materials

Question 1

extension

Answer 1

tensile forces act away from the centre of the spring in both directions and will stretch it out causing the spring to extend

Question 2

compression

Answer 2

forces act towards the centre of the spring in both directions causing compression

Question 3

what happens to spring when tensile/compressive forces are exerted

Answer 3

the spring undergoes tensile deformation or compressive deformation

Question 4

hookes law

Answer 4

force applied is directly proportional to the extension in length up to the limit of proportionality

Question 5

equation for hookes law

Answer 5

f = kx

Question 6

tensile stress

Answer 6

the force per unit area

Question 7

tensile strain

Answer 7

measure of how the material stretches, the extension divided by the original length, it has no units

Question 8

elastic deformation

Answer 8

who force is removed the object will return to its original shape

Question 9

plastic deformation

Answer 9

after force is removed the object will not return to its original shape - the limit of proportionality has been exceeded

Question 10

how is energy stored during elastic deformation

Answer 10

work done is transferred and stored as elastic potential energy

Question 11

describe energy changes that occur during plastic deformation

Answer 11

material is stretched and the energy from the work done is used to break the bonds between the molecules. this causes permanent deformation

Question 12

breaking stress

Answer 12

amount of stress a material can take without it breaking

Question 13

brittle material

Answer 13

it does not extend much when a force is applied (tensile strain stays low). the material tends to break rather than stretch under a large force

Question 14

elastic limit

Answer 14

the point after which plastic deformation occurs. it is sometimes also referred tons the limit of proportionality

Question 15

area underneath a force extension graph represent

Answer 15

energy stored in the material

Question 16

equation that calculates elastic strain energy in terms of spring constant and extension

Answer 16

E = 1/2kx^2

Question 17

Youngs modulus

Answer 17

tensile stress/ tensile strain

Question 18

how do you find Youngs modulus from a stress strain graph

Answer 18

gradient

Question 19

one method to determine Youngs models of a material in the form of a wire

Answer 19

• set up wire over a pulley attached to a clamp and attach a mass to the end of the wire
• place a ruler and maker under wire to measure distance travelled
• vary force, by varying mass and measure extension x
• measure the diameter of wire with micrometer
• take readings along he wire and average
• use this to calculate the cross sectional area
• measure original length with ruler
• measure extension x with a marker and ruler or with travelling microscope
• stress = force / cross sectional area
• strain = extension / original length
• Youngs modulus = stress / strain
• this is equal to the gradient from stress strain graph

Question 20

loading and unloading graph of metal wire

Answer 20

• metal wire obeys hookes law
• exhibits elastic deformation until elastic limit
• up to this point loading curve is the same as unloading
• beyond this point experiences plastic deformation
• unloading curve has the sae gradient as loading
• plastic deformation causes permanent deformation

Question 21

loading and unloading for rubber

Answer 21

• does not experience plastic deformation
• does not obey hookes law
• area between loading and unloading is the work done in stretching
• energy transferred to thermal when force is removed

Question 22

loading and unloading graph for polymeric material

Answer 22

• not obey hookes law
• experiences plastic deformation
• make new shapes but difficult to make original