6) materials Flashcards
state hookes law?
the extension of a spring is directly proportional to the force applied providing the limit of proportionality is not exceeded
what is the formula for force that includes extension?
F=kx
what does the force constant measure?
the stiffness of a spring
what is elastic deformation?
once force is removed, it goes back to original length
what is plastic deformation?
once force is removed, there is permanent structural damage so doesn’t go back to original length
what is the elastic limit?
elastic limit is maximum extension for which plastic deformation does not occur
what shows the work done on a force extension graph?
the area under the graph
what is formula for work done?
0.5 x force x extension
or
0.5 x K x (extension)^2
explain an experiment for hooke’s law?
1- attach spring with boss and clamp to a bench using g clamp
2- set up a meter ruler with resolution 1mm close to
spring
3- suspend slotted masses from spring and as u
measure each one, measure new total mass and
height
4- gradient equal force constant and will be directly
proportional
5- evaluation: measure mass with digital scale, 6 readings
then average for most accurate result
what is the relationship between energy and extension?
energy is directly proportional to extension^2
what does a force extension graph for rubber show?
does not obey hookes law
elastic deformation
more work done is needed to extend it then return it
what does a force extension graph for polythene show?
doesn’t obey hookes law
more work is done to extend it
plastic deformation
what is the formula for tensile stress?
force/ cross sectional area
what is the formula for tensile strain?
extension/original length
what is the formula for young modulus?
tensile stress /tensile strain
what is the young modulus of a stress- strain graph?
the gradient of the linear section
`what is the relationship between tensile stress of material and strength?
the larger the tensile stress the stronger the material
determining young modulus of the wire experiment?
attach a 2m wire on one end over a pulley, wear eye protection in case wire snaps. measure diameter of wire using micrometre, record multiple values then take an average. area= pi x diameter^2 / 4. force is measured by mass x gravity. after adding mass, measure extension of wire with ruler.
what occurs to the spring constant when two identical springs are attached in series and why?
it halves, as the force remains same but as two springs extension doubles. force= k x extension
What is a brittle material?
A material that show only elastic behavior up to its breaking point, without plastically deforming.
What is a polymeric material?
A material made from long chain molecules.
what is a ductile material?
A material which can be drawn into a wire or hammered into thin sheets.
What is the yield point of a material?
The point at which the material starts to extend rapidly as stress increases.
What is the ultimate tensile strength of a material?
The maximum stress a material can withstand before breaking.
When does the Young Modulus apply to a material?
When stress is proportional to strain OR when it is obeying Hooke’s law
What is a tensile force?
A force produces an extension of the object.
What is a compressive force?
A force that reduces the length of an object.
