Materials

Question 1

what is the density of a material

Answer 1

mass per unit volume

Question 2

what is hookes law

Answer 2

the extension is directly proportional to the force applied given that the environmental conditions are kept constant

Question 3

what is the limit of proportionality

Answer 3

is the point after hookes law is no longer obeyed

Question 4

what is the elastic limit

Answer 4

is when beyond this if you apply any more forces the object becomes plastically deformed

Question 5

what does the spring constant measure

Answer 5

the stiffness of the string

Question 6

what is tensile stress

Answer 6

force applied per unit cross sectional area

Question 7

what is tensile strain

Answer 7

this is the extension over the original length

Question 8

what is the energy stored as when work is done on a material to stretch or compress it

Answer 8

elastic strain energy

Question 9

what is breaking stress

Answer 9

is the value of stress at which the material will brak apart

Question 10

what can force-extension graphs show

Answer 10

the properties of a specific object

Question 11

what are the two main behaviors that a material can exhibit on a force-extension graph

Answer 11

plastic and brittle

Question 12

what is plastic behavior

Answer 12

this is where a material will experience a large amount of extension as the load is increased, especially beyond the elastic limit

Question 13

what is brittle behavior

Answer 13

this is where a material will extend very little, and therefore is likely to fracture at a low extension

Question 14

once a material is stretched beyond its elastic limit what will it show on a force extension graph

Answer 14

the unloading line will not return to the origin , however the loading and unloading lines will be parallel because the materials stiffness is constant

Question 15

what is the area between the loading and unloading line equal to

Answer 15

the work done to permanently deform the material

Question 16

when a stretch is elastic what is all the work done stored as

Answer 16

elastic strain energy

Question 17

what does elastic mean

Answer 17

a material will return to its original shape once the force applied is removed

Question 18

when a stretch is plastic work is done to do what and so what happens to the energy

Answer 18

to move the atoms apart and so the energy is dissipated as heat

Question 19

how is this fact used when designing safety features for cars

Answer 19

• work is done to deform crumple zones plastically to decrease the cars kinetic energy
• seat belts stretch in order to covert some of the passengers kinetic energy into elastic strain energy

Question 20

when a spring is hung vertically and stretched and then the force is removed what happens to the energy at different stages

Answer 20

• kinetic energy is converted into elastic strain energy when the spring is stretched
• when the force is removed the elastic stain energy will be transferred back to kinetic energy this kinetic energy is then transferred to gravitational potential energy

Question 21

what do stress-strain graphs describe

Answer 21

they describe the behavior of a material

Question 22

what is the ultimate tensile stress

Answer 22

the highest point on the gaph as it shows the maximum stress the material can withstand

Question 23

what can the shape of the line of a stress-strain show

Answer 23

whether the material is ductile, brittle or plastic

Question 24

what is ductile

Answer 24

can undergo a large amount of plastic deformation before fracturing

Question 25

what is the young modulus

Answer 25

is a value which describes the stiffness of a material

Question 26

is the value of young modulus constant

Answer 26

yes as when the material obeys hookes law the stress and strain of an object are proportional and therefore is constant

Question 27

what is the gradient of the stress-strain graph equal to

Answer 27

the young modulus