Topic 4 - Materials - Spec Flashcards Preview

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Flashcards in Topic 4 - Materials - Spec Deck (26)
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1
Q

What is the Density Equation?

A

ρ = m / V ρ - Density (kg m*-3) m - Mass (kg) V - Volume (m*3)

2
Q

Define Upthrust?

A

Weight of Fluid Displaced Calculate the weight of the fluid an object displaces to calculate the Upthrust

3
Q

What is Stokes Law?

A

F = 6πaηv F - Viscous Drag (N) η - Viscosity of the fluid (Pas) r - Radius of the Object (m) v - speed of the object moving at terminal velocity (ms-1)

4
Q

What does the Stokes Law Equation only apply to?

A

Only applies too: - Small spherical objects - Moving At slow speeds - With Laminar Flow (absence of Turbulent Flow)

5
Q

What is Viscosity dependant upon?

A

Temperature

6
Q

What is the CORE PRACTICAL to determine the viscosity of a liquid?

A

1 - Fill a wide, clear tube with the liquid you want to investigate, know the density of the liquid 2 - Put a rubber band half way down the tube so that the ball bearing when it passes is at its terminal velocity 3 - Place two more elastic bands below the first, so that the distance between them is equal 4 - Measure the diameter and the radius of the ball bearing 5 - Drop ball into the tube, start stopwatch when the ball reaches the first band and record the time it reaches the other bands. 6 - Repeat three times. 7 - If the ball falls close to the walls re-do that test. 8 - Calculate the average time taken for each ball bearing to fall between the elastic bands, calculate the terminal velocity by using the average time and distance between bands. 9 - Calculate the viscosity of the liquid, using this equation… η = 2r²g(ρ-σ) / 9v η = Viscosity of the liquid r = Radius of the ball bearing g = gravitational field strength ρ = density of the ball bearing σ = Density of the liquid v = Terminal Velocity

7
Q

What is the Hooke’s Law?

A

F = kx F = Force (N) X = exetension (m) K = Spring Constant (N m*-1)

8
Q

What is the (Tensile or Compressive) Stress Equation?

A

Force / Cross Sectional Area

9
Q

What is the (Tensile or Compressive) Strain Equation?

A

Change in Length / Original Length

10
Q

What is Young’s Modulus Equation?

A

Stress / Strain

11
Q

What happens at the Elastic Limit Point?

A

Material starts to behave plastically, from this point the material would no longer return to its original shape.

12
Q

What happens at the Yield Point?

A

Here the material suddenly starts to stretch without any extra load. This is the point at which a large amount of plastic deformation takes place with a constant or reduced load.

13
Q

What happens at the Limit of Proportionality?

A
  • Occurs when the line is no longer straight and is bent. - At this point the material stops obeying Hooke’s Law - But would still Return to its original shape if the load was removed
14
Q

What does a happens with a Straight Line on a Stress Strain Graph?

A

A straight line through the origin shows the material IS OBEYING HOOKES LAW. - Gradient = Young’s Modulus

15
Q

A strong material has a…

A

High breaking stress

16
Q

Stiff materials are difficult to…

A

Stretch or Compress, they have a large Young’s Modulus

17
Q

Interpret Force-Extension and Force-Compression graphs.

A

Materials that are strong have a HIGH STRESS materials that are weak have a LOW STRESS

Materials that are Stiff have a SMALL STRAIN materials that are less stiff have a HIGH STRAIN.

18
Q

Where is the Limit of Proportionality on this graph?

A

Point P is the Limit of Proportionality

19
Q

Where is the Elastic Limit on this Stress / Strain Graph?

A

Point E on the Graph

20
Q

Where is the Yield Point on this Stress / Strain Graph.

A

Point Y on the graph is the Yield Point.

21
Q

Show the Elastic and Plastic Reigon on a Stress / Strain graph.

A
22
Q

What is meant by the term Breaking Stress?

A

When the stress becomes so great that atoms seperate completely and the material breaks.

23
Q

What is the UTS point on a Stress / Strain graph.

A

UTS (Ultimate Tensile Stress) the maximum stress that the material can withstand.

24
Q

CORE PRACTICAL - Find the Young Modulus, you need a very Long Wire.

A

1 - Set up the apparatus shown

2 - Test wire should be thin and as long as possible

3 - Find the cross-sectional area of the wire using a micrometer use the equation πr²

4 - Clamp the wire to the bench, start with a small weight to straighten the wire

5 - Measure the distance between the fixed end of the wire and the marker (unstretched length)

6 - By increasing the weight the wire stretches and the marker moves

7 - Increase the weight in equal steps, recording the marker each time, calculate the extension by subtracting the original length the the extended length

8 - Use the results from the experiment to calculate the stress and strain of the wire and plot a stress / strain curve.

25
Q

How do you calculate the elastic strain energy energy on a Stress / Strain Graph?

A

The area underneath the linear part of the stress - strain graph gives the strain energy

Energy per unit vol = 0.5 x stress x strain

  • If the line is not linear then you calculate the number of squares under the line and make an ESTIMATION.
26
Q
A