Materials

Question 1

What is density and what is its formula?

Answer 1

It is a measure of the compactness of an object.The formula is mass/volume. Density is in kg/m^3 or g/cm^3

Question 2

What is hooke’s law?

Answer 2

It states that the force applied to a wire is directly proportional to the extension of the wire.

Question 3

What is the formula for stress?

Answer 3

F/A. N/m^2

Question 4

What is the formula for strain?

Answer 4

Delta L/L.No units.

Question 5

What is the difference between a tensile and compressive force?

Answer 5

Tensile causes an extension, compressive compresses the material.

Question 6

What causes strain?

Answer 6

A stress.

Question 7

What is the breaking stress of a material?

Answer 7

It is the stress large enough to break the object?

Question 8

What is UTS?

Answer 8

It is the maximum stress the material can withstand without breaking.

Question 9

What is the area under a force extension graph?

Answer 9

It is the elastic potential energy stored in the stretched spring.Elastic strain energy.

Question 10

What is the formula for the elastic potential energy?

Answer 10

Epe=1/2xfxdelta l.

Question 11

What type of deformation is used in car design and how its it useful?

Answer 11

Plastic deformation is used.It is useful as some of the kinetic energy of the car is dissipated as it is used to deform the crumple zone.Therefore, less is transferred to the people inside.

Question 12

What is the formula for Young’s modulus?What are its units.

Answer 12

Stress/Strain. N/m^2.

Question 13

Describe an experiment to determine the young’s modulus of a wire.

Answer 13

Clamp one end of a wire in between 2 wooden block and pass the other end over a pulley.Attach a marker in between the ends and measure the length between the marker and the fixed end.This is the natural length.Add weights in 100g intervals and measure the distance between the marker and fixed end and minus from natural length to get your extension.Use a micrometer to measure the diameter of the wire.Then use pid^2/4 to find the cross sectional area.Plot a graph of stress/strain and find the gradient which is E.Use a long and thin wire to reduce uncertainty as it provides a large extension for a smaller force.

Question 14

What is the area under a stress strain curve?

Answer 14

It is equal to the energy stored per unit volume.You can calculate it up to the limit of proportionality.

Question 15

What is the effective spring constant of two springs in parallel?

Answer 15

K1+k2=effective K.

Question 16

What is the effective spring constant of two springs in series?

Answer 16

1/k1 +1/k2

Question 17

Describe a typical stress strain graph.

Answer 17

From 0 to the limit of proportionality stress and strain are directly proportional and the material is obeying hooke’s law.After this point the material does not obey hookes law and behaves elastically up to the elastic limit.After this point the material behaves plastically.Then there is the yield point where the wire weakens , the wire starts to stretch without any extra load.After the second yield point a small increase in stress causes a large increase in strain.The wire loses its strength becomes narrower at its UTS.

Question 18

What is the characteristic of a brittle material?I

Answer 18

It snaps suddenly without any plastic deformation.It obeys hookes law up to this point.

Question 19

What is the loading curve for a rubber?

Answer 19

It is elastic so the loading and unloading meet at the maxium and at zero.But the unloading curve is stretched more so it is under the loading curve.

Question 20

What is the loading curve for a metal?

Answer 20

It is the same if it is not stretched beyond its elastic limit.Otherwise the unloading curve is stretched to the right.

Question 21

What is the area between the loading and unloading curve?

Answer 21

Energy lost.Some energy becomes the energy of the internal energy of the molecules when unstrectched.

Question 22

What happens to the elastic strain energy when a material undergoes plastic deformation?

Answer 22

The energy is used to displace the molecules from their equilibrium positions permanently and change the shape of the material.