One
of the reasons insects don't hurt themselves when they fall is because
they have a low terminal velocity and are travelling relatively slowly
when they reach the ground.
Did you know that a child can probably produce more torque using their arm, than a lawn mower engine can generate to turn the blade? Surprisingly, the figure for the torque of a 5 hp engine used on a mower is 7 to 10 foot-pounds (ft·lbf) in the imperial system or 11.5 to 13.6 newton-meters (Nm). Applied torque is simply force multiplied by distance, so 1 pound-force applied over a distance of 1 foot from a pivot is 1 foot-pound. In the metric system, the unit of torque is the newton-metre (Nm). A torque of 1 Nm is equivalent to one newton—the SI unit of force—applied over a distance of one metre. The speed of a lawn mower blade is more important than torque, and blades are driven directly by the crankshaft without reduction or overdrive gearing. Blades typically spin at the engine speed of around 3000 RPM, giving a blade tip speed of around 200 mph, or 90 metres per second.
So while a child may be able to exert more torque with their arm than a mower engine can exert on a blade, they wouldn't be able to match its power. Another piece of the jigsaw is that the quoted figure of 11 to 13 Nm is for the drive torque from the engine. Since a blade is spinning at around 3000 RPM, it has a lot of inertia. The technical term for this when a rotating body such as a flywheel or blade is involved is moment of inertia. When a blade slows down as it impacts grass, the change in angular momentum creates a force, just like the way a car or any linearly-moving object creates a force as it slows down due to friction, or when it hits something (think of the huge force produced by a hammer, typically many tonnes, when it hits a nail). So the force produced by a blade as it impacts and shears grass is much greater than the force that the engine itself could have generated.
Note: You may be wondering why "newton" in "newton-metres" above isn't capitalised. The unit is named after the English scientist Isaac Newton. It's not a typo. In the International System of Units (SI), or Système international d'unités, units named after a person are not capitalised. However, the symbol is, N in this case, Units are normally lower case, as are prefixes. However, prefixes over one million are capitalised—so kilometres is km, but gigahertz is GHz.
In theory, according to Newton's first law, a body remains at rest, or in
motion at a constant speed in a straight line, unless it is acted upon
by a force. So if you kicked a ball in space and there were no planets
or stars to influence the ball, it would go on forever. That's how
deep-space probes work: during launch, engines fire to create thrust and
increase velocity typically up to 10 km/s or more. When the engine cuts out, a
probe will coast indefinitely, following a curved path due to the gravitational pull of planets and the Sun. Without gravity, the trajectory would be a straight line.
We
all know that when an object is released from a certain height, it
starts to fall. This, of course, is due to gravity, or more specifically
the gravitational force of attraction between the object and the Earth.
The force of gravity causes the object to accelerate and increase in
velocity as it falls downwards towards the Earth. In actuality, both the
Earth and the object are mutually attracted to each other, and the
Earth moves upwards at the same time. However, since it's so massive in
comparison to a small object and the force is so small, its movement is
minuscule.
A lever is a simple
device that works by changing the input force needed to do work and move
something. Some levers do this by magnifying the force applied to them.
In this tutorial, we'll explore how levers are used in our everyday
lives and then learn the simple physics of how they work.
Physics is an area of science which deals with how matter and waves behave in the universe. A branch of physics called mechanics deals with forces, matter, energy, work done and motion. A further sub-branch known as kinematics deals with motion and ballistics is specifically concerned with the motion of projectiles launched into the air, water or space.
When a force acts down on the apex of the truss, the forces in the tie can be greater than the load acting down on the apex. And if the slope of the truss becomes very shallow, the tension force in the tie can become huge and tend to infinity as the angle of the slope tends to zero.
Mechanics is a branch of physics which deals with forces, mass, and motion. In this second part of a two part tutorial, you'll learn the absolute basics! In the first tutorial, Examples of Forces in Everyday Life and How They Affect Things, we learned what force is and explored the various types of forces in the world around us.
What's Covered in This Guide?
Newton's three laws of motion and how an object behaves when a force is applied
In
the 17th century, the mathematician and scientist Isaac Newton came up
with three laws of classical mechanics concerning motion of bodies in
the Universe. These laws describe the relationship between the motion of
an object and the forces acting on it. In physics, objects have a
property called mass, measured in kg in the SI system (This stands for Système International d'Unités, the standard system of units used in science and engineering)
1. Newton's First Law of Motion: Rest or Uniform Motion
A body remains at rest, or in motion at a constant speed in a straight line, unless it is acted upon by a force
Basically,
this means that if for instance a ball is lying on the ground, it will
stay there. If you kick it into the air, it will keep moving. If there
was no gravity, it would go on for ever. However, the external force, in
this case, is gravity which causes the ball to follow a curve, reach a
max altitude and fall back to the ground. Friction from air also slows
it down.
