# Physics Essay

Physics Assessment Task Tony Wang 1 . Assess the reasons for the introduction of low speed zones in built-up areas and the addition of air bags and crumple zones to vehicles with respect to the concepts of impulse and momentum: Air Bags and Crumple Zones both increase the stopping distance of a vehicle. Relating to Impulse = Force times Distance, If the distance is increased, the force is lower, this reduces the forces put on an the vehicle, and the occupants inside it.

Low Speed zones are in place because, the slower your velocity, the less momentum you have and the faster you can stop. . Identify data sources, gather, process, analyses, present secondary information and use the available evidence to assess benefits of technologies for avoiding or reducing the effect of a collision Includes, Air Bags, Crumple Zones and Seat Belts. 1 . The Use of the Airbag I The purpose of an airbag is to help the passenger in the car reduce their speed in collision without getting injured. Objects in a car have mass, speed and direction.

If the object, such as a person, is not secured in the car they will continue moving in the same direction (forward) with the same speed (the speed the car was going) hen the car abruptly stops until a force acts on them. Every object has momentum. Momentum is the product of a passenger’s mass and velocity( speed with a direction). Len order to stop the passenger’s momentum they have to be acted on by a force. In some situations the passenger hits into the dashboard or windshield which acts as a force stopping them but injuring them at the same time. An airbag provides a force over time.

This is known as impulse. The more time the force has to act on the passenger to slow them down, the less damage caused to the passenger. There is a restricted amount of time that the airbag has to act between when the car hits the other object and the passenger hits the steering wheel. About 15 to 20 milliseconds after the collision occurs the crash sensors decide whether or not the collision is serious enough to inflate the airbag (usually 6 – 10 km/h). If the crash sensors decide to inflate the airbag it will be deflated at about milliseconds after the crash.

It takes about 20 milliseconds to inflate the airbag for the person to land into. Around 60 milliseconds the person has made contact with the airbag and the airbag now starts to deflate. The passenger continues to be acted on by the airbag as it is in the deflation process which takes about 35 to 40 milliseconds. It is still necessary to wear a seat belt although all auto-mobiles must be equipped with an airbag because of a few reasons: 1) The crash sensors do not signal for the airbag to inflate unless the vehicle is moving at least 6 km/h. Damage can still occur to the passenger if the collision is of a slower speed.

This is were the seat belt plays an important role. 2) The airbag located in the steering wheel does not help the passenger in a collision where another car hits them side on. ) When the car the passenger is in is backing up and collides the its rear end with another object the airbag does not help. With today’s technology other airbags are being introduced in are being introduced are side airbags and head airbags. 2. The Use of the Crumple Zones on cars Auto safety has come a long way in the last few decades, and one of the most effective innovations is the crumple zone.

Also known as a crush zone, crumple zones are areas of a vehicle that are designed to deform and crumple in a collision. This absorbs some of the energy of the impact, preventing it from being reanimated to the occupants. Of course, keeping people safe in auto accidents isn’t as simple as making the whole vehicle crumple. Engineers have to consider many factors in designing safer cars, including vehicle size and weight, frame stiffness and the stresses the car is likely to be subjected to in a crash.

For example, race cars experience far more severe impacts than street cars, and Subs often crash with more force than small cars. 3. The importance of stables PURPOSE: The Job of the settable is to hold the passenger in place so the passenger is almost part of the car which prevents the passenger from flying forward as the car stops abruptly in the case off collision. Real Life Situation When a car stops suddenly due too collision with another object such as another car, a tree, pole, guardrail, etc. The car’s acceleration decreases very quickly in a short period of time.

This is called deceleration. Newton’s Law of Inertia explains how this happens. LAW OF INERTIA: An object in motion continues in motion with the same speed and direction unless acted upon by an unbalanced force. As the car collides with another object, the other object provides the force which changes the speed and direction. The car stops going in the direction it was going in, and in some cases bounces back depending how hard of a force hits it or how much momentum the car had. Also, the speed decelerates quickly due to the impact.

When all this happens the passenger is not being acted upon by a force to slow them down. This part is where the settable comes into play. As the person continues in their same direction and speed ( forward and the same speed that the car was going) the settable catches them, holding them back from flying through the air. The alternative is to not wear a settable, but a force will still eave to act on the person in order to slow them down. This force will come from the dashboard or windshield as the person crashes into it causing a lot of damage to themselves. A settable has two parts.

