11 Materials

Question 1

what is density?

Answer 1

mass per unit volume

Question 2

how do you measure the density of a regular solid?

Answer 2

• mass - top pan balance
• measure dimensions using vernier calipers/micrometer + calculate volume

Question 3

how do you work out the density of a liquid?

Answer 3

• mass - measure mass of an empty measuring cylinder. pour some of the liquid into the cylinder measure mass again with the cylinder + liquid. mass = total - cylinder
• volume - measure volume directly from cylinder

Question 4

how do you measure the density of an irregular solid?

Answer 4

• mass - balance
• immerse object on a thread in liquid in measuring cylinder. observe increase in liquid level. this is volume

Question 5

what is an alloy?

Answer 5

a mixture of two metals

Question 6

how do you calculate the density of an alloy?

Answer 6

𝜌 = (𝜌₁V₁ + 𝜌₂V₂) / V

Question 7

what is Hooke’s law?

Answer 7

the force needed to stretch a spring is directly proportional to the extension of the string from its natural length

Question 8

what is the formula for Hooke’s law?

Answer 8

F = kΔL

Question 9

What is a spring’s elastic limit?

Answer 9

point beyond which a wire is permanently stretched

Question 10

What is the same for springs which are stretched in parallel?

Answer 10

The extension is the same for each spring

Question 11

What is the same for springs which are stretched in series?

Answer 11

The tension in each spring is the same which is equal to the weight W

Question 12

From a force/extension graph, how is the energy stored in a stretched spring calculated?

Answer 12

Area under the graph
E = 1/2 ⨉ F ⨉ ΔL = 1/2 ⨉ k ⨉ ΔL²

Question 13

What is elasticity?

Answer 13

Of a solid material
ability to regain its shape after it has been deformed/distorted and the forces that deformed it have been released

Question 14

what is the deformation that stretches called?

Answer 14

tensile

Question 15

what are deformations that compresses called?

Answer 15

compressive

Question 16

what is tensile stress?

Answer 16

force per unit area of cross section in a solid perpendicular to the cross section

Question 17

what is tensile strain?

Answer 17

extension per unit length of a solid when deformed

Question 18

What is the Young modulus?

Answer 18

the constant value of stress/strain for a material

Question 19

what is the yield point of a material?

Answer 19

the point at which the stress in a wire suddenly drops when the wire is subjected to increasing strain

Question 20

what is plastic deformation?

Answer 20

the deformation of a solid beyond its elastic limit

Question 21

What is ultimate tensile stress?

Answer 21

tensile stress needed to break a solid material
also known as breaking stress

Question 22

what is the stiffness of a material related to on a stress strain graph?

Answer 22

the gradient of the stress strain line which is equal to the Young modulus

Question 23

what is the strength of a material?

Answer 23

the ultimate tensile stress of the material

Question 24

what does brittle mean?

Answer 24

snaps without stretching or bending when subject to stress

Question 25

what does ductile mean?

Answer 25

stretches easily without breaking

Question 26

what do the loading and unloading curves of a metal wire look like?

Answer 26

they are the same provided its elastic limit is not exceeded ∴ returns to its original length.
if the elastic limit is exceeded, the unloading line is parallel to the loading line

Question 27

what do the loading and unloading curves of a rubber band look like?

Answer 27

• returns to the same unstretched length
• unloading curve is below the loading curve except at zero and maximum extensions

Question 28

what do the loading and unloading curves of a polythene strip look like?

Answer 28

• the extension during unloading is greater than during loading.
• the strip does not return to the same initial length
• suffers plastic deformation

Question 29

what is strain energy?

Answer 29

the work done to deform an object

Question 30

what is the formula for the elastic energy stored in a stretched wire and where is it derived from?

Answer 30

1/2 T ΔL
from the area under a force extension graph