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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.

We have discussed that when an object rests on a horizontal surface, there is a normal force supporting it equal in magnitude to its weight. Furthermore, simple friction is always proportional to the normal force.

Making connections: submicroscopic explanations of friction

The simpler aspects of friction dealt with so far are its macroscopic (large-scale) characteristics. Great strides have been made in the atomic-scale explanation of friction during the past several decades. Researchers are finding that the atomic nature of friction seems to have several fundamental characteristics. These characteristics not only explain some of the simpler aspects of friction—they also hold the potential for the development of nearly friction-free environments that could save hundreds of billions of dollars in energy which is currently being converted (unnecessarily) to heat.

Questions & Answers

Given that the elasticity of supply for a good is 2 and the percentage change in price is 45%.What is the percentage change in quantity supplied
Mbe Reply
state and explainfour function of a costumer service
Egba Reply
the circular flow model of the economy is a simplification showing how the economy works and the relationship between income,production and spending in the economy as a whole
Anna Reply
what is circular flow
Ntokozo Reply
what is economics?
Dorcas Reply
Economics is defined as the science that study human behaviour as a relationship between ends and scarce means which have alternative uses.
Emmanuella
economics is a social science concerned with the production,distribution, and consumption of goods and services
Michael
in 2021 Amazon reduced the annual subscription fee for its prime membership service which provides free two_day shipping on many goods and other benefits, from $119 to $99. Zoppa consulting, an investment firm estimated that before the price reduction, prime had 62million subscribers globally. If so, what is the arc elasticity of demand for a prime membership.
Joan Reply
Differences between microeconomics and macroeconomics
tatiana Reply
Macroeconomics deal with the economy as a whole.that is an economy affect the firm ,government and the households eg.unemployment, whilst Microeconomics deal with the the decision making of households,firm and government separately.
Amah
what is Economics
Ebem Reply
the branch of knowledge concerned with the production, consumption, and transfer of wealth and has Influence by sociology!!!!
Ajay
Economics is the study of how humans make decisions when they want to fulfil their requirements and desires for goods, services and resources.
Abdullah
Economics is the study how humans make decisions in the faces of scarcity.
Rose
economic is the study of how human make decision in the fact of scarcity.
Toang
Economics is a social science which study human behavior as a relationship between earn and scarce mean which have alternative uses
Juliet
what is market structure
Fatima
market structure in economics depicts how firms are differentiated and categorised based on types of goods they sell and how their operations are affected by external factors and elements.
Nasir
what is economic theory
Madara
what is demand
Gooluck Reply
demand is the willingness to purchase something
Mohamed
demand is the potential ability or williness to purchases something at a particular price at a given period of time..
Ahmed
Demand refers to as quantities of a goods and services in which consumers are willing and able to purchase at a given period of time. Demand can also be defined as the desire backed by ability to purchase .
Fadiga
what is demand
John Reply
is the production of goods in scarcity
David
thanks
John
Demand refers to as quantities of a goods and services in which consumers are willing and able to purchase at a given period of time.
Fadiga
Demand refers to the quantity of goods and services that a consumer is willing and able to buy at a given price over a period of time
Augustina
Do high interest rate in a country increase investment
Alfred
what is demand of supply
music Reply
What is the meaning of supply of labour
Anthonia Reply
what is production?
Elizabeth Reply
Production is basically the creation of goods and services to satisfy human wants
Anthonia
importance of tertiary and example
Elizabeth
Production is the process of producing goods and services to satisfy human needs and want.
Augustina
under what condition will demand curve slope upward from left to right instead of normally sloping downward from left to right
Atama Reply
how i can calculate elasticity?
Tewekel Reply
A soccer field is a rectangle 130 meters wide and 110 meters long. The coach asks players to run from one corner to the other corner diagonally across. What is that distance, to the nearest tenths place.
Kimberly Reply
Jeannette has $5 and $10 bills in her wallet. The number of fives is three more than six times the number of tens. Let t represent the number of tens. Write an expression for the number of fives.
August Reply
What is the expressiin for seven less than four times the number of nickels
Leonardo Reply
How do i figure this problem out.
how do you translate this in Algebraic Expressions
linda Reply
why surface tension is zero at critical temperature
Shanjida
I think if critical temperature denote high temperature then a liquid stats boils that time the water stats to evaporate so some moles of h2o to up and due to high temp the bonding break they have low density so it can be a reason
s.
Need to simplify the expresin. 3/7 (x+y)-1/7 (x-1)=
Crystal Reply
. After 3 months on a diet, Lisa had lost 12% of her original weight. She lost 21 pounds. What was Lisa's original weight?
Chris Reply
Difference between extinct and extici spicies
Amanpreet Reply
While the American heart association suggests that meditation might be used in conjunction with more traditional treatments as a way to manage hypertension
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Source:  OpenStax, Concepts of physics. OpenStax CNX. Aug 25, 2015 Download for free at https://legacy.cnx.org/content/col11738/1.5
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