Friction is a force that opposes the relative motion between two surfaces in contact. There are four main types of friction: sliding friction, which acts when an object slides along a surface; static friction, which prevents stationary objects from moving; fluid friction, which acts on objects moving through fluids like air or water; and rolling friction, which occurs when a round object like a wheel rolls along a surface. Friction can be useful to enable motion like in walking or driving, but it also leads to wasted energy as heat and additional force needed to overcome it. Lubricants are used to reduce friction in machines.
Friction is a force that slows down moving objects or prevents stationary objects from moving .
Friction is a contact force .
Friction produces heat .
For example – A matchstick
Friction opposes the motion of an object
When one surface moves over another , these grooves and ridges get caught up with each other and slow down the motion . This causes friction .
Friction is a force that slows down moving objects or prevents stationary objects from moving .
Friction is a contact force .
Friction produces heat .
For example – A matchstick
Friction opposes the motion of an object
When one surface moves over another , these grooves and ridges get caught up with each other and slow down the motion . This causes friction .
Friction is known as the resistance to motion of one object moving relative to another. According to scientists it is the result of the electromagnetic attraction between charged particles in two touching surfaces.
Best ppt on friction explaination, types of friction ,advantage & disadvantage of friction.effects of friction, methods of increacing and reducing friction,with example
Kinds of Friction
A moving object is affected by friction. However, the amount of friction may vary depending on the type of surface the object gets in contact with.
Rolling Friction
When an object rolls over a surface , rolling friction is produced. One of the most common examples of rolling friction is the movement of motor vehicle tires on the road , a process that generates heat and sound as by-products. Rolling friction is easier to overcome than sliding friction for similar materials. This type of friction is important to engineers who design certain products. For example, skates, skateboards, and bicycles need wheels that move freely.
Sliding Friction
Sliding friction occurs when two solid surfaces slide over each other. Sliding friction can be useful. For example, you can spread sand on an icy path to improve your footing. Ballet dancers apply a sticky powder to the soles of their ballet slippers so they won’t slip on the dance floor. And when you stop a bicycle with hand brakes, rubber pads slide against the tire surfaces, causing the wheels to slow and eventually stop. On the other hand, sliding friction is a problem if you fall off your bike and skin your knee!
Fluid Friction
Fluids, such as water, oil, or air, are materials that flow easily. Fluid friction occurs when a solid object moves through a fluid. Like rolling friction, fluid friction is easier to overcome than sliding friction.
Static Friction
The friction that acts on objects that are not moving is called static friction. Because of static friction, you must use extra force to start the motion of stationary objects. For example, think about what happens when you try to push a heavy desk across a floor. If you push on the desk with a force less than the force of static friction between the desk and the floor, the desk will not move. To make the desk move, you must exert a force greater than the force of static friction.
Introduction:
RNA interference (RNAi) or Post-Transcriptional Gene Silencing (PTGS) is an important biological process for modulating eukaryotic gene expression.
It is highly conserved process of posttranscriptional gene silencing by which double stranded RNA (dsRNA) causes sequence-specific degradation of mRNA sequences.
dsRNA-induced gene silencing (RNAi) is reported in a wide range of eukaryotes ranging from worms, insects, mammals and plants.
This process mediates resistance to both endogenous parasitic and exogenous pathogenic nucleic acids, and regulates the expression of protein-coding genes.
What are small ncRNAs?
micro RNA (miRNA)
short interfering RNA (siRNA)
Properties of small non-coding RNA:
Involved in silencing mRNA transcripts.
Called “small” because they are usually only about 21-24 nucleotides long.
Synthesized by first cutting up longer precursor sequences (like the 61nt one that Lee discovered).
Silence an mRNA by base pairing with some sequence on the mRNA.
Discovery of siRNA?
The first small RNA:
In 1993 Rosalind Lee (Victor Ambros lab) was studying a non- coding gene in C. elegans, lin-4, that was involved in silencing of another gene, lin-14, at the appropriate time in the
development of the worm C. elegans.