Another example is when you put your foot down on the
accelerator and your car increases in speed. When you take your foot off
the accelerator, the car slows down, The reason for this is that
friction at the wheels and friction from the air surrounding the vehicle
(known as drag) causes it to slow down. If these forces were magically
removed, the car would stay moving forever. There are three scenarios for the first law: Two for when a body is at rest and one for when it's in motion.
Body at Rest
There are two scenarios for a body at rest:
Scenario 1: No forces acting on the body
In
the example of a body floating in deep space, far from any planets or
stars, where it isn't influenced by gravity, it will stay in this
position at rest forever. In reality of course, it will always be
influenced by gravity, even at huge distances, although the effect may
be tiny. In the diagram below, the body is given the symbol m,
representing its mass. The body doesn't have to be in space of course,
but this is an extreme example of a body so remote, that there are
extremely small forces acting on it.
In
reality, there will always be forces acting on a body. If forces cancel
out, there's no net force acting and again it stays at rest. An example
is an object with mass m suspended from a rope. The force of gravity
pulls down on the object. However the rope also pulls back up with a
tension force. These forces cancel each other out and there's no net
force.
This is
the 3rd scenario of Newton's 1st law. When a body is acted on by a net
force, it accelerates and reaches a certain velocity. When that force is
removed, it continues to travel at that velocity, unless another force
acts on it. Again, the reason why we don't see this ideal behaviour
happening in the real world and objects continuing to move without
slowing down is because external forces act, usually friction and drag
due to air. We see approximations though, so a spinning top will spin
for a long time if it has a pointed foot that has little friction wit
the surface on which it rests. Similarly a bowling ball or marble will
roll a long way on a hard level surface without stopping.
2. Newton's Second Law of Motion: Force and Acceleration
The acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass
This
means that if you have an object and you push it, the acceleration is
greater for a greater force. So for example a 400 horse power engine in a
sports car is going to create loads of thrust at the axle and
accelerate the car to top speed much more rapidly than a regular engine
would be capable of achieving with the same weight of car.
In the
SI system of units, force is measured in Newtons (N), mass is measured
in kilograms (kg) and acceleration is measured in metres per second per
second (also known as metres per second squared) (m/s2)
So:
If F is the force in Newtons (N)
m is the mass in kilos (kg)
and a is the acceleration (m/s2)
Then we can write an equation for Newton's 2nd law:
F = ma
This
tells us that the mass of a body multiplied by its acceleration equals
the force applied to that body that gave it the acceleration a.
We can also rearrange the equation so
a = F / m
What does this equation tell us?
Acceleration is proportional to the applied force
So the acceleration is directly proportional to the applied force. Double the force F and a doubles. Triple the force F and a is tripled and so on.
Acceleration is inversely proportional to the mass
For larger masses, acceleration is smaller for the same force. So for example, In the equation above if we double m, a is halved.
Imagine
in the example above that the sports car engine was placed into a heavy
train locomotive and could drive the wheels. Because the mass of the
locomotive is so large, the force creates much lower acceleration and
the locomotive takes much longer to reach top speed (In the equation, F is the same, but m is below the line, so a is smaller).
3. Newton's Third Law of Motion: Action and Reaction
For every action, there is an equal and opposite reaction.
This means that when a force is exerted on an object, the object pushes back.
Some examples:
When you push on a spring, the spring exerts a force back on your hand. If you push against a wall, the wall pushes back.
When you stand on the ground, the ground supports you and pushes
back up. If you try to stand on water, the water cannot exert enough
force and you sink.
Foundations of buildings must be able to support the weight of the
construction. Columns, arches, trusses and suspension cables of bridges
must exert enough reactive compressive or tensile force to support the
weight of the bridge and what it carries.
When you try to slide a heavy piece of furniture along the floor,
friction opposes your effort and makes it difficult to slide the object
As
we saw above, friction is an example of a force. When you attempt to
slide a piece of furniture along a floor, friction opposes your effort
and makes things more difficult. Friction is an example of a reactive
force, and doesn't exist until you push the object (which is the active
force). Initially, the reaction balances the applied force i.e. your
effort pushing the furniture, and there is no movement. Eventually, as
you push harder, the friction force reaches a maximum, known as the limiting force of friction.
