2.2.1 Mechanics- Statics Flashcards
What is the definition of distance?
A length between two points.
What is the definition of speed?
The rate of change of distance in a given time regardless of direction.
What is the definition of velocity?
The rate of change of distance in a given time in a specified direction.
What is the definition of acceleration?
A rate of change of velocity.
What is the definition of weight?
The weight of a body is the gravitational force with which the body experiences.
What is the formula of force?
Mass x acceleration
What is the definition of a newton?
The force that gives 1kg an acceleration of 1 m/s.
What is the definition of kilogram force?
Magnitude of force exerted on 1 kilo of mass x gravity.
What is the formula of weight (kgf)?
mass x local value of gravity divided by 9.0865
Where is the weight of a body concentrated at?
Centre of gravity.
What happens to forms that are hollow with their centre of gravity?
It may occur in space and provides a convenient point from which to make calculations.
If a force goes through the centre of gravity what happens?
It remains balanced.
What happens if the force acts away from the centre of gravity i.e. the wing tip?
It produces a turning effect.
What is the formula for moment (Nm)?
Force (n) x Distance (m)
What is a clockwise moment?
Movement in a clockwise direction.
What is the moment if the distance is 4m and the force is 5Nm?
20Nm.
What is the equilibrium of translation?
The forces in one direction must equal the forces in the other.
What are quantities thought of as being?
Scalar or Vector.
What is a scalar quantity?
Contains magnitude only.
What are examples of scalar quantities?
Mass, time, temperature, lenghth etc.
What is important about the presentation of scalar quantities?
They are only represented graphically.
What is a vector quantity?
They posses magnitude and direction and if either changes then the vector changes.
What are examples of vector quantities?
Force, velocity and any quantity formed from these.
How is a vector quantity represented?
A line drawn to some scale, representing magnitude at an angle to a datum which indicates the the direction, an arrow showing the way the quantity is applied.
What do you need to know to represent a force in a vector?
The point of application
Its magnitude or size
Its direction
Its sense of direction
What is a co-planar force?
Acting in the same plane.
What is a concurrent force?
Acting at the same moment in time.
What is used to determine the actual force and direction when there are two forces acting on a body?
A vector addition, it does a vector the first force and adds it to the vector of the second force.
What is the resultant force?
The single force which could replace the original forces and yet have the same effect.
How do you read a vector?
Draw a line between the two forces to make a triangle and measure it, then using the scale convert it from cm to n. And you present the answer with the angle, e.g. 5n at 37 degrees.
What is the name of a force that is equal and opposite?
Equilibrant.
If a body is at equilibrium under three resultant forces where must they pass through?
A common point.
What is the triangle of forces?
Forces in equilibrium on a body drawn in a closed triangle all following each other. The forces must be concurrent.
What is it called when the reverse of a single resultant force is replaced with two forces?
Resolution.
What are the two forces in a resolution called?
Component forces.
What is stress?
Internal force that resists deformation of a body.
How is stress denoted?
Greek symbol sigma σ
What are the units for stress?
Nm¯²
What is the formula for stress?
Force applied (n) divided by cross sectional area (m²)
What are the 5 different types of stress?
Tension- stretch
Compression- squeeze
Bending-
Torsion- Twist
Shear- layers going opposite ways
What is torsion a combination of?
Tension and compression.
What are the two forces involved in bending?
Tension and compression.
When stress is applied to a material what is the deformation called?
Strain.
What is the formula for strain?
Change of length divided by the original length.
Why does strain not have units?
It is a ratio of two scalar quantities.
What is it called when the property of a material is to return to its normal shape after being under stress?
Elasticity.
What stress does youngs modulus refer too?
Elasticity
What is youngs modulus?
Stress over Strain
What is one of the most elastic materials?
Glass
What is the elastic limit?
The point of which the material can no longer return to its original shape.
What is hookes law?
The amount of stress deformation in a material is proportional to the stress as long as the elastic limit is not exceeded.
At the elastic limit, what is the point of permanent deformation known as?
The Yield Point.
What happens after the yield point if a force is still being applied?
Ultimate strength is reached and at this point the material will rupture or break.
What is the definition of force?
Interaction which tries to change the body state of rest or motion.
What is the metric system of foce?
Newton.
What is the imperial system of force?
Pound.
What is the metric and imperial systems for moment?
M= NM
I= lb-in
What is an opposing moment?
Total moments that act against each other are applied at points separated by a distance.
What is the fixed axis called?
Fulcrum
What is the principle of moments and what would it result in?
Opposing moments to have equal magnitudes, this would result in an object being balanced.
What is a couple?
A pair of forces that are equal in magnitude and opposite in direction. This produces a torque on the object.
What is the resultant?
The effect that results from two or more vectors of the same type of quantity acting on an object.
How do you work out the resultant of two vectors acting in the same direction?
Add them together.
What happens to the resultant of the vectors if they aren’t on 0 or 180 degrees.
They can’t be calculated.
How does triangle method work for working out the resultant of two vectors at 90 degrees to one another?
Draw the two vectors, complete the triangle. The length of the hypotenuse is the resultant and the angle shows the direction of travel.
How does Pythagoras work for working out the resultant of two vectors at 90 degrees to one another?
Pythagoras= a²+b²=c²
What is plasicity?
Opposite to elasticity, when a material changes shape permanently when subject to stress.
What is hardness?
Resistance to indentation.
What is toughness?
Tendency to resit breakage.
What is malleability?
To undergo compressive stress without damage.
What is ductility?
Tendency to undergo tensile stress without breakage.
What is vapour?
A gas that can be liquified by an increase in pressure without decreasing temperature.
What is volatile liquid?
A liquid that readily evaporates at room temperature.
What is the flash point?
The temperature at which a liquid will catch fire when exposed to a naked flame.
What does inert mean?
An inert substance will not chemically combine with another. All inert substances are gases.
In the metric system what is pressure denoted by?
Pa or Nm²
In the imperial system what is pressure denoted by?
Psi
What is the formula for pressure?
Force divided by area
What is atmospheric pressure?
The force exerted by the weight of the atmosphere.
What is the atmospheric pressure at sea level?
14.7 psi
What is the most common type of barometer?
Mercury
What is gauge pressure?
The amount of pressure by which the measured pressure in a fluid exceeds the atmosphere.
What is absolute pressure measured too?
Relative to the absolute zero pressure, meaning it occurs in a vaccum.
What is the formula for absolute pressure?
Gauge pressure + Atmospheric pressure
What does Archimedes principle state and what is the force known as?
A body in liquid will be subject to an upward force equal to the weight of the liquid it displaces. It is known as the buoyant force.
What happens if the buoyant force is more than the object weighs?
The object will float.
When does neutral buoyancy occur?
When the weight of the object is equal to the fluid it displaces.
What determines how high or low an object floats?
The ratio between the density of the object and the density of the fluid.
What is a Torricellian vacuum?
The weight of the mercury in a barometer in the reservoir creates a vacuum at the top of the tube which is nearly absolute zero.
What is the principle of moments?
When the two opposing moments are equal and the body can be balanced on its fulcrum.
What is a couple?
A pair of forces equal in magnitude but opposite in direction. They produce a torque on the object, such as a tap wrench.
What is the flashpoint of aviation fuel?
38 degrees Celsius.
