2.2 Mechanics - Kinetics (Lvl 2) Flashcards
What is motion?
A continuing change of position or the process in which a body undergoes displacement.
How could motion be described in an object?
When it is at different points in space at different times.
How would the motion be uniform?
When the distance the object moves remains the same for a given period of time.
What does a body change when its acceerates?
Speed or direction.
In linear motion, what changes when a body acclerates?
A change in speed.
Which type of acceleration remains constant?
Earth gravitational attraction.
What is the standard value for graviational accerlation?
9.8m/s^2.
What is uniform circular motion?
An object that is in motion in a circle at a constant speed, which is continually changing its direction.
What is the force required to keep an object moving in a curve path?
Centripetal force.
What is the formula for centripetal force?
centripetal force = mass x velocity^2/radius.
What is the meaning of centripetal accelration?
Because there is a constant change in direction, therefore a constant change in accerlation.
What is the meaing of centrifugal force?
The force that is equal to centripetal force, but in an opposite direction.
What always act at the same time on an object moving in a circular motion?
Centripetal and centrifugal force.
Which force keeps an object moving in a curved path directed towards the centre of rotation?
Centripetal force.
Which force keeps an object moving in a curved path directed way from the centre of rotaion?
Centrifugal force.
What does pendual motion describe?
The movement which the pendulum will undergo if it is given a small displacement from its vertial position and then allowed to swing freely under gravity.
What are the important terms associated with pendular motion? (6)
- Angular amplitude.
- Oscillation/vibration
- length of the pendulum
- periodic time
- cycle
- frequency.
What is angular ampltiude?
Angular displacement from rest to maxiumum swing position.
What is oscillation/vibration?
One complete swing to and from maximum position.
What is the length of pendulum?
Distance from the pivot point to the centre of gravity of the bob.
What is period time?
Time taken to complete one oscillation.
What is a cycle?
The motion completed in one period.
What is frequency?
Number of cycles completed in unit time.
What has been visible from experiments regarding a pendulum?
That provided the pendulum has a displacement of only a few degrees, that the periodic time remains constant even as the movement slows down.
What other variable makes no difference to period time of a pendulum?
The mass of the bob.
What variable changes the periodic time?
The length of the pendulum.
What can be said about the length of the pendulum?
The period of a pendulum increases with an increase in pendulum length or decrease in gravity.
What is damping?
Is a decrease of vibrations as a result of removing energy through resistance to motion.
Why is damping necessary in aircraft?
To control vibrations in order to prevent them from damaging aircraft components.
Why might vibrations be desirable?
Necessary for the function of the particular device.
How might vibrations be undesirable?
Imbalances from rotating parts.
What are the two types of vibration?
- Free vibration
2. forced vibration.
What is free vibration?
When a mechanical system is set off with an inital input and then allowed to vibrate freely.
What is forced vibration?
When a continuous force or motion is applied to a mechanical system.
In forced vibration, what is the frequency of he vibration dependant on?
The force or motion applied.
In forced vibration, what is the magnitude of the vibration strongly dependant on?
The behaviour of the mechanical system.
What is resonance?
The tendancy of a system to oscillat at a maximum amplitude at a certain frequency.
What form of vibration is useful in electrical circuits?
Resonance.
What is velocity ratio?
The ratio of the distance moved by the point of application of the effort to the distance moved by the load in a simple machine.
What is the formula for velocity ratio?
Velocity ratio = distance in/ distance out.
What is mechanical advantage?
The ratio of the forced produced by a machine to the force applied to it.
What is mechanical advantage used for?
Assessing the performance of the machine.
What is the formula for mechanical advantage?
Mechanical advantage = resistance/effort.
What is actual mechanical advantage?
The ratio of the output force and the input force.
What does actual mechanical advantage tell us?
How much easier the work can be done.
What is the formula for actual mechanical advantage?
actual mechanical advantage = output force/ input force.
What is ideal mechanical advantage?
The mechanical advantage that would exist if there were no friction in the machine.
What is the formula for ideal mechanical advantage?
ideal mechanical advantage = input distance / output distance.
What is the simplest machine?
The lever.
What are the three basic parts of a lever?
- the fulcrum
- force 1 or effort applied at a distance from the fulcrum.
- a load or resistance which acts at a distance from the fulcrum.
What is a first class lever?
Where a fulcrum is between the effort and load applied to a rod.
What is the formula for a first class lever?
f1 x s1 = f2 x s2
What is a second class lever?
The fulcrum is at one end of the lever and the effort is at applied to the opposite end, with the resistance in between the two.
What is the most common type of lever?
Third class lever.
What is a third class lever?
The fulcrum at one end, with the effort in between the load/resitance and the fulcrum.
What is an inclined plane?
A plane surface inclined to a horizontal plane at any angle other than a right angle.
How does an inclined plane achieve an advantage?
By allowing a large resistance to be moved by a small effort over a long distance.
How would you calculate the effort required for an inclined plane?
Using the same formula as first and second class levers.
F1 x s1 = F2 x s2.
How are pulleys similar to levers?
Because the location of the pulley determines whether it is a 1st, 2nd or 3rd class lever.
How would you determine the mechanical advantage of a pulley?
Count the number of ropes that move or support a moveable pulley.
What happens when mechanical advantage is gained?
The distance on which effort is applied increases.
Ie, MA of 2, for every 1m the resistance moves, effort must be applied to 2m of rope.
How is mechanical advantage gained through gears?
Variable number of teeth used on the drive or driven gear.
How do you calculate the mechanical advantage of gears?
MA = driven gear/ drive gear.
How do you calculate the force input when turning a gear?
= (gear ratio divided by each other) x force applied
What is torque proportional to?
Horsepower.
What is torque inversely proportional to?
Rotational speed (rpm).
What is the formula for horsepower?
Hp= torque x rpm/ 5252.
What does the constant 5252 represent?
Converting rpm to radians per second.
What is the difference between revolution ratio and gear ratio?
Revolution ratio is opposite to gear ratio.
Gear ratio = 2:1
Revolution ratio = 1:2.
What is a spur gear?
Teeth cut straight across their circumference and are used to connect two parallel shafts.
Which direction does a spur gear rotate if both gears have external teeth?
In opposite directions to each other.
Which direction does a spur gear turn if one of gears has internal teeth?
In the same direction as each other.
What is a bevel gear?
Gear having teeth cut into a conical surface known as the pitch zone.
When would a bevel gear be used?
When the drive and drive shafts are not parallel to each other.
What direction do bevel gears rotate and why?
In opposite directions to each other because they have external teeth.
At what angles can bevel gears be used?
Any angle below 180 degrees, but typically 90 degrees.
What is a worm gear?
A toothed wheel worked by a short revolving cylinder called the worm, resembling a screw thread
When would a worm gear be used?
When a large reduction in speed in needed and correspondingly high torque multiplication.
What is a sun and planet gear?
A drive gear (sun), drives the driven gear (planets) around a fixed outer ring.
Which direction is the output gear rotating in a sun and planet gear?
In same direction as the sun gear.
When is the sun and planet gear often used?
When space and weight are an issue and when a large amount of speed reduction and torque is needed.
What is efficiency?
The ratio of work which is transferred to a useful form compared to the total input work.
Why can’t a machine be 100% efficient?
Because of losses such as heat, friction, deflection as well as wear and tear.
