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Section summary

  • Statics plays an important part in understanding everyday strains in our muscles and bones.
  • Many lever systems in the body have a mechanical advantage of significantly less than one, as many of our muscles are attached close to joints.
  • Someone with good posture stands or sits in such as way that their center of gravity lies directly above the pivot point in their hips, thereby avoiding back strain and damage to disks.

Conceptual questions

Why are the forces exerted on the outside world by the limbs of our bodies usually much smaller than the forces exerted by muscles inside the body?

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Explain why the forces in our joints are several times larger than the forces we exert on the outside world with our limbs. Can these forces be even greater than muscle forces?

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Certain types of dinosaurs were bipedal (walked on two legs). What is a good reason that these creatures invariably had long tails if they had long necks?

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Swimmers and athletes during competition need to go through certain postures at the beginning of the race. Consider the balance of the person and why start-offs are so important for races.

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If the maximum force the biceps muscle can exert is 1000 N, can we pick up an object that weighs 1000 N? Explain your answer.

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Suppose the biceps muscle was attached through tendons to the upper arm close to the elbow and the forearm near the wrist. What would be the advantages and disadvantages of this type of construction for the motion of the arm?

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Explain one of the reasons why pregnant women often suffer from back strain late in their pregnancy.

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Problems&Exercises

Verify that the force in the elbow joint in [link] is 407 N, as stated in the text.

F B = 470 N; r 1 = 4.00 cm; w a = 2.50 kg; r 2 = 16.0 cm; w b = 4.00 kg; r 3 = 38.0 cm F E = w a r 2 r 1 1 + w b r 3 r 1 1 = 2.50 kg 9.80 m / s 2 16.0 cm 4.0 cm 1 + 4.00 kg 9.80 m / s 2 38.0 cm 4.00 cm 1 = 407 N alignl { stack { size 12{F rSub { size 8{B} } ="470"" N ; "r rSub { size 8{1} } =4 cdot "00"" cm ; "w rSub { size 8{a} } =2 cdot "50"" kg ;"} {} #r rSub { size 8{2} } ="16" cdot 0" cm ;" {} # w rSub { size 8{b} } =4 cdot "00"" kg ; "r rSub { size 8{3} } ="38" cdot 0" cm" {} #F rSub { size 8{E} } times r rSub { size 8{1} } =w rSub { size 8{a} } left ( { {r rSub { size 8{2} } } over {r rSub { size 8{1} } } } - 1 right )+w rSub { size 8{b} } left ( { {r rSub { size 8{3} } } over {r rSub { size 8{1} } } } - 1 right ) {} # = left (2 cdot "50 kg" right ) left (9 cdot "80 " {m} slash {s rSup { size 8{2} } } right ) left ( { {"16" cdot "0 cm"} over {4 cdot "0 cm"} } - 1 right ) {} #+ left (4 cdot "00 kg" right ) left (9 cdot "80 " {m} slash {s rSup { size 8{2} } } right ) left ( { {"38" cdot "0 cm"} over {4 cdot "00 cm"} } - 1 right ) {} # = {underline {"407"" N"}} {}} } {}

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Two muscles in the back of the leg pull on the Achilles tendon as shown in [link] . What total force do they exert?

An Achilles tendon is shown in the figure. A vertical dotted line is shown at the middle of the top part. Two vectors inclined at twenty degree each with respect to the vertical dotted line are shown.
The Achilles tendon of the posterior leg serves to attach plantaris, gastrocnemius, and soleus muscles to calcaneus bone.
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The upper leg muscle (quadriceps) exerts a force of 1250 N, which is carried by a tendon over the kneecap (the patella) at the angles shown in [link] . Find the direction and magnitude of the force exerted by the kneecap on the upper leg bone (the femur).

The figure shows a side view of the bones of a knee and the quadriceps muscle. The upper bone is inclined at fifty five degrees to the horizontal and the tension exerted by the quadriceps muscle is one thousand two hundred and fifty newtons. The tendon from the knee cap to the lower bone is inclined at seventy five degrees below the horizontal. The force in this direction is the same as that provided by the quadriceps.
The knee joint works like a hinge to bend and straighten the lower leg. It permits a person to sit, stand, and pivot.

1.1 × 10 3 N θ = 190 º ccw from positive x axis alignl { stack { size 12{1 "." 1 times "10" rSup { size 8{3} } `N} {} #θ="190"°`"ccw"`"from"`"positive"`x`"axis" {} } } {}

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A device for exercising the upper leg muscle is shown in [link] , together with a schematic representation of an equivalent lever system. Calculate the force exerted by the upper leg muscle to lift the mass at a constant speed. Explicitly show how you follow the steps in the Problem-Solving Strategy for static equilibrium in Applications of Statistics, Including Problem-Solving Strategies .

