2.2.2 Mechanics- Kinetics Flashcards
What is speed?
Constant forward movement without acceleration (constant velocity).
What is the equation for acceleration?
V²-U² divided by 2x distance
In what situation does acceleration remain constant?
When caused by earths gravitational attraction.
What is gravities standard value?
9.8m/s²
What is uniform circular motion?
Motion of an object in a circle at a constant speed, continually changing direction.
What is uniform circular motion also known as?
Centrifugal/Centripetal
What is centripetal force?
The force needed to keep an object moving in a circular motion and is facing in towards the centre.
What is the difference between centripetal and centrifugal?
Centripetal pulls the object in like gravity, centrifugal wants to push it away.
What is pendular motion?
The movement of a pendulum when it is given a small displacement and allowed to swing under gravity.
In pendular motion what is the angular amplitude?
Angular displacement from rest to maximum swing position.
In pendular motion what is the oscillation?
One complete swing
In pendular motion what is the length of the pendulum?
Distance from pivot to bob.
In pendular motion what is the frequency?
Number of cycles completed in unit time.
Does the mass of the bob make a difference to periodic time?
No
In pendular motion what is the periodic time?
Time taken to complete one oscillation.
What changes the periodic time of a pendulum?
The length of the pendulum.
What is damping?
Decrease of oscillations as a result of removing energy through resistance to motion.
What is free vibration?
When a mechanical system is set off with an initial input and then allowed to vibrate freely.
What is forced vibration?
When a continuous force is applied to a mechanical system.
What is a harmonic?
Periodic vibration. Sinusoidal with constant amplitude.
What are the two waves in a harmony?
The harmonic and the fundamental frquency?
What is resonance?
The tendency of system to oscillate at a max amplitude at a certain frequency.
What is the equation for wavelength of a harmonic?
2 divided by index of harmonic x length of the body
What is the equation for resonance frequency?
1 divided by 2π x square root of gravity divided by length.
What happens if a aircraft component vibrates at its resonant frequency?
The oscillations will become really large and the component could be destroyed.
What do machines do?
Let us do more work easily but not reduce the amount of work.
What is the velocity ratio?
The ratio of the distance moved by the point of application of the effort.
What does it mean if the velocity ratio is greater than one?
The distance moved by the point of effort is greater than the distance moved by the load.
What is the equation for mechanical advantage?
Resistance/Effort
What is actual mechanical advantage?
Tells us how much easier the work can be done.
What is the equation for mechanical advantage?
Output force/ Input force
What is ideal mechanical advantage and what is the equation?
Mechanical advantage if there were no resistance in the machine.
Input distance/output distance
What is a lever?
Rigid bar capable of turning around a fulcrum.
What are the parts of the lever?
Fulcrum, force and effort.
How do you calculate the effort required to lift a weight using a lever?
Work out the moments…Effort x length of arm = Resistance x length of arm
If a question asks what is the mechanical advantage what steps must you take?
Rearrange the opposing moments formula to find effort: F1 = F2 x S2 divided by S1. This will give you the effort which can then be used in MA= R/E.
What is a second class lever.
Fulcrum at one end rather than in the middle, i.e a wheelbarrow.
What is an inclined plane?
A surface inclined to a horizontal plane at any angle but 90 degrees.
What is a spur gear?
Teeth cut straight and used to connect two parallel shafts, they will turn in opposite directions.
If you want spur gears to turn in the same direction what must one of them have?
Internal teeth.
What is a bevel gear?
Teeth cut into a conical surface known as the pitch zone.
Where are bevel gears used?
Transmit forces perpendicular to one another.
What is worm gear?
Steering rack.
When is a worm gear used?
When a large reduction in speed is needed and for high toque multiplication.
What is the input gear in sun and planet gears?
The sun.
How does sun and planet gears work?
Planet gears are held together by a cage driven around the sun gear and engage at their outer edge in a fixed ring gear which does not rotate.
What is the output of a sun and planet gear?
The cage which is rotating slower than but in the same direction as the sun.
What is an example of a sun and planet gear?
Propeller reduction gear.
Where are sun and planet gears used?
Where space and weight is an issue but a large amount of speed reduction and torque is required.
What is efficiency?
Ratio of work which is transferred to a useful form compared to the total input work.
Why can’t any machine be 100% efficent?
Loses like heat, friction, deflection and wear and tear.
What is a third class lever?
The effort is applied at the fulcrum. i.e. landing gear.
How do you work out the mechanical advantage of gears?
Driven gear teeth divided by drive gear teeth.
