Materials

Question 1

Upthrust

Answer 1

The upward force exerted on an object by the fluid it is immersed in.

Question 2

Archimedes principle

Answer 2

Upthrust is equal to the weight of the fluid displaced

Question 3

Pressure of fluid at depth

Answer 3

Depth x density x g

Question 4

Laminar flow

Answer 4

Streamlines are parallel and constant. No crossing / abrupt changes

Question 5

Turbulent flow

Answer 5

Streamlines frequently cross. They form vortices. Non continuous and constantly changing.

Question 6

Laminar flow occurs when

Answer 6

The rate of flow is below a critical point

Question 7

Turbulent flow occurs when

Answer 7

The rate of flow is above a critical point or an object is obstructing or moving through the liquid.

Question 8

Viscosity

Answer 8

An internal friction present between two layers of a liquid which resists the flow of the liquid. The higher the viscosity, the harder it is for a fluid to flow, so it flows slower.

Question 9

Stoke’s law

Answer 9

F = 6πηrv.
Where :
F = Drag in Newtons
η = coefficient of viscosity in pascal seconds
r = radius of ball bearing in metres
V = velocity of ball bearing in ms^-1

Question 10

Conditions for Stoke’s law to be valid

Answer 10

• Object must be solid, smooth and spherical
• Object must be of uniform density
• Object must be sufficiently large compared to fluid molecules
• The fluid must have laminar flow around the object
• The fluid must be homogenous

Question 11

Rubber bands under stress

Answer 11

• Rubber bands are made from polymer chains. At rest, the chains are tangled and knotted which requires force to undo.
• Eventually, the chains become un-knotted, and the force required to stretch the rubber band decreases.
• However, when stretched enough the chains become taught and the rubber band becomes stiffer again as you are pulling against molecular forces.

Question 12

Stress

Answer 12

The force applied per unit cross sectional area.
= Force / Cross sectional area = F / A
Units : NM^-2
Sometimes presented as σ (sigma)

Question 13

Strain

Answer 13

The change in length divided by the original length
= Change in length / original length = ∆L / L
Units : None. m/m = pure number
Sometimes presented as ε (epsilon)

Question 14

Breaking stress

Answer 14

The amount of stress required to break a material
If a stress-strain curve stops, the material has broken.

Question 15

Young Modulus

Answer 15

The ratio of tensile stress to tensile strain.
Equation: E = Fl / AΔl
Units: Pa
Tells us how easily a material can stretch and deform

Question 16

The gradient of a stress strain graph

Answer 16

The young modulus of the material

Question 17

The area under the stress strain graph

Answer 17

The energy stored per unit volume in the material

Question 18

Tough

Answer 18

A material capable of absorbing lots of energy before breaking

Question 19

Strong

Answer 19

A material can withstand a large applied force before breaking

Question 20

Stiff

Answer 20

A material resists deformation in response to applied forces