Mechanical Systems 1-2 Flashcards
what were early machines dependant on for energy?
people or animals
what is a simple machine?
a tool or device made up of one basic machine
what are the 6 simples machines?
● Lever
● Inclined plane
● Wedge
● Screw
● Pulley
● Wheel and axle
what are levers and what do they do?
● Rigid bars that can rotate around a fixed point called a pivot or fulcrum.
● Reduce the force or effort needed to carry out a task, such as hitting a
baseball, opening a bottle, pulling a nail and cutting paper.
● You can move a larger load, but you must move a greater distance.
what are the 3 types of levers?
There are 3 types of levers:
● First class lever - the fulcrum (F) is in the middle (between the load & the effort)
● Second class lever - the load (L) is in the middle (between the
fulcrum & the effort)
● Third class lever - the effort (E) is in the middle (between the
fulcrum & the load)
Remember: F, L, E = 1, 2 , 3
give an example of a first, second, and third class lever
- see saw
- wheel barrow
- snow shovel
what is an inclined plane?
● Alternatively, a ramp
● Makes it possible to lift heavy objects using a smaller force.
● You have to exert the force over a longer distance (compared to
lifting the object straight up).
● An inclined plane is only useful for small inclines.
what is a wedge?
● Is forced into an object.
● By pressing on the wide end of a wedge, you can exert a
greater force on the narrow end so it splits an object.
● A wedge can only be used in one direction.
what is a screw?
● A cylinder with a groove cut in a spiral on the outside.
● Using a screw increases the force needed to penetrate materials.
● A screw converts rotational (turning) motion to linear (straight line)
motion.
you use less effort, it creates more force
what is a pulley?
● Consists of wire, rope (or cable) moving on a grooved wheel.
● Pulleys can be made up of 1 or many wheels and can be
fixed in place or moveable.
● Pulleys help you lift larger loads than you could lift on your
own.
what is a wheel and axle?
● A combination of 2 wheels of different diameters that turn
together.
● A longer motion on the wheel produces a shorter but more
powerful motion at the axle.
● Can increase force, like a steering wheel and steering column. It can
also be used to increase speed, like wheels on a bike.
what are the 4 effects of simple machines?
- Changing the direction of force (e.g. pulley on
a flagpole) - Multiplying force (e.g. screwdriver)
- Increasing or decreasing speed (e.g. scissors)
- Transferring force (e.g. staple remover)
what are complex machines?
Devices that are made of several
simple machines
what is a system?
group of parts that work
together to perform a function
what is a subsystem?
● Within a complex machine there are groups of
parts that perform specific functions
● Subsystem has only one function
● In a bicycle, the steering system or braking
system
● Subsystems work together to complete the
task of the complex machine
what are linkages?
Transfers energy from an energy
source to an object
how do chains and belts work?
● Form a direct link between two separate wheels.
● One wheel turns, the other will turn in the same direction
● If a wheel is larger it will turn slower, but with a greater force
● Chains have less chance of slipping than belts
● Belts are more flexible
how do transmissions work?
● Contains a number of different gears
● Able to move much larger loads
● Can use a large force to move objects slowly
● Can use a small force to move objects quickly
what are gears?
● Wheels with teeth that interlink
● One wheel transfers energy to the other, while rotating
● Gears can be used to change speed and direction of
motion
how do gears work?
● Control the transfer of energy in a system
● Work in gears trains of two or
more gears
what’s the difference between the driving and driven gears?
● Driving gear: Has force applied from outside the gear train
● Driven gear : has a force applied to it by the
driving gear
this is very top and bottom gay core but the driven gear is not always underneath the driving gear, it can be the other way around
how do gears affect speed?
● Different sizes of gears linked together in a chain with
change the speed of the system
● It will also change the amount of power the system has
what is it called when the driving gear is bigger than the driven gear?
● Known as multiplying gears
● Turning speed in the system increases
● When you rotate the large gear once the small one
rotates several times
what is it called when the driven gear is bigger than the driving gear?
● Known as reducing gears
● Turning speed in the system decrease
● When you rotate the smaller gear once the large one
rotates only a fraction
how does transmission work in a car?
Driver can select a low gear to get started, change to a higher gear once they are going quickly on the highway
what is low gear in a car?
● Transmission connects a small wheel to a large wheel
● Wheels rotate more slowly than the engine. Means
more power, less speed
what is high gear in a car?
● Transmission connects a large
wheel to a smaller wheel
● Wheels rotate more quickly than engine. Means less power, higher speed
what happens when you shift gears in a car?
