tell if a material is ductile or not from a stress/strain graph?
Ductile materials have yield points and a large extension is produced when a small amount of extra stress is added
How can you calculate the work done from stress/strain graphs?
The area between the loading and unloading curves is the work done to permanently stretch the material
How can the Young’s Modulus of a metal wire be obtained accurately from an experiment?
Measurements of the metal wire
-the original length of the wire
-the diameter of the wire
-the extension each time a force is added(increase the force in steps e.g 100g weights intervals
Accuracy of results
-repeat readings
-measure the diameter of the wire in several places and calculate the average
Plot the results on a stress/strain graph
calculate the gradient (the Young’s Modulus)