Once this value is exceeded by the applied force, the furniture will
start to slide and accelerate. The friction force is still pushing back
and this is what makes it so difficult to continue to slide the object.
This is why wheels, bearings, and lubrication come in useful as they
reduce friction between surfaces, and replace it by friction at an axle
and leverage to overcome this friction. Friction is still necessary to
stop a wheel sliding, but it doesn't oppose motion. Friction is
detrimental as it can cause overheating and wear in machines resulting
in premature wear. So engine oil is important in vehicles and other
machines, and moving parts need to be lubricated.
Dry static friction, also known as stiction (see above diagram)
If F is the applied force on a body
The mass of the body is m
Weight of the body is W = mg
μs is the coefficient of friction (low μ means the surfaces are slippery)
and Rn
is the normal reaction. (the reaction force acting upwards at right
angles to the surface due to the weight of the object acting downwards)
If the surface is horizontal, then
Reaction Rn = Weight W
Then
limiting friction force is Ff = μsRn = μsW = μsmg
Remember
this is the limiting force of friction just before sliding takes place.
Before that, the friction force equals the applied force F trying to
slide the surfaces along each other, and can be anything from 0 up to μRn.
So
the limiting friction is proportional to the weight of an object. This
is intuitive since it is harder to get a heavy object sliding on a
specific surface than a light object. The coefficient of friction μ
depends on the surface. "Slippery" materials such as wet ice and Teflon
have a low μ. Rough concrete and rubber have a high μ. Notice also that
the limiting friction force is independent of the area of contact
between surfaces (not always true in practice)
Kinetic Friction
Once
an object starts to move, the opposing friction force becomes less than
the applied force. The friction coefficient in this case is μk.
What Are Newton's Equations of Motion? (Kinematics Equations)
There
are three basic equations which can be used to work out the distance
travelled, time taken and final velocity of an accelerated object.
First let's pick some variable names:
u is the initial velocity
v is the final velocity
s is the distance covered
t is the time taken
and a is the acceleration produced by force F
As long as the force is applied and there are no other forces, the velocity u increases uniformly (linearly) to v after time t.
So for uniform acceleration we have three equations:
v = u + at
s = ut + 1/2 at2
v2 = u2 + 2as
Examples:
(1)
A force of 100 newtons accelerates a mass of 5 kg for 10 seconds. If
the mass is initially at rest, calculate the final velocity.
Firstly it is necessary to calculate the acceleration.
F = 100 newtons
m = 5 kg
F = ma so a = F/m = 100/5 = 20 m/s2
Next work out the final velocity, knowing the acceleration:
Substitute for u, a and t:
u = initial velocity = 0 since the object is at rest
a = 20 m/s2
t = 10 s
v = u + at = 0 + 20 x 10 = 200 m/s
(2) A mass of 10 kg is dropped from the top of a building which is 100 metres tall. How long does it take to reach the ground?
In
this example, in theory it doesn't make any difference what the value
for the mass is, the acceleration due to gravity is g irrespective of
the mass. Galileo demonstrated this when he dropped two balls of equal
sizes but differing masses from the leaning tower of Pisa. However in
reality, the drag force due to air resistance will slow down the falling
mass, so a 10 kg sheet of timber would fall slower than a 10 kg lead
weight. So assume there is no drag and the calculations apply to a
weight falling in a vacuum.
We know s = 100 m
g = 9.81 m/s2
u = 0 m/s
We can use the equation s = ut + 1/2 at2
The acceleration a in this case is the acceleration due to gravity so a = g
Therefore substituting for u and g gives
s = 0t +1/2 gt2 s = 1/2gt2
Rearranging
t = √(2s/g) = √(2 x 100) / 9.81 = 4.5 seconds approx
Applied Mechanics by John Hannah and MJ Hillier
is a standard text book for students taking Diploma and Technician
courses in engineering. It covers the basic concepts I briefly cover in
this article as well as as other topics such as motion in a circle,
periodic motion, statics and frameworks, impulse and momentum, stress
and strain, bending of beams and fluid dynamics. Worked examples are
included in each chapter in addition to set problems with answers
provided.
Mathematics
Engineering Mathematics by K.A. Stroud
is an excellent math textbook for both engineering students and anyone
with an interest in the subject. The material has been written for part 1
of BSc. Engineering Degrees and Higher National Diploma courses.
