Aeroscience

Question 1

State the International System (SI) units for:

a) Length
b) Mass
c) Time
d) Temperature

Answer 1

a) Meters (m)
b) Gram (g)
c) Second (s)
d) Kelvin (K) / Degrees Celsius (°C)

Question 2

State the derivation of the SI units for:

a) Force
b) Pressure
c) Power

Answer 2

a) Newton (N)
b) Pascal (pa or hpa)
c) Watt

Question 3

State the units of measurement for:

a) Altitude
b) Navigational distance
c) Speed
d) Horsepower

Answer 3

a) Feet (ft) - 1ft = 0.3048m
b) Nautical miles (nm) - 1nm = 1,852m
c) Knots (kt) - 1kt = 0.514m/s or 1.85km/hr
d) Watts (W) - 1 horsepower = 746W (or roughly 3/4kW)

Question 4

Describe the trig functions for the sine, cosine and tangent of an angle

Answer 4

There are six functions that are the core of trigonometry. There are three primary ones that you need to understand completely:

Sine  (sin)
Cosine  (cos)
Tangent  (tan)

SOH - CAH - TOA

(Some Old Hags - Can’t Always Hide - There Old Age)

Sine
Cosine
Tangent

For example, the cosine of x is the side adjacent to x (labeled a), over the hypotenuse (labeled h):

If a = 12cm, and h = 24cm, then cos x = 0.5 (12 over 24).

Question 5

Describe the moment of a force, and the moment of a couple.

Answer 5

A moment is a turning force about a pivot or turning point. Other terms used for a turning force are torque and leverage. The strength of a moment is given by the product of the force and the perpendicular distance (called the arm) between its line of action and the pivot point. In the SI system, the moment of a force is measured in newton-metres (N-m).

A couple consists of two equal but opposite parallel forces. When the forces of a couple act around a point mid-way between the two, a turning force, usually referred to as torque, will be produced. The torque produced is the product of one of the forces and the perpendicular distance between the two. Again, in the SI system, torque is measured in N-m.

Question 6

Differentiate between scalar and vector quantities , and explain and/or apply vector addition and subtraction.

Answer 6

Scalar Quantity - a quantity which has only magnitude (or size). When we refer to a scalar quantity we are only concerned with the amount of the quantity (i.e. Temperature).

Vector Quantity - a quantity which has both magnitude and direction. When we refer to vector quantities, a direction must be specified, otherwise the quantity becomes scalar in nature. An example of a vector quantity is wind speed. It has both speed and direction and in aviation it is referred to as the wind velocity (W/V) vector.

Addition:

A + B = added Resultant

Subtraction:

A - B = subtracted Resultant

Question 7

Differentiate between centripetal force and centrifugal reaction.

Answer 7

Centripetal force acts toward the center of the turn and can be measured using the formula:

CPF = m x v² or CPF = W x v²
r gr

W = weight, m = mass, v = velocity vector, g = gravitational force, r = radius of curvature caused by the force.

Centrifugal force is equal and opposite to the centripetal force that acts on the object and can be measured using the formula:

CFF = m x v² or CFF = W x v²
r gr

Question 8

State Newtons First Law of Motion.

Answer 8

“Every object continues in a state of rest or of uniform motion in a straight line, unless acted upon by an external force”

Question 9

Differentiate between Mass and Inertia.

Answer 9

Mass - the amount of substance contained within an object, usually of indefinite shape and often of considerable size (measured in kg).

Inertia - the tendency of an object to continue moving at a certain velocity (or to remain at rest with zero velocity).

Question 10

Explain what is meant by the term Force?

Answer 10

A force can be described in various ways as a push or a pull, an attraction or repulsion, an influence, or a pressure on an object.

Question 11

State Newtons Second Law of Motion.

Answer 11

“The external force acting upon a body is proportional to the product of its mass and the acceleration produced by the force”.

Question 12

State the formula for Newtons Second Law of Motion.

Answer 12

Force = mass x acceleration

Force is measured in newtons (N), mass in kilograms (kg) and acceleration in metres per second per second (m/s2).

Question 13

Explain what is meant by the term Weight?

Answer 13

Weight is not the same as mass, it is the force that is produced when an object (or mass) is acted upon by gravitational attraction.

Weight = mass x gravity

In the SI system, an object’s weight on or near the earth’s surface will be:

Weight (in N) = mass (in kg) x 9.81 (m/s²)

Question 14

Explain what is meant by the term Momentum?

Answer 14

Momentum is the product of the mass and velocity of an object.

For example, a heavy truck moving rapidly has a large momentum - it takes a large or prolonged force to get the truck up to this speed, and it takes a large or prolonged force to bring it to a stop afterwards. If the truck were lighter, or moving more slowly, then it would have less momentum.

Momentum = mass x velocity

Question 15

State Newtons Third Law of Motion.

Answer 15

“Every action has an equal and opposite reaction”

Question 16

State the value of the acceleration caused by the earth’s gravity.

Answer 16

Acceleration due to gravity (g) applies to all masses on or near the earth’s surface.

It is a constant at 9.81 m/s2

Question 17

Explain the meanings of work, power and energy.

Answer 17

Work is done when a force moves an object through a distance.

Work = force x distance

Work is measured in Nm or joules (J).

1Nm moved through 1m = 1J

Power is the rate at which work is done.

Power = work done = force x distance
time taken time

Units are watts (W).

1W = 1Joule/second

Energy is the capacity to do work.

Measured in Joules (J).

Energy comes in many forms; chemical, mechanical, electrical, etc.

Question 18

Describe kinetic energy and potential energy.

Answer 18

Kinetic (or dynamic) energy is the energy due to motion. Every moving mass has kinetic energy and therefore the capacity to do work. The amount a mass has depends on its mass and its velocity.

Kinetic energy = ½ mass x velocity squared

Potential energy is the energy of position, e.g. something high like an aircraft can convert potential energy into kinetic energy to maintain speed in a gliding descent.

The unit for energy in the International System (SI) is the joule, which has the symbol J.

Question 19

Define speed, velocity and acceleration.

Answer 19

Speed

The distance travelled in a unit time, i.e. metres/second, kilometres/hour or of importance in aviation – in nautical miles/hour (or knots). In the way in which we use the term, speed is a scaler quantity.

speed = distance travelled
time taken

Velocity

The vector equivalent of speed. It is distance travelled in a given direction in unit time. The term velocity is used (rather than speed) when the direction of travel is important.

velocity = distance travelled in a given direction
time taken

Acceleration

If speed is increased, the acceleration is said to be positive. If speed is decreased, it is negative and usually referred to as deceleration.

Acceleration also occurs when there is a change in direction but not in speed. The direction of the acceleration is towards the centre of the curved path which exists at any given moment.

In summary, acceleration occurs whenever:

There is a change in speed, or
There is a change in direction, or
There is a change in both speed and direction.

A more concise way of phrasing the foregoing is to state that:

Acceleration occurs whenever there is a change in velocity.

Question 20

Explain the meaning of centre of gravity.

Answer 20

The weight of an object can be taken to act through its centre of mass - more often called its centre of gravity. If an object is suspended from its centre of gravity (or a point directly above it), it will balance and not rotate. If the suspension point (or some other pivot point) is displaced horizontally from the centre of gravity, a moment will exist and the object will not be balanced.