Two small transcripts of lin-4 (22nt and 61nt) were found to be complementary to a sequence in the 3' UTR of lin-14.
Because lin-4 encoded no protein, she deduced that it must be these transcripts that are causing the silencing by RNA-RNA interactions.
Types of RNAi ( non coding RNA)
MiRNA
Length (23-25 nt)
Trans acting
Binds with target MRNA in mismatch
Translation inhibition
Si RNA
Length 21 nt.
Cis acting
Bind with target Mrna in perfect complementary sequence
Piwi-RNA
Length ; 25 to 36 nt.
Expressed in Germ Cells
Regulates trnasposomes activity
MECHANISM OF RNAI:
First the double-stranded RNA teams up with a protein complex named Dicer, which cuts the long RNA into short pieces.
Then another protein complex called RISC (RNA-induced silencing complex) discards one of the two RNA strands.
The RISC-docked, single-stranded RNA then pairs with the homologous mRNA and destroys it.
THE RISC COMPLEX:
RISC is large(>500kD) RNA multi- protein Binding complex which triggers MRNA degradation in response to MRNA
Unwinding of double stranded Si RNA by ATP independent Helicase
Active component of RISC is Ago proteins( ENDONUCLEASE) which cleave target MRNA.
DICER: endonuclease (RNase Family III)
Argonaute: Central Component of the RNA-Induced Silencing Complex (RISC)
One strand of the dsRNA produced by Dicer is retained in the RISC complex in association with Argonaute
ARGONAUTE PROTEIN :
1.PAZ(PIWI/Argonaute/ Zwille)- Recognition of target MRNA
2.PIWI (p-element induced wimpy Testis)- breaks Phosphodiester bond of mRNA.)RNAse H activity.
MiRNA:
The Double-stranded RNAs are naturally produced in eukaryotic cells during development, and they have a key role in regulating gene expression .
Richard's entangled aventures in wonderlandRichard Gill
Since the loophole-free Bell experiments of 2020 and the Nobel prizes in physics of 2022, critics of Bell's work have retreated to the fortress of super-determinism. Now, super-determinism is a derogatory word - it just means "determinism". Palmer, Hance and Hossenfelder argue that quantum mechanics and determinism are not incompatible, using a sophisticated mathematical construction based on a subtle thinning of allowed states and measurements in quantum mechanics, such that what is left appears to make Bell's argument fail, without altering the empirical predictions of quantum mechanics. I think however that it is a smoke screen, and the slogan "lost in math" comes to my mind. I will discuss some other recent disproofs of Bell's theorem using the language of causality based on causal graphs. Causal thinking is also central to law and justice. I will mention surprising connections to my work on serial killer nurse cases, in particular the Dutch case of Lucia de Berk and the current UK case of Lucy Letby.
A brief information about the SCOP protein database used in bioinformatics.
The Structural Classification of Proteins (SCOP) database is a comprehensive and authoritative resource for the structural and evolutionary relationships of proteins. It provides a detailed and curated classification of protein structures, grouping them into families, superfamilies, and folds based on their structural and sequence similarities.
Earliest Galaxies in the JADES Origins Field: Luminosity Function and Cosmic ...Sérgio Sacani
We characterize the earliest galaxy population in the JADES Origins Field (JOF), the deepest
imaging field observed with JWST. We make use of the ancillary Hubble optical images (5 filters
spanning 0.4−0.9µm) and novel JWST images with 14 filters spanning 0.8−5µm, including 7 mediumband filters, and reaching total exposure times of up to 46 hours per filter. We combine all our data
at > 2.3µm to construct an ultradeep image, reaching as deep as ≈ 31.4 AB mag in the stack and
30.3-31.0 AB mag (5σ, r = 0.1” circular aperture) in individual filters. We measure photometric
redshifts and use robust selection criteria to identify a sample of eight galaxy candidates at redshifts
z = 11.5 − 15. These objects show compact half-light radii of R1/2 ∼ 50 − 200pc, stellar masses of
M⋆ ∼ 107−108M⊙, and star-formation rates of SFR ∼ 0.1−1 M⊙ yr−1
. Our search finds no candidates
at 15 < z < 20, placing upper limits at these redshifts. We develop a forward modeling approach to
infer the properties of the evolving luminosity function without binning in redshift or luminosity that
marginalizes over the photometric redshift uncertainty of our candidate galaxies and incorporates the
impact of non-detections. We find a z = 12 luminosity function in good agreement with prior results,
and that the luminosity function normalization and UV luminosity density decline by a factor of ∼ 2.5
from z = 12 to z = 14. We discuss the possible implications of our results in the context of theoretical
models for evolution of the dark matter halo mass function.
