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EGR 1301 > Mechanics And Fluids > Flashcards

Mechanics And Fluids Flashcards

0
Q

Newton’s first law

A

A body at rest or in constant motion remains in that state until acted upon by an external unopposed force

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1
Q

Mechanics

A

The study of objects at rest or in motion and the effects of forces on a body

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2
Q

Newton’s second law

A

An unopposed forces causes a mass to accelerate

ΣF= ma

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3
Q

Newton’s third law

A

Every force has an equal and opposite reaction

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4
Q

Two divisions of mechanics

A

Statics

Dynamics

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5
Q

In statics, ΣF….

A

ΣF= 0

Because a=0

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6
Q

Statics is the study of…

A

Of forces acting on a non-accelerating body

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7
Q

Dynamics is the study of…

A

Motion of a body, both in translation and rotation

So ΣF cant be 0

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8
Q

Types of loading

A
  1. Tension: pull apart
  2. Compression: push together
  3. Moment: rotation
  4. Shear: distort shape
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9
Q

Scalar

A

Only has magnitude

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10
Q

Vector

A

Has magnitude and direction

Can be broken into x and y components

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11
Q

Adding vectors

A 
Cx= Ax+Bx
Cy= Ay+By
C= sqrt(Cx^2 + Cy^2)
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12
Q

Multiplying vectors

A

Can only be multiplied by a scalar
Changes the vector’s magnitude
Does NOT change the vector’s diction
No negative numbers for the test

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13
Q

Unit vectors

A

i has magnitude of 1 in x direction

j has magnitude of 1 in y direction

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14
Q

When a vector component is multiplied by i or j

A

Magnitude of vector component is unchanged
The direction of the vector com pone is defined as parallel to the x or y axis
ΣF= Fxi + Fyj

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15
Q

When drawing FBDs

A
  1. Forces are detached from ground and other bodies
  2. All external forces are indicated (weight is applied at center of gravity)
  3. Indicate magnitude and direction of known external forces
  4. Include dimensions
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16
Q

Reaction forces in rollers/rockers

A

Perpendicular to the roller/rocker

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17
Q

Reaction forces in pins

A

Have x and y components

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18
Q

Truss

A

A simple skeletal structure (made of triangles

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19
Q

In theory, the individual members of a simple true are only subject to…

A

Tension (pulling) and compression (pushing)

No bending forces

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20
Q

Why structures are built with triangles

A
  1. Pinned triangles are naturally rigid
  2. Joint strength becomes less critical
  3. High stiffness can be achieved for small amount of material used
  4. Ease of construction
21
Q

Members in tension

A

Tension forces tend to pull the member apart
Member tends to “stretch”
More economical
Can be made lighter/thinner

22
Q

Members in compression

A

Compressive forces tend to “squeeze” the member
Long slender members tend to buckle easily and can only carry smaller loads
Shorter members can carry higher compressive loads

23
Q

Assumptions for static analysis of truss bridges

A
  1. ΣF at each joint (node) must equal zero
  2. Each element is a “two force” member.
    Tension: ⬅️➖➡️
    Compression: ➡️➖⬅️
  3. Joints are pinned and frictionless (pins will not support a moment)
  4. Forces can only be applied at joints (no bending)
  5. No deformation occurs to change dimensions
  6. External reactions are statically determinant, and supports are frictionless
24
Q

Solving for trusses by method of joints

A
  1. Draw FBD and determine reactions at supports
  2. Locate joint with 2 members and draw FBD of that pin. Determine unknown forces at the joint
  3. Locate a member where forces in only 2 members is still unknown. Draw FBD and solve
  4. Repeat
25
Q

Joints under special loading conditions:

Forces in opposite member interesting 2 straight lines at a joint are….

A

Equal

26
Q

Joints under special loading conditions:

The forces in two opposite members are equal when….

A

A load is aligned with a third member.

The third member force is equal to the load (including zero load)

27
Q

Joints under special loading conditions:

The forces in 2 members connected at a joint are equal if…

A

The members are aligned and zero otherwise

28
Q

Why learn about joints under special loading conditions?

A

Simplifies truss analyses

29
Q

What is fluid mechanics?

A

Sumptuary of fluids in motion

30
Q

Two classes of fluids

A

Liquids

Gases

31
Q

Unlike solids, fluids can’t…

A

Resist shear stress

Assume the shape of containers

32
Q

Pressure

A

Force per area
P= F/A
Fluid exerts a force perpendicular to a surface
THERE IS NO PARALLEL COMPONENT THAT WOULD CAUSE A FLUID AT REST TO FLOW
Varies with depth

33
Q

What often drives fluid flow

A

Differences in pressure (gradients)

34
Q

Temperature

A

Measure of internal energy

35
Q

Ideal gas law

A

PV= nRT

36
Q

Density equals:

A 
ρ= m/V
ρ= n/V= P/RT
37
Q

Specific weight

A

Weight per unit volume

γ= ρg

38
Q

Archimedes’s Principle:

If an object is submerged, there is a…

A

Net force on the one because the pressures at the top and bottom of it are different

39
Q

Buoyant force

A

The upward force on the same volume of fluid that the object displaces
FB= F2-F1= ρgA(h2-h1)
FB= ρgV
FB= mg

40
Q

The net force on a submerged object is…

A

The difference between the buoyant force and gravitational force
ΣF= FB-Fg

41
Q

If an object’s density is less than that of water, there will be…

A

An upward ΣF on it

It will rise until it is partially out of the water

42
Q

For a floating object, the fraction that is submerged is given by….

A

The ratio of the object’s density to that of the given fluid

43
Q

Why do helium balloons rise?

A

Archimedes’s principle

44
Q

For fluids in motion, we will deal with…

A

Laminar flow (no turbulence)

45
Q

Mass flow rate

A

The mass that passes a given point per unit time
Flow rates at any two points must be equal, as long as no fluid is added or taken away
FR= V/t= Av

46
Q

Equation of continuity

A

Because flow rates at any two points must be equal, as long as no fluid is added or taken away
ρ1A1v1 = ρ2A2v2

47
Q

Bernoulli’s equation

A

Because fluid can also change its height
P + 1/2ρv^2 + ρgy= constant
Tells us that as the speed (v) increases, the pressure (P) decreases

48
Q

Drag

A

Is a function of pressure and friction
Fdrag= 1/2CDρAv^2
Acts in opposite direction to the motion of the object

49
Q

Drag coefficient

A

CD= CD,pressure - CD,friction

Depends on shape

50
Q

Lift

A

Acts at right angles to drag

Caused by pressure differential between top and bottom wing

EGR 1301 (16 decks)

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