Materials

Question 1

What is Hooke’s Law?

Answer 1

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

Question 2

What is the equation for Hooke’s law?

Answer 2

F=ke

Question 3

What is density?

Answer 3

Density is a measure of the compactness of a substance

also defined as its mass per unit volume

Question 4

What is the equation for density?

Answer 4

Density(kgm^-3) = mass(kg) / volume(m^3)

Question 5

How can we find out which substance is denser as we compare two substances?

Answer 5

The substance with the greater mass in the same volume is denser than the other.

Question 6

How can the density of a regular solid be measure?

Answer 6

• measure its mass using a top-pan balance
• measure the dimensions using vernier callipers and calculate its volume using the appropriate equation
• calculate the density

Question 7

How can the density of a liquid be measured?

Answer 7

• measure the mass of an empty measuring cylinder
• pour the liquid into the measuring cylinder and measure the volume directly
• measure the mass of the cylinder and liquid to calculate the mass of the liquid
• calculate the density

Question 8

How can the density of an irregular solid be measured?

Answer 8

• measure the mass of an object
• Immerse the object in a liquid in a measuring cylinder or beaker and observe the increase in liquid level-this is the volume of the object
• calculate the density

Question 9

What is an alloy?

Answer 9

An alloy is a solid mixture of two or more metals.

Question 10

How do you find out the volume of a cuboid?

Answer 10

volume = abc

Question 11

How do you find out the volume of a cylinder?

Answer 11

volume = (pi*diameter^2 )/ 4 * height

Question 12

What happens when a spring is stretched?

Answer 12

The stretched spring exerts a pull(tension) on the object holding each end of the spring

Question 13

What is the elastic limit?

Answer 13

This is the maximum force that can be applied onto a material and still regain its original shape.

Question 14

What is the standard form of measurement units from Giga to picto?

Answer 14

G(billion)-1*10^9
M(million)-1*10^6
K(thousand)-1*10^3
cm-1*10^-2
mm-1*10^-3
µ(micro)-1*10^-6
n(nano)-1*10^-9
p(picto)-1*10^-12

Question 15

What are tensile forces?

Answer 15

Stretching forces

Question 16

What are compressive forces?

Answer 16

Squashing forces

Question 17

What are shear forces?

Answer 17

Cutting forces which change the area of the object

Question 18

What are torsional forces?

Answer 18

Twisting forces which change the area of the object

Question 19

What happens to the extension when the springs are in parallel?

Answer 19

The extension halves as they are sharing the force and only half the force is applied to each spring.

Question 20

What happens to the extension when the springs are in series?

Answer 20

The extension doubles because the same force is being applied to each spring.

Question 21

What is elasticity?

Answer 21

The property of a solid that enables it to regain its original shape after the force is removed

Question 22

What is plasticity?

Answer 22

This describes the deformation of a material after the elastic limit is exceeded. The material can longer regain its original shape once it is plastically deformed

Question 23

What is stiffness?

Answer 23

This is the measurement of a material’s resistance to changes in size or shape. Also known as the spring constant.

Question 24

What is ductility?

Answer 24

The ability for a material to easily stretch without breaking.

Question 25

What is brittleness?

Answer 25

It is the ability for a material to snap without stretching or bending when subjected to stress and the elastic limit is exceeded.

Question 26

What happens to the energy that is used to stretch a spring?

Answer 26

The energy is stored as elastic potential energy

Question 27

How can you calculate the energy stored in a stretched spring?

Answer 27

Energy= (force*extension)/2 or Energy = (spring constant*extension^2)/2

Question 28

What is the equation for stress?

Answer 28

stress = force/cross-sectional area

Question 29

What is the equation for strain?

Answer 29

strain = extension/original length

Question 30

Why does strain have no unit?

Answer 30

It is a ratio

Question 31

What is the Young Modulus?

Answer 31

It is a constant value of a material | Measured in Nm^-2(the unit of stress)

Question 32

What is the equation for the Young Modulus?

Answer 32

Young Modulus = tensile stress/tensile strain

Question 33

What happens at the yield point on a stress/strain graph?

Answer 33

The material stretches without any extra load | The yield point is the stress at which a large amount of plastic deformation takes place with a constant or reduced load

Question 34

What happens at the elastic limit?

Answer 34

The material starts to behave plastically | from this point onwards, the material would no longer return to its original shape once the stress is removed.

Question 35

What happens at the limit of proportionality?

Answer 35

The material stops obeying Hooke's law but would still return to its original shape if the stress is removed

Question 36

What happens to brittle items when the stress applied reaches the elastic limit?

Answer 36

The material fractures and doesn't behave plastically

Question 37

Give examples of brittle items

Answer 37

Ceramics glass Nylon

Question 38

How can you calculate the Young modulus from a stress/strain graph?

Answer 38

The constant gradient, where the material obey's Hooke's law, is the young modulus of the material

Question 39

Why is the unloading line parallel to the loading line?

Answer 39

The stiffness constant,k, is the same

Question 40

Why doesn't the unloading curve return to the origin?

Answer 40

The wire was stretched beyond its elastic limit and deformed plastically it has been permanently stretched

Question 41

How can you calculate the work done to permanently deform the wire?

Answer 41

energy stored + heat lost = total work done

Question 42

What is the ultimate tensile stress?

Answer 42

This is the maximum stress that the material can withstand

Question 43

What is the breaking stress?

Answer 43

The stress that causes the atoms to completely separate and the material breaks

Question 44

When does elastic deformation happen?

Answer 44

Before the elastic limit is reached

Question 45

When does plastic deformation happen?

Answer 45

When the elastic limit is exceeded

Question 46

What happens during elastic deformation?

Answer 46

- the atoms of the material are pulled apart when the material is under tension - atoms move small distances without changing positions in the material - once the load is removed, the atoms return to their original distance apart

Question 47

What happens during plastic deformation?

Answer 47

- some atoms in the material move position relative to one another - when the load is removed, the atoms don't return to their original positions

Question 48

How can you calculate the strain energy?

Answer 48

(stress*strain)/2 OR (force *extension/area*length)/2

Question 49

What happens beyond the elastic limit?

Answer 49

Some of the energy that caused the plastic deformation cannot be regained and is transformed into thermal energy

Question 50

How can you tell if a material is ductile or not from a stress/strain graph?

Answer 50

Ductile materials have yield points and a large extension is produced when a small amount of extra stress is added

Question 51

How can you calculate the work done from stress/strain graphs?

Answer 51

The area between the loading and unloading curves is the work done to permanently stretch the material

Question 52

How can the Young's Modulus of a metal wire be obtained accurately from an experiment?

Answer 52

Measurements of the metal wire -the original length of the wire -the diameter of the wire -the extension each time a force is added(increase the force in steps e.g 100g weights intervals Accuracy of results -repeat readings -measure the diameter of the wire in several places and calculate the average Plot the results on a stress/strain graph calculate the gradient (the Young's Modulus)