What is greenhouse gasses and how many gasses are there to affect the Earth.moosaasad1975
What are greenhouse gasses how they affect the earth and its environment what is the future of the environment and earth how the weather and the climate effects.
Richard's aventures in two entangled wonderlandsRichard Gill
Since the loophole-free Bell experiments of 2020 and the Nobel prizes in physics of 2022, critics of Bell's work have retreated to the fortress of super-determinism. Now, super-determinism is a derogatory word - it just means "determinism". Palmer, Hance and Hossenfelder argue that quantum mechanics and determinism are not incompatible, using a sophisticated mathematical construction based on a subtle thinning of allowed states and measurements in quantum mechanics, such that what is left appears to make Bell's argument fail, without altering the empirical predictions of quantum mechanics. I think however that it is a smoke screen, and the slogan "lost in math" comes to my mind. I will discuss some other recent disproofs of Bell's theorem using the language of causality based on causal graphs. Causal thinking is also central to law and justice. I will mention surprising connections to my work on serial killer nurse cases, in particular the Dutch case of Lucia de Berk and the current UK case of Lucy Letby.
Multi-source connectivity as the driver of solar wind variability in the heli...Sérgio Sacani
The ambient solar wind that flls the heliosphere originates from multiple
sources in the solar corona and is highly structured. It is often described
as high-speed, relatively homogeneous, plasma streams from coronal
holes and slow-speed, highly variable, streams whose source regions are
under debate. A key goal of ESA/NASA’s Solar Orbiter mission is to identify
solar wind sources and understand what drives the complexity seen in the
heliosphere. By combining magnetic feld modelling and spectroscopic
techniques with high-resolution observations and measurements, we show
that the solar wind variability detected in situ by Solar Orbiter in March
2022 is driven by spatio-temporal changes in the magnetic connectivity to
multiple sources in the solar atmosphere. The magnetic feld footpoints
connected to the spacecraft moved from the boundaries of a coronal hole
to one active region (12961) and then across to another region (12957). This
is refected in the in situ measurements, which show the transition from fast
to highly Alfvénic then to slow solar wind that is disrupted by the arrival of
a coronal mass ejection. Our results describe solar wind variability at 0.5 au
but are applicable to near-Earth observatories.
Comparing Evolved Extractive Text Summary Scores of Bidirectional Encoder Rep...University of Maribor
Slides from:
11th International Conference on Electrical, Electronics and Computer Engineering (IcETRAN), Niš, 3-6 June 2024
Track: Artificial Intelligence
https://www.etran.rs/2024/en/home-english/
2. WHAT IS FRICTION ?
We have learnt that a force is required to stop the movement of
the body in motion. Then why doesn’t a swing not continue to
move forever once you have given it a push? Or why does a ball
not roll endlessly once you have kicked it , even if no force is
applied to stop it? This is because of friction.
Friction is a force that opposes motion between two surfaces that
are touching. Frictional force always opposes motion, trying to
stop the movement of one surface over another.
3. SURFACE TEXTURE
For friction the object moving should touch the surface ,then
only there comes a frictional force. So a surface plays a very
important role in frictional force. Surfaces can be smooth or
rough.
