Flashcards in Engineering Final Deck (44)

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1

## What is mechanics?

### The study of the state of rest or motion of bodies that are subjected to forces.

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## What are the general areas of mechanics? Describe each, and list the subtypes.

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Rigid-body mechanics - Deal with the mechanical characteristic of bodies that do not deform under the influence of forces.

Deformable-body mechanics - Often referred to as mechanics of materials or strength of materials, Deals with solid bodies that deform under the influence of forces.

Fluid mechanics - Deals with the behavior of liquids and gases at rest and in motion. Technically deformable materials, however deformable-body mechanics deals exclusively with solids.

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## What is equilibrium?

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Equilibrium is a state in which a body is at rest with respect to its surroundings. When a body is in equilibrium, the forces that act on it are balanced, resulting in no motion. A state of equilibrium also exists when a body moves with a constant velocity, but this type of equilibrium is a dynamic equilibrium, not a static equilibrium.

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## What are the two types of rigid-body mechanics?

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Static deals with rigid bodies that are in equilibrium, that is, at rest with respect to its surroundings.

Dynamics deals with rigid bodies that are in motion with respect to its surroundings or other rigid bodies.

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## What are the two types of deformable body mechanics?

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Elasticity deals with the behavior of deformable solid material that return to their original size and shape after a force is removed.

Plasticity deals with the behavior of solid materials that experience a permanent deformation after a force is removed.

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## What are the two types of fluid mechanics?

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Fluid statics deal with fluids at rest.

Fluid dynamics deal with moving fluids.

7

## What is a scalar and what is a vector?

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A scalar is a quantity having magnitude, but no direction. Having magnitude only, a scalar may be positive or negative, but has no directional characteristics. Common scalar quantities are length, mass, temperature, energy, volume, and density.

A vector is a quantity having both magnitude and direction. A vector may be positive or negative and has a specified direction in space. Common vector quantities are displacement, force, velocity, acceleration, stress, and momentum.

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## What is the product of a scalar and a vector?

### The result is a vector, the resultant vectors magnitude may be changed by the scalar, however it's direction can not be, unless the scalar is negative in which case the vectors direction is reversed.

9

## How do you add two vectors, A and B?

### One of the best ways is to break the vectors into their base components. That is take the individual x and y coordinates of the vectors directions (Ax, Ay, Bx, By) and add them together ((Ax + Bx) + (Ay + By)).

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## How do you break a vector into it's base components? How do you form a vector from it's base components?

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If A is the magnitude and a is the angle of the direction that the vector lies on:

Ax = A cos(a)

Ay = A sin(a)

-ALTERNATIVELY-

Ay = Ax tan(a)

Form a vector from two base components:

A = sqrt(Ax^2 + Ay^2)

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## What is a unit vector?

### A dimensionless vector of unit length used to specify a given direction. This means multiplying a scalar and a unit vector will give you a vector with the magnitude of the scalar and the direction of the original vector.

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## How do unit vectors apply to finding a resultant vector?

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Because the base components Ax, Ay, are only scalars, we need to use unit vectors in order to add the direction back into the equation, resulting in a vector as a final answer. If i represents a unit vector completely on the x-axis, and j represents a unit vector completely on the y-axis this is what the resultant vector equation would look like:

A = Axi + Ayj

B = Bxi + Byj.

R=A+B=(Ax +Bx)i+(Ay +By)j

-ALTERNATIVELY-

Rx = Ax + Bx

Ry = Ay + By

R = Rxi + Ryj

Rx =R cos(u)

Ry =R sin(u)

Ry =Rx tan(u)

13

## What is a force?

### Force is defined as an influence that causes a body to deform or accelerate.

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## What are the types of force?

### Contact force, gravitational force, cable force, pressure force, or fluid dynamic force.

15

## What is a force system?

### A situation in which more than one force acts on a body.

16

## What are the types of electrical circuits?

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Power

-Power Generation: With a motor you insert electrical energy and it spins a shaft, creating mechanical energy. A generator works the opposite way, you spin the shaft, i.e. insert mechanical energy, and you get out electrical energy. One of the most common methods to do this is to attach fan blades to the shaft, and spin it using steam.

-Lighting/Heating

-Motors & Generators

-Signals

-Communication

-Computers

-Instruments & Controls

17

## What is current?

### If you have a wire, and take a cross section of that wire at any point, how much charge is passed through this cross section over a given period of time? (Current = charge / time)

18

## What is Ohm's law?

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Ohm’s Law: The potential difference across a conductor is directly proportional to the current.

V = RI

V = Voltage drop across the resistor

R = The resistance

I = Current going through the resistor

19

## How do you measure power?

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Power: P = VI

P = power, measured in Watts (W)

20

##
What are resistors in series?

What are resistors in parallel?

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In series: When you have two resistors (R1 and R2) right after another. One clue that a resistor is in series is that the two resistors have one common point. If two resistors are in series, you can replace them on paper with one resistor (denoted as Req); Req = R1+R2. Resistors in series have the same current.

In parallel When you have two resistors (R1 and R2) parallel to each other. One clue that resistors are in parallel, is that energy coming in has a fork where a decision must be made, some electrons will go one way, and other electrons will go the other way. If two resistors are in series, you can replace them on paper with one resistor (denoted as Req); 1/Req = 1/R1 + 1/R2.

Resistors in parallel have the same voltage.

21

## What is renewable energy, what are the types?

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Renewable Energy: Replenished at a rate more than it is being used i.e. solar power

Renewable energy and green energy are not necessarily the same, although there is a lot of overlap

Types of renewable energy: Solar, wind, hydro, geothermal, marine, biomass/biofuel, tidal

22

## What is density?

###
Mass per unit volume

𝜌 = m / V

SI Units = kg/m3

USCS Units = slug/feet3

23

## What is specific weight?

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Weight per unit volume

Ɣ = W/V

SI Units = N/m3

USCS Units = lb/ft3

24

## What is the relationship between weight and mass?

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W = mg

G = force of gravity

Ɣ = W/V

Ɣ = mg/V

Ɣ = 𝜌g

25

## What is specific gravity?

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Density of water at 4°C = 1000kg/m3

Specific gravity is the ratio of density to density of water at 4°C

sg = 𝜌 / (𝜌h2o@4°C)

This value is dimensionless

26

## What does incompressible mean?

###
An object that, if you place equal pressure on it from all sides, does not compress to a smaller state

27

## What is thermodynamics?

### The science of energy transformation and utilization.

28

## What is the first law of thermodynamics?

### States that energy can be converted from one form to another, but the total energy remains constant. A popular statement of the first law of thermodynamics is that energy cannot be created or destroyed.

29

## What is the second law of thermodynamics?

### States that energy conversions occur in the direction of decreasing quality of energy. For example, a hot beverage on a table eventually cools by itself to the temperature of the surroundings, thereby degrading the energy of the high temperature beverage into a less useful form.

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