A
wide range of topics are covered including matrices, vectors, complex
numbers, calculus, calculus applications, differential equations,
series, probability theory, and statistics. The text is written in the
style of a personal tutor, guiding the reader through the content,
posing questions, and encouraging them to provide the answer.
This book basically makes learning mathematics fun!
References
Hannah, J. and Hillerr, M. J., (1971) Applied Mechanics (First metric ed. 1971) Pitman Books Ltd., London, England.
If you liked this article, you may be interested in reading more articles about mechanics:
This
content is accurate and true to the best of the author’s knowledge and
is not meant to substitute for formal and individualised advice from a
qualified professional.
Gas
turbine engines are used in many applications, not just on aircraft.
They power ships, tanks, helicopters and they're also sometimes used in
power stations to drive alternators (AC generators) for generating
electrical power. Gas turbine engines have been used to power trains in
the 50s and 60s, e.g. the Union Pacific GTEL locomotive. A "jet engine"
is a specific type of gas turbine engine where a jet is used to provide
thrust. The jet can provide thrust directly (turbojet) or power a fan
(turbofan engine) or propeller (turboprop). The advantage of a gas
turbine engine is its high efficiency when scaled up and run at high
power. At small scales (if they were used to power cars) they would be
less efficient than a piston engine. Gas turbine engines also have a
high power to weight ratio compared to a piston engine. Thanks to ChatGPT for drawing a graphic for me.
It took me forever last week to source these. The engineering aspect and excuse to post about them is that they have sealed ball bearings, so somewhat better than the cup and cone bearings used in traditional mountain bike wheels. The latter are a pain in the arse to maintain and water gets into the ones on the back wheel when hosing the sprockets after they get covered with muck. So they have to be dismantled, cleaned and degreased (see photo below). Several local bike shops hadn't heard of these wheels or said they didn't exist. Anyway 360cycles.ie will be getting a good review because they were really helpful and gave lots of updates on the progress of sourcing them for me.
My
bow saw blade is years old. I've cut up loads of logs and full trees
with it and I sharpen it every so often (an extremely boring and tedious
job, because there's probably over a hundred edges to do.) However, it
was binding, because I reckoned, the faces of the teeth were worn and
there was no kerf remaining.
The teeth of a saw blade are alternately set to the left and right, so
that they point slightly away from the blade. This gives the saw a kerf,
making the width of the cut wider than the body of the blade behind the
teeth so the blade doesn't bind. Without a kerf, a blade would stick in
damp timber. I used a saw set tool on the blade (one of several old
hand tools belonging to my grandfather) and it's working beautifully
now, no problem cutting logs up to 5" thick. (Handier than taking out
the chainsaw and good for upper body exercise.)
I
tried using a saw set on a carpenter's hand saw once and it broke one
of the teeth. So I'm wondering can only some modern saws/saw blades be
used with a saw set because the teeth are so hard and the ultimate
strength of the steel isn't much higher than the yield strength. I.e.
once the elastic limit is reached, teeth don't deform plastically and
just break? The engineering aspect of this post is that materials have a
yield strength which is the max strain they can undergo elastically without permanent deformation. After that they deform plastically and don't spring back into shape. The ultimate strength,
measured in units of newtons per square metre or pascals (a pressure
measurement) is the point at which a material will fracture.
Did you know WD-40 isn't specifically a lubricant? Its primary function is as a penetrating oil, for freeing stuck bolts and similar. Waste engine oil is perfectly suitable for hedge cutter blades and garden shears., although probably not good for the environment. It's thicker than light machine oil and so stays longer in contact with metal surfaces, without being squeezed out. Lubrication is a Goldilocks process. The lubricating layer shouldn't be too thin, or surfaces will still rub together, increasing friction. If the layer is too thick, it results in viscous friction, which can cause energy loss and drag on fast moving parts in contact.
At least on some of them. In the trade, these are called traction motors. All of the locomotives on the Irish rail network are
diesel-electric, with engines that run on diesel. However, the engines don't drive the
wheels directly. Instead, they power a generator and the wheels are driven by electric motors.
This makes it easier to control speed using electronics/electrics, rather than controlling
injectors on a diesel engine to vary power. Also, electric motors have full torque at zero RPM,
unlike an engine which has to spin up to suck in fuel to produce power, and has zero torque at
zero RPM. (Interestingly, steam engines also have full torque at zero RPM, because steam
pressure is instantaneously available to power pistons).
