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Take-home experiment

Find a small plastic object (such as a food container) and slide it on a kitchen table by giving it a gentle tap. Now spray water on the table, simulating a light shower of rain. What happens now when you give the object the same-sized tap? Now add a few drops of (vegetable or olive) oil on the surface of the water and give the same tap. What happens now? This latter situation is particularly important for drivers to note, especially after a light rain shower. Why?

Many people have experienced the slipperiness of walking on ice. However, many parts of the body, especially the joints, have much smaller coefficients of friction—often three or four times less than ice. A joint is formed by the ends of two bones, which are connected by thick tissues. The knee joint is formed by the lower leg bone (the tibia) and the thighbone (the femur). The hip is a ball (at the end of the femur) and socket (part of the pelvis) joint. The ends of the bones in the joint are covered by cartilage, which provides a smooth, almost glassy surface. The joints also produce a fluid (synovial fluid) that reduces friction and wear. A damaged or arthritic joint can be replaced by an artificial joint ( [link] ). These replacements can be made of metals (stainless steel or titanium) or plastic (polyethylene), also with very small coefficients of friction.

Two X-x rays of an artificial knee replacement are shown.
Artificial knee replacement is a procedure that has been performed for more than 20 years. In this figure, we see the post-op x rays of the right knee joint replacement. (credit: Mike Baird, Flickr)

Other natural lubricants include saliva produced in our mouths to aid in the swallowing process, and the slippery mucus found between organs in the body, allowing them to move freely past each other during heartbeats, during breathing, and when a person moves. Artificial lubricants are also common in hospitals and doctor’s clinics. For example, when ultrasonic imaging is carried out, the gel that couples the transducer to the skin also serves to to lubricate the surface between the transducer and the skin—thereby reducing the coefficient of friction between the two surfaces. This allows the transducer to mover freely over the skin.

Skiing exercise

A skier with a mass of 62 kg is sliding down a snowy slope. Find the coefficient of kinetic friction for the skier if friction is known to be 45.0 N.

Strategy

The magnitude of kinetic friction was given in to be 45.0 N. Kinetic friction is related to the normal force N size 12{N} {} as f k = μ k N size 12{f rSub { size 8{k} } =μ rSub { size 8{k} } N} {} ; thus, the coefficient of kinetic friction can be found if we can find the normal force of the skier on a slope. The normal force is always perpendicular to the surface, and since there is no motion perpendicular to the surface, the normal force should equal the component of the skier’s weight perpendicular to the slope. (See the skier and free-body diagram in [link] .)

The figure shows a skier going down a slope that forms an angle of 25 degrees with the horizontal. The weight of the skier, labeled w, is represented by a red arrow pointing vertically downward. This weight is divided into two components, w perpendicular is perpendicular to the slope, and w parallel is parallel to the slope. The normal force, labeled N, is also perpendicular to the slope, equal in magnitude but opposite in direction to w perpendicular. The friction, f, is represented by a red arrow pointing upslope. In addition, the figure shows a free body diagram that shows the relative magnitudes and directions of w, f, and N.
The motion of the skier and friction are parallel to the slope and so it is most convenient to project all forces onto a coordinate system where one axis is parallel to the slope and the other is perpendicular (axes shown to left of skier). N (the normal force) is perpendicular to the slope, and f (the friction) is parallel to the slope, but w (the skier’s weight) has components along both axes, namely w and W // . N is equal in magnitude to w , so there is no motion perpendicular to the slope. However, f is less than W // in magnitude, so there is acceleration down the slope (along the x -axis).

Questions & Answers

distinguish between anatomy and physiology
Amina Reply
Anatomy is the study of internal structure of an organism while physiology is the study of the function/relationship of the body organs working together as a system in an organism.
adeyeye
distinguish between anatomy and physiology
Erny Reply
regional anatomy is the study of the body regionally
Ismail Reply
what is the meaning of regional anatomy
Aminat Reply
epithelial tissue: it covers the Hollow organs and body cavities
Esomchi Reply
in short way what those epithelial tissue mean
Zainab Reply
in short way what those epithelial tissue mean
Chizoba
What is the function of the skeleton
Lilias Reply
movement
Ogar
Locomotion
Ojo
support
Aishat
and body shape/form
Aishat
what is homeostasis?
Samuel Reply
what's physiology
AminchiSunday Reply
what is physiology
AminchiSunday
physically is the study of the function of the body
Najaatu
that is what I want ask
YAU
u are wright
YAU
pls what are the main treatment of hiccups
YAU
physiology is the study of the function of the body
Najaatu
hiccups happen when something irritates the nerves that course your diaphragm to contract
Najaatu
how did hypothalamus manege to control all activities of the various hormones
malual
what is protein
Abdulsalam
how can I treat pain a patient feels after eating meals
Namuli Reply
how do I treat a three year old baby of skin infection?
Okocha Reply
It depends on the type of infection. Bacterial, fungal, parasitic or viral?
schler
if you can share the sign ad symptoms of the skin infection then u geh the treatment cox they're different sign ad symptoms of skin infection with different treatment
Sa
the sign and symptoms of maleria
Abdulsalam
prostaglandin and fever
Maha Reply
yes
rayyanu
welcome sir
rayyanu
prostaglandin E2 is the final mediator.
Lemlem
prostaglandin E2 is the final mediator of fever.
Lemlem
yes
Agabi
good evening
Jediel
tissue.
Akoi
explain
Chizoba
Hi
Anya
,good evening
Anya
Discuss the differences between taste and flavor, including how other sensory inputs contribute to our  perception of flavor.
John Reply
taste refers to your understanding of the flavor . while flavor one The other hand is refers to sort of just a blend things.
Faith
While taste primarily relies on our taste buds, flavor involves a complex interplay between taste and aroma
Kamara
which drugs can we use for ulcers
Ummi Reply
omeprazole
Kamara
what
Renee
what is this
Renee
is a drug
Kamara
of anti-ulcer
Kamara
Omeprazole Cimetidine / Tagament For the complicated once ulcer - kit
Patrick
what is the function of lymphatic system
Nency Reply
Not really sure
Eli
to drain extracellular fluid all over the body.
asegid
The lymphatic system plays several crucial roles in the human body, functioning as a key component of the immune system and contributing to the maintenance of fluid balance. Its main functions include: 1. Immune Response: The lymphatic system produces and transports lymphocytes, which are a type of
asegid
to transport fluids fats proteins and lymphocytes to the blood stream as lymph
Adama
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Source:  OpenStax, College physics: physics of california. OpenStax CNX. Sep 30, 2013 Download for free at http://legacy.cnx.org/content/col11577/1.1
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