A machine for leg exercise is shown. A wire is tied to a cuff around the lower part of a leg. This wire passes over three pulleys and is connected to a ten kg weight. The tension in the wire is shown near the leg in the direction of the wire. On the leg, a point on knee is shown as the pivot. The distance between the pivot and the point where the wire is tied to the leg is thirty five centimeters. A free-body diagram of the leg, represented as a pole, is shown.
A mass is connected by pulleys and wires to the ankle in this exercise device.
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A person working at a drafting board may hold her head as shown in [link] , requiring muscle action to support the head. The three major acting forces are shown. Calculate the direction and magnitude of the force supplied by the upper vertebrae F V size 12{F rSub { size 8{V} } } {} to hold the head stationary, assuming that this force acts along a line through the center of mass as do the weight and muscle force.

The head of a person working at a drafting board in relaxed position is shown. The inclination of the head is theta to the horizontal and the center of gravity is near the top of the head. The weight of the head is fifty newtons and is acting downward at the center of gravity. Three major forces are shown. The force exerted along the neck is sixty newtons.

F V = 97 N, θ = 59º size 12{F rSub { size 8{V} } ="97"`N,`θ="59"°} {}

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Questions & Answers

differentiate between demand and supply giving examples
Lambiv Reply
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Lambiv
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appreciation
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In economics, a perfect market refers to a theoretical construct where all participants have perfect information, goods are homogenous, there are no barriers to entry or exit, and prices are determined solely by supply and demand. It's an idealized model used for analysis,
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What is ceteris paribus?
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other things being equal
AI-Robot
When MP₁ becomes negative, TP start to decline. Extuples Suppose that the short-run production function of certain cut-flower firm is given by: Q=4KL-0.6K2 - 0.112 • Where is quantity of cut flower produced, I is labour input and K is fixed capital input (K-5). Determine the average product of lab
Kelo
Extuples Suppose that the short-run production function of certain cut-flower firm is given by: Q=4KL-0.6K2 - 0.112 • Where is quantity of cut flower produced, I is labour input and K is fixed capital input (K-5). Determine the average product of labour (APL) and marginal product of labour (MPL)
Kelo
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what is monopoly mean?
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What is different between quantity demand and demand?
Shukri Reply
Quantity demanded refers to the specific amount of a good or service that consumers are willing and able to purchase at a give price and within a specific time period. Demand, on the other hand, is a broader concept that encompasses the entire relationship between price and quantity demanded
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Economic growth as an increase in the production and consumption of goods and services within an economy.but Economic development as a broader concept that encompasses not only economic growth but also social & human well being.
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Jabir
What do you think is more important to focus on when considering inequality ?
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Asui
it is a curve that we get after connecting the pareto optimal combinations of two consumers after their mutually beneficial trade offs
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In economics, the contract curve refers to the set of points in an Edgeworth box diagram where both parties involved in a trade cannot be made better off without making one of them worse off. It represents the Pareto efficient allocations of goods between two individuals or entities, where neither p
Cornelius
In economics, the contract curve refers to the set of points in an Edgeworth box diagram where both parties involved in a trade cannot be made better off without making one of them worse off. It represents the Pareto efficient allocations of goods between two individuals or entities,
Cornelius
Suppose a consumer consuming two commodities X and Y has The following utility function u=X0.4 Y0.6. If the price of the X and Y are 2 and 3 respectively and income Constraint is birr 50. A,Calculate quantities of x and y which maximize utility. B,Calculate value of Lagrange multiplier. C,Calculate quantities of X and Y consumed with a given price. D,alculate optimum level of output .
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Answer
Feyisa
c
Jabir
the market for lemon has 10 potential consumers, each having an individual demand curve p=101-10Qi, where p is price in dollar's per cup and Qi is the number of cups demanded per week by the i th consumer.Find the market demand curve using algebra. Draw an individual demand curve and the market dema
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suppose the production function is given by ( L, K)=L¼K¾.assuming capital is fixed find APL and MPL. consider the following short run production function:Q=6L²-0.4L³ a) find the value of L that maximizes output b)find the value of L that maximizes marginal product
Abdureman
types of unemployment
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What is the difference between perfect competition and monopolistic competition?
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Source:  OpenStax, College physics. OpenStax CNX. Jul 27, 2015 Download for free at http://legacy.cnx.org/content/col11406/1.9
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