Both the 071 and 201 Class locomotives, used for InterCity passenger and freight transport,
use this system. 071 Class locomotives are mainly used for freight operations.
The DART is, of course, electric, and is supplied with power from overhead lines that operate
at 1500 V DC. Electricity is "collected" using pantographs attached to the roofs of
carriages. All the locomotives on the network are diesel-electric, pulling unpowered coaches. Commuter trains are diesel multiple units (DMUs), as are some InterCity trains. A DMU consists of two or more railcars coupled together to form a trainset, with some or all of the cars powered by their own diesel engines and driving cabs at the ends. Multiple trainsets can be coupled together to form a longer train. While DMUs can be diesel-mechanical (i.e. direct-drive), diesel-electric or
diesel-hydraulic, the 22000 Class units, widely used by Iarnród Éireann for commuter and InterCity use, are diesel-hydraulic. Torque is transmitted through a hydraulic fluid in the transmission or gearboxes to drive the wheels on bogies. The 29000 Class units are also diesel-hydraulic.
The new DART+ fleet will use battery-electric carriages, in advance of an extension of the
electrification of lines beyond the Greater Dublin area. These are known as BEMUs
(Battery Electric Multiple Units). On the Dublin-Cork line, electrification will extend to
Hazelhatch & Celbridge. 155 of the 185 carriages on order are battery-electric, and a
five-carriage train has a battery capacity of 840 kWh and a range of up to 80 km.
These batteries are charged by regenerative braking and also "replenished via fast charging
stations at chosen terminus locations". According to Iarnród Éireann, charging infrastructure
is currently under construction.
More info on the DART+ Programme
here.
Table 1. Locomotive and DMU classes and their uses on the Irish rail network
Back
of envelope calculations suggests a 760 N (approximately 76 kg) load on
poles for force 10 winds, which doesn't seem like much. But that's for
average wind speed. I've asked Kildare Weather have they any recorded
gust speeds. Forces increase exponentially with wind velocity. So
doubling the wind speed quadruples the load. Presumably poles break when
they're rotten at the base and I would think "healthy" poles are
unlikely to fail under normal circumstances unless there's a split in
the timber.
Edit:
Kildare Weather have come back to me with a figure of 85 km/h for Naas
and 95 km/h for Maynooth. (Both gust speeds). The latter figure gives a
load of 710 N or 72 kg. (For a flat surface. There's probably a factor
in the force calculation for round profile objects). Poles are fixed at
one end. I.e They're cantilevered. The wind load spread over a pole
creates a torque at the base of the pole equal to half the force on the
pole multiplied by its length (are poles longer than around 7 m above
ground?)
Did
you know that the force of wind on a surface depends on the square of
the velocity? So if wind speed doubles, the force quadruples. If speed
triples, the force is nine times greater and so on. Since pressure
equals force divided by area, it also follows a square law.
For a jet hitting a surface (doesn't matter what the jet is made of: air, water etc), the force of the jet in newtons is:
F = ρAv²
where ρ is the density of the fluid in kg/m³
A is the cross-sectional area of the jet in m²
and v is the velocity in m/s
The higher the velocity of the fluid, the greater the force. (Think of your pressure washer jet hitting a surface).
What's a "newton"?
It's the SI (Système International d'Unités)
unit of force. A force of 1 newton (1 N) exerted on a mass of 1 kg will give it an
acceleration of 1 m/s². (i.e. the velocity of the mass increases by 1
m/s every second). While all objects have mass, measured in kilos, the force exerted on them by gravity is known as weight. In common usage, we measure weight in kilograms, just like we do for mass, but it is more correctly specified in newtons, the unit of force. To get an idea of the magnitude of 1 newton, it's approximately equal to the force exerted on your hand when a 100 gram weight rests on your palm. While mass stays constant, weight varies and for instance on the Moon, the weight of an object is less.
Did
you know The Spire in Dublin has a shock absorber? Technically these
are called dampers and your car and even your washing machine has them
to reduce vibrations. Dampers are also used on doors, cupboard drawers
and even toilet seats to slow their movement. Many large structures such
as bridges need dampers to reduce oscillations caused by wind or
vehicular traffic.
