Materials

Question 1

Equation for density:

Answer 1

ρ=m/V

Where:
ρ is density in kgm^-3
m is mass in kg
V is volume in m^3

Question 2

When can the equation of density be applied?

Answer 2

For mixtures, pure substances and all states of matter.

Question 3

What procedure could you use to calculate the density of an irregularly shaped object?

Answer 3

First find the object’s mass then use a displacement vessel to find the volume of fluid displaced. This volume is equal to the volume of the object and from this you can use the density equation to calculate the object’s density.

Question 4

Define upthrust.

Answer 4

Upthrust equals weight of fluid displaced.

Question 5

Archimedes’ Principle:

Answer 5

When an object is submerged in a fluid, an upwards force called upthrust acts on the object.

Question 6

On a falling object what does weight equal (think of a free body diagram)?

Answer 6

W=R+U
R is viscous drag.
U is upthrust.

Question 7

Stoke’s Law equation:

Answer 7

F=6πrηv

Where:
F is viscous drag in N
r is the radius of the sphere in m
η is the coefficient of viscosity
v is velocity in ms^-1

Question 8

What assumptions does Stoke’s Law make?

Answer 8

It assumes that the object is small, spherical, travelling at a slow speed and with laminar flow.

Question 9

Describe laminar flow.

Answer 9

Streamlined with no mixing of layers.

Question 10

Describe turbulent flow.

Answer 10

Energy is dissipated with layers mixing and eddy currents.

Question 11

What factors affect the terminal velocity of an object?

Answer 11

Volume of the sphere.
Viscosity of fluid travelling through.
Density of fluid travelling through.
Density of solid.

Question 12

Hooke’s Law equation:

Answer 12

F=kl

Where:
F is force in N.
k is spring constant in N/m.
l is change in length in m.

Question 13

Hooke’s Law states that:

Answer 13

The force is directly proportional to the extension (or compression) of a material.

Question 14

What is the limit of proportionality?

Answer 14

Where the line on a force extension graph is no longer linear (proportional).

Question 15

What is the elastic limit on a force extension graph?

Answer 15

The point where plastic deformation occurs and the sample will not return to its original shape once the deforming force has been removed.

Question 16

What is the yield point on a force extension graph?

Answer 16

The point from where a little force added causes a large extension.

Question 17

What is the breaking point on a force extension graph?

Answer 17

The point where the line continues no further due to the sample breaking.

Question 18

What is elastic deformation?

Answer 18

Elastic deformation is where the material returns to its original shape once the deforming force has been removed.

Question 19

What is plastic deformation?

Answer 19

Plastic deformation is when the material does not return to its original shape once the deforming force has been removed.

Question 20

The steeper the gradient on a force extension graph the…

Answer 20

…greater the value of k and the stiffer the material making it more difficult to stretch.

Question 21

If we find the area under a force extension graph for the linear section what equation can we derive?

Answer 21

Eel = 1/2FΔx

Where:
Eel is elastic potential energy in J.
F is force in N.
Δx is extension or compression in m.

Question 22

Using Eel = 1/2FΔx and F = kΔx, what other equation can we derive by substitution?

Answer 22

Eel = 1/2kΔx^2

Where:
Eel is elastic potential energy in J.
k is the stiffness of the material in Nm^-1.
Δx is extension or compression in m.

Question 23

Factors that determine the deformation of a material caused by a force but aren’t considered in Hooke’s Law are:

Answer 23

Length

Cross Sectional Area

Question 24

Equation for stress:

Answer 24

σ=F/A

Where:
σ is stress in Nm^-2 or Pa.
F is force in N.
Area is cross sectional area in m^2.

Question 25

What is the strength of a material?

Answer 25

The stress at which it breaks. This could be tensile stress or compressive stress.

Question 26

Equation for strain:

Answer 26

ε=Δx/x

Where:
ε is stress.
x is original length.
Δx is change in length in the same unit as x.

Question 27

What is the unit for strain?

Answer 27

There isn’t a unit as it is just a ratio of length and change in length.

Question 28

If you plot a stress strain graph what is the gradient of linear section?

Answer 28

The gradient is the Young Modulus of that material.

Question 29

How can we find the Young Modulus of a material if we only know a stress and strain?

Answer 29

E = σ/ε

Where:
E is the Young Modulus in Pa.
σ is the stress in Pa.
ε is the strain.