GGR320H1 Midterm: Midterm study notes

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aquamarinecheetah513

18 Dec 2011

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1. -the generalization of maket relations and the development of modern forms of production have historically had a disruptive effect on traditional work structures. Mobalizes new sectors of population into regional and long-distance migrations. Due to the high degree of concentration of direct foreign employment. Disruption of traditional work structures ex commercial agri. These migrations have contributed to the disruption of tradition, often unwaged, employment structures. Large mobilization of young women into waged labour. Feminization of the new preoletariat contributed to male unemployment and male emigration. None of this would happen if not for large scole investment in manufacturing and agri. Developing countries could not have penetrated the export market in the absence of these things. Workers using their labour power in the production of goods and services demanded by the people and firms of the us. Immigration can be seen as providing labour for one: low wage, service jobs (ex.

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Astrophysicists in the 1960s tried to explain the existence and thestructure of pulsars â extremely regular astronomical sources ofradio pulses whose periods ranged from seconds to milliseconds. Atone point, these radio sources were given the acronym LGM, standingfor âLittle Green Men,â a reference to the idea that they might besignals of extraterrestrial civilizations. The explanation giventoday is no less interesting. Consider the following. Our Sun,which is a fairly typical star, has a mass of 1.99x10^30 kg and aradius of 6.69x10^8 m. Although it does not rotate uniformly,because it isnât a solid body, its average rate of rotation isabout 1 rev / 25 days. Stars larger than the sun can end theirlives in spectacular explosions called supernovae, leaving behindcollapsed remnants of the stars called neutron stars. Neutron starshave masses comparable to the original masses of the stars, butradii of only a few kilometers. These stars emit beams of radiowaves. Because of the rapid angular speed of the stars, the beamssweep past Earth at regular, very short, intervals. To produce theobserved radio-wave pulses, the star has to rotate at rates fromabout 1 rev/s to 1000 rev/s.

a. Estimate the rotation rate of the Sun if it were to collapseinto a neutron star of radius 10 km. The Sun is not a uniformsphere of gas, and its moment of inertia is given by I = 0.059MR2.Assume that the neutron star is spherical and has a uniform massdistribution.
b. Is the rotational kinetic energy of our Sun greater of smallerafter the collapse? By what factor does it change, and where doesthe energy go to or come from?

Hi this is the introduction that I have written for my poster. Myposter is on the following URL (please have a look!).

http://i55.tinypic.com/e0g0w5.jpg

Please correct the introduction for any scientific or grammaticalerrors and give me your suggestions about this section as well asthe overall poster. Thanks

This is very important so if you are not good at it pleasedon't answer.

Here is the introduction :

Have you ever thought about why would thrilling rides getyou excited, make your heart racing orsometimes even make you start screaming from the depths of yourcore, forming a bead of sweat on your forehead?

Well, the answer lies in physics. These rides demonstratevery good examples of the physics laws and concepts involved innature and their affect on us in real life applications.

Height, weightlessness, high velocity, hugeacceleration, the sudden impulse and themomentary change in momentum, the work being done and the suddenchange in energy are all factors that contribute inmaking a thrilling ride an exciting one. Those factorsmake adrenalin concentrations in our body system increasecausing higher blood pressure thus stimulating theheart.. They also make the rider in a lot ofuncertainty and unexpected visual cues.

An example of a thrilling ride is the Giant Drop which isa freefall ride involving the drawing of an eight seat carriage bytwin cables to the top of the tower. After one minute full ofanxiety, the riders are plummeted down a height of 39 stories(almost 115m) then brought to a halt within meters from the groundby a sophisticated magnetic braking system.

Materials fracture when the force per unit area, called STRESS,exceeds a critical value. In general, the critical stress dependson the direction as well as the magnitude of the force. Forexample, bones break differently when subjected to torsional(twisting) stress than when subjected to compressional (orsqueezing) stress. Let us consider compressional stress. Wet humanbone for 20-39 year olds has an ultimate compressive strength of ~16x104Ncm2 [8]. Consider a person who falls from a height to theground. Upon landing, the person's kinetic energy is converted towork. If the person decelerates over a distance h, we can estimatethe average force during the collision by

If a person lands stiff-legged on a hard surface and doesn'tbounce, the deceleration occurs over a very short distance, h ~ 1cm. Since the force is transmitted up the leg, the stress isgreatest where the cross-sectional area is least, i.e., the tibiajust above the ankle [8].
The following lists some different conditions that may occur duringlanding and physical explanations for why they make bone fracturefrom a fall more or less likely [8]:

(a) bounce [more likely. The impulse is twice as large for anelastic collision as for an inelastic collision.]
(b) bent knees [less likely. Bending the knees increases the timeand distance over which deceleration occurs, which reduces theforce.]
(c) landing in loose earth or sand [less likely. This increases hwhich reduces F.]
(d) turning the body to land on the side [less likely. Thisincreases h. It also distributes the force widely over the body(increases A), thereby reducing the stress.]

So, why can a properly executed karate kick break a concrete blockwithout fracturing bones [16]? First, bone is a very strongmaterial. Its ultimate compressive strength is approximately 40times larger than concrete. Second, contact is made with the edgeof the foot. This concentrates the force into a small area of thetarget and reduces the likelihood of bending a bone to the point offracture. Third, the collision with the target is essentiallyinelastic and extends over several milliseconds, so the peak force,though large, does not exceed the strength of the bone. If A(cross-sectional area of the tibia) ~ 3.3 cm2, compute how far a 69kg person can fall and land stiff-legged on both legs withoutbreaking a bone. Assume F is split evenly between two legs. (Hint:F<or =2(theta)A )

GGR320H1 Midterm: Midterm study notes

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