● Gear wheels do not mesh directly
with one another
● Joined by a chain, which provides
a linkage between gears
● When shifting you move the
chain from one gear wheel to
another
● You can control how fast you are
going when you pedal
what is mechanical advantage?
The amount by which a machine can multiply a force
what is the difference between output and input energy?
● Input force: Force applied to the machine
● Output force: Force the machine applies to the object
how do you calculate mechanical advantage?
Mechanical Advantage (MA) = Output Force
Input Force
● Also known as the force ratio
● Has no units
what is speed ratio?
● Speed measures the distance an object
travels in a given amount of time
● Speed ratio: measure pf how the speed
of an object is affected by the machine
how do you calculate speed ratio?
Speed Ratio (SR) = Input Distance
Output Distance
● Again, no units
explain the less force —> greater force
● Trade off for increased force, moving a further distance
○ Seen in the examples of pulleys. Pull the rope 4m to move the
load 1m.
● Can also be seen in ramps
○ Longer the ramp, less force to change elevation but you have
to push the object a longer distance
what does it mean when the mechanical advantage is less than one?
● Means the output force is smaller than the input
force
● Useful for tasks where a large output force is not
needed
what creates the difference between speed ratio and mechanical advantage?
friction
what is the effect of friction?
● Theoretical and practical values may be different due to
friction
● Friction: a force that opposes motion
● A rough surface creates more friction than a smooth one
● Extra force is needed to overcome friction
● Friction causes heat, an additional problem in
mechanical systems
○ Requires lubricants or fans
what does friction change?
● Mechanical advantage changes due to friction
● Speed ratio DOES NOT change due to friction
○ You still have to move the object the same distance
● Speed ratio represents the ideal mechanical advantage
what is efficiency?
● How well a device uses its energy
● Any machine operating loses some of its energy,
usually to friction
● More energy lost, the less efficient the machine is
○ A machine that is 40% efficient is less efficient than a machine
that is 70% efficient
how do you calculate efficiency?
Efficiency = Mechanical Advantage x 100
Speed Ratio
● Efficiency is recorded as a percent
how do complex machines differ efficiency wise?
● With many different subsystems they all have their
own inefficiencies
● Complex machines tend to be very inefficient
● A car engine is only around 15% efficient
what is work?
● When a force acts on an object to make an object move
● You can apply a ton of force to a wall, as long as is
doesn’t move you’re not doing work
how do you calculate work?
W = F x d
Work = Force x distance
● Force measured in Newtons, distance in
metres
● Work measured in Joules with is equivalent
to a Newton metre
how are energy and work related?
● Energy and work are closely related.
● Can’t do work without energy
● When you ride a bike you use your energy to
apply force to the pedals.
● The force is transferred through the bike and
you move
● Work is being done!
how are work and friction related?
● Work input and output are not always the same
● Again, it’s friction
● We can also calculate efficiency using work input and
output
● Efficiency = Work output x 100
Work input
what are hydraulics?
● Uses liquid under pressure to move loads
● Increases mechanical advantage
● Has revolutionized industries like construction
what is pressure?
amount of force applied to a given
area
what is pascals law and what does it make possible?
Pressure applied to an
enclosed fluid will be
transmitted equally in all
directions
● Makes hydraulic (liquids) and
pneumatic (gases) systems
possible
what is a piston?
● Piston: disc that fits tightly in a cylinder,
● Disc moves inside cylinder
● The piston will either push out or draw fluid into the
cylinder
what are the hydraulic devices output and input pistons?
● Combination of two pistons attached by a flexible pipe or cylinder
● Input piston: first piston, applies the force
● Output piston: Pressure is transferred to this piston through the fluid
● Pressure on output piston is equal to pressure created by input piston
what is the mechanical advantage in hydraulics?
● Comes from the fluid pressure in the system
● Force applied to the input piston
● Pressure transfers throughout the fluid
● Pressure pushes on the output piston
how are pressure and mechanical advantage related?
● Pascals Law creates the great mechanical advantage in hydraulic
systems
● You’re able to apply a small force on a small piston and get a large
force on the large piston
how do you calculate pressure/pressure ratios?
● We must recall the pressure formula
● P = F/A
● Pressure must be equal on both pistons
● Pressure small piston = Pressure Large piston
Therefore…
Force Small Piston = Force Large Piston
Area Small Piston Area Large Piston
explain the larger force –> greater distance
To increase force on the output piston, the
input piston has to move a greater distance