The smoother the surface is ,the lesser is the frictional force.
That is a why a ball travels a great distance over a tiled floor
than a carpeted floor.
4. TYPES OF FRICTION
There are 4 types of friction:
sliding Friction static friction
Fluid friction Rolling Friction
5. SLIDING FRICTION
The minimum force required to make a body just to slide over
the surface is called sliding reflection. Once a body starts
sliding the sliding friction is reduced. It is less than static
friction. It is the rubbing of bodies in sliding contact.
Let’s take an example when a person is skiing through on the
mountains, then it is a sliding friction.
.
6. STATIC FRICTION
When a force is applied on an object to move it but it doesn’t
moves, as the force applied is balanced by the force of static
friction, then this is called static friction. It ends with the
beginning of sliding of the object at rest.
A simple example for static friction is a wooden block kept on a
table. Unless sufficient force is exerted, the block will not
slide down the table because static friction holds it place
and resists sliding.
7. FLUID FRICTION
The friction caused by an object moving through something that
engulfs it in a fluid. It opposes motion between objects
traveling through fluids like air and water.
A simple example for fluid friction is Air resistance and a
swimmer swimming through water exhibits fluid friction.
8. ROLLING FRICTION
It is the resistance that occurs when a round object such as a
ball or tire rolls on a flat surface. It is mainly caused by the
deformation of the object , the deformation of the surface or
both. Rolling Friction is much less than the sliding friction.
A simple example for rolling friction is a car with its wheels
moving or the roller skates which we use for skating.
9. LUBRICANTS
A lubricant is a substance introduced between two moving
surfaces to reduce the friction between them, improving its
efficiency and reducing the wear. Lubricants include motor
oil, wax, grease etc.
A simple example for the use of lubricants is that machine are
oiled from time to time to reduce the friction.
Wax Oil
10. INCREASING FRICTION
•There are many situations when we cannot do
without Friction. To overcome skidding along a
slippery surface we adopt measures to increase
friction.
•Kutcha roads get muddy and slippery during
rains. It is not possible to walk or drive on such
roads. For this sand and gravel are spread over
the mud to make the road rough.
•Tyres of our vehicles and also soles of the
shoes are grooved. This increases friction. This
helps easy rolling of vehicles on the road and
also provides better gripping with shoes on
floor.
•Mountaineers also wear spiked shoes to
increase friction while walking on snow.
11. Reducing Friction
•Friction is reduced when the area of contact between the
two rubbing surfaces is reduced. This is done with the
help of rollers. Wheels of the rollers not only reduce the
area of contact between two surfaces but also move
smoothly.
•Making the surfaces smooth also reduces friction, like
cemented roads are more smoother than rough roads so it
reduces friction.
•Lubrication also helps in reducing friction.
12. WHY FRICTION IS NECESSARY? OR ITS
ADVANTAGES
Friction is very necessary in our daily life. Friction helps us in
walking conveniently. It saves us from slipping on a smooth
and slippery surface.
It also helps us in writing on piece of paper. It is not possible to
draw or write on oily or butter paper.
The moving and stopping of vehicles on the road also depends
on friction.
It is also helpful in eating or drinking something as it helps us
to hold the food or drink in our hand.
It is also helps us in lighting a match-stick by rubbing it along
the rough surface on the sides of match-box.
Like these there are many examples of it which are very
necessary in our daily life.
13. WHEN FRICTION IS HARMFUL? OR ITS
DISADVANTAGES
As you know that friction is very important but it is very harmful
too. As it acts all the time so it reduces the speed of the
body in motion. For this additional force has to be applied
from time to time to maintain motion and speed. For this,
more energy or fuel is consumed so it results in the waste of
energy.
An object in motion over a surface gets heated on running at a
speed and for a long distance. For this we have to adopt the
cooling systems. Sometimes even the fire accidents in cars
and trains take place because of too much frictional force.
So even if friction is very helpful for us, it is dangerous too that
is why it is also called necessary evil.