Resonance
All
objects have a natural frequency that they tend to vibrate at. The
phenomenon is called resonance and that's how musical instruments work. A
column of air in an organ, string on a guitar or bell will vibrate or
oscillate at its natural frequency when struck, plucked or vibrated
using a reed. If you blow over the mouth of a bottle, the air inside
vibrates at a certain pitch. Resonance frequency depends on several
factors including physical dimensions, speed of sound in air and mass of
the object that's resonating. So in an organ or piano, the longest
pipes or strings respectively give the lowest notes. Large structures
can resonate due to strong winds and eventually the oscillations can
build, ultimately leading to destruction of the structure. (Think of
pushing a child on a swing and pushing at the right moment causes the
swing to extend further and further).
What's a damper?
Dampers are used to reduce oscillations so that they continue to decrease in size and die out.
A
mechanical damper is typically a cylinder with a piston and also an
external coil spring. The viscous damper is connected to the object
being damped. As the piston slides along the cylinder, filled with air
or oil, viscous friction slows it's movement, converting the energy of
the oscillating object into heat and reducing the amplitude of
oscillations and causing them to decrease in amplitude.
The Spire of Dublin
The
Spire in Dublin is a 120 m tall structure and to reduce potentially
damaging oscillations, a damper is built inside its structure. The
reciprocal of resonance frequency is the period. This is the length of
time it takes to do one complete oscillation. So if a guitar string
vibrates 100 times a second (100 Hz), the period of the oscillation is
1/100 = 10 mS. The period of The Spire has been analysed as 3.65
seconds. That means when it's oscillating, it sways backwards and
forwards once every 3.65 S. To absorb the oscillations and damp them
out, the damper was tuned to this frequency. It consists of two large
masses, 2 tonne weight in total, attached to the inside of the structure
by viscous dampers. You can read more in this article.
I’m reading Chapter 8, “The Human Touch” of Irish physicist Laurie Winkless’s book Sticky: The Secret Science of Surfaces.
In
2014, I was doing a spot of gardening at the entrance into my house.
The Virginia creeper growing along the wall had covered over the gate
pier and was threatening to swallow the gate as well, so it was time to
get it back under control. I started to cut it back with a secateurs and
after a few minutes of snipping, I ended up on autopilot: snip, pull
back, snip pull back, while thinking about other things and losing
concentration. I lost visual contact with the secateurs under a clump of
vegetation just as a car blew its horn on the road. I looked up while
doing one more snip, and felt a dart of sensation, but strangely not
intense pain. (Like those stories of people having their leg bitten off
by a shark and not being in agony straight away). Realising immediately
what I had done, I was terrified of looking down to see what damage I
had caused. “Luckily”, I had only cut a piece off the tip of my
forefinger the size of half a baked bean, Gross alert! (which I
recovered later that day). I went into survival mode straight away. I
wrapped my finger in kitchen towel and made my way down to my GP’s
clinic. They said they couldn’t do anything with it, and gave me a
letter for A&E. Someone gave me a lift into Naas Hospital and after a
short wait, an emergency technician dealt with the wound. First they
gave me several anaesthetic injections in my finger (not pleasant) and
then irrigated the open wound (which was equally unpleasant and
uncomfortable). Maybe it hadn’t fully kicked in, but the anaesthetic
only seemed to work on pain nerves and not all the other types of
sensors and nerves in skin that are sensitive to touch, temperature,
pressure etc.) To cut a long story short, my finger totally recovered
after a few weeks and even though I had completely lost the top of it
and the fingerprints, it magically regrew, complete with prints. It’s
still a little bit sensitive when I touch things (with a slightly
uncomfortable sensation like when you hit your “funny bone”, presumably
due to raw nerve endings), but not something I consciously think about.
In the chapter of Laurie Winkless’s book about skin, we learn how it’s
a sense that’s unappreciated in its complexity and ability to detect
many different sensations. We can also detect roughness on surfaces only
a few atoms thick and fingerprints apparently have “roots”, which allow
them to grow, luckily for me.
They
began as steam or drop hammers, first used in the 1840s for forging
large components or driving piles. Steam was used to raise the hammer
which was then dropped. Hydraulic presses take a more gentle and less
noisy approach, slowly squeezing white hot pieces of steel which can be
massive. They also put less stress on the material being forged, shaping
it uniformly and reducing the likelihood of flaws. Steam hammers are
still used for pile driving.
I could look at steam trains all day. No.
131 isn't the oldest locomotive in the RPSI's collection of vintage
steam trains. That honour goes to No. 186 which was built in the 1880s
and worked as a goods engine but also on passenger trains. Her last
operation was hauling beet in 1962/63.
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