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A Level Physics > Materials > Flashcards

Flashcards in Materials Deck (29)
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1

Equation for density:

ρ=m/V

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

2

When can the equation of density be applied?

For mixtures, pure substances and all states of matter.

3

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

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.

4

Define upthrust.

Upthrust equals weight of fluid displaced.

5

Archimedes' Principle:

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

6

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

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

7

Stoke's Law equation:

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

8

What assumptions does Stoke's Law make?

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

9

Describe laminar flow.

Streamlined with no mixing of layers.

10

Describe turbulent flow.

Energy is dissipated with layers mixing and eddy currents.

11

What factors affect the terminal velocity of an object?

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

12

Hooke’s Law equation:

F=kl

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

13

Hooke’s Law states that:

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

14

What is the limit of proportionality?

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

15

What is the elastic limit on a force extension graph?

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

16

What is the yield point on a force extension graph?

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

17

What is the breaking point on a force extension graph?

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

18

What is elastic deformation?

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

19

What is plastic deformation?

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

20

The steeper the gradient on a force extension graph the...

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

21

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

Eel = 1/2FΔx

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

22

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

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.

23

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

Length
Cross Sectional Area

24

Equation for stress:

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.

25

What is the strength of a material?

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

26

Equation for strain:

ε=Δx/x

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

27

What is the unit for strain?

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

28

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

The gradient is the Young Modulus of that material.

29

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

E = σ/ε

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