The first part rests over the passengers pelvis and the second part rests over the shoulder and across the chest. When the car stops abruptly the settable applies the stopping force across a large section of the body so the damage is reduced. Stables are made of flexible materials which have more give then a dashboard or windshield would have. Since stables are flexible one might ask how do they hold you in place? Stables are designed so that the machinery behind them tightens up the belt to hold the passenger in place when the car decelerates quickly. . Describe a Heartstrings-Russell diagram as the graph of a star’s luminosity against its color or surface temperature The HER diagram is one of the most important tools in the study of stellar evolution. Developed independently in the early asses by Jejuna Heartstrings and Henry Norris Russell, it plots the temperature of stars against their luminosity ethical HER diagram), or the color of stars (or spectral type) against their absolute magnitude (the observational HER diagram, also known as a color-magnitude diagram).

Depending on its initial mass, every star goes through specific evolutionary stages dictated by its internal in the temperature and luminosity of the star, which can be seen to move to different regions on the HER diagram as it evolves. This reveals the true power of the HER diagram – astronomers can know a star’s internal structure and evolutionary stage simply by determining its position in the diagram. I What is luminosity? When you look at the night sky, you can see that some stars are brighter than others as shown in this image of Orion.

Two factors determine the brightness of a star: animosity – how much energy it puts out in a given time distance – how far it is from us A searchlight puts out more light than a penlight. That is, the searchlight is more luminous. If that searchlight is 5 miles away from you, however, it will not be as bright because light intensity decreases with distance squared. A searchlight 5 miles from you may look as bright as a penlight 6 inches away from you. The same is true for stars.

Astronomers (professional or amateur) can measure a star’s brightness (the amount of light it puts out) by using a photometer or a charged couple device (CDC) on the end of a telescope. If they know the star’s brightness and the distance to the star, they can calculate the star’s luminosity [luminosity = brightness x 12. 57 x (distance)2]. Stefan-Balletomane Law This is the relationship between luminosity (L), radius (R) and temperature (T): L = (7. 125 x 10-7) RE TO Units: L- watts, R- meters, T- degrees Kelvin I Luminosity is also related too star’s size.

The larger a star is, the more energy it puts out and the more luminous it is. You can see this on the charcoal grill, too. Three glowing red charcoal briquettes put out more energy than one glowing red charcoal briquette at the same temperature. Likewise, if two stars are the same temperature but different sizes, then the large star will be more luminous than the small one. See the sidebar for a formula to that shows how a star’s luminosity is related to its size (radius) and its temperature. 4. Identify energy sources characteristic of each star group, including Main Sequence, red giants, and white dwarfs One of the most useful and powerful plots in astrophysics is the Heartstrings-Russell diagram (hereafter called the H-R diagram). It originated in 1911 when the Danish astronomer, Jejuna Heartstrings, plotted the absolute magnitude of stars against their lour (hence effective temperature). Independently in 1913 the American astronomer Henry Norris Russell used spectral class against absolute magnitude.

Their resultant plots showed that the relationship between temperature and luminosity of a star was not random but instead appeared to fall into distinct groups. These are seen in the H-R diagram above. It has a few specific stars included in the plot but otherwise Just shows the main regions. 1 . What is a Main Sequence Star? Main sequence stars are around us, our sun is a sun like star. Main sequence stars are usually medium sized stars. Through out this page, we will use our Sun as an time. The sun is 865,400 miles (1 kilometers) in diameter.

The sun has a mass 332,000 times that of the Earth. It makes up 99. 8% of our Solar System’s mass! The temperature is very hot, at about 10 to 20 million degrees Celsius (3600032. 36 degrees Fahrenheit and) The sun is a star type G. Like most other stars, sun- like stars take part in nuclear fusion. This is a process of turning the element Hydrogen into Helium. A Main Sequence Star’s Life Cycle A main sequence star begins as a nebula, but after that, there can be two ways that a main sequence star can form. The first way is when the nebula collapses and turns into a Protestor.

As the core of the Protestor reaches 10 million degrees, it creates nuclear energy. This energy will provide for 90% of the sun-like star’s life! As this energy is formed, pressure builds up inside the Protestor. This pressure creates photons. This causes gravity inside the main sequence (this gravity currently allows the planets of our Solar System to orbit around the sun). Finally the production of photons ends, and it is the beginning of the sun-like stars life. This is referred to by astrophysicists as “Zero Age”. The second way, comes after the nebula has collapsed.

After the collapse, a globule is formed. It slowly moves and rotates. As gas pressure builds up and the globule collapses. It cools and the spinning, size, and temperature increase. This creates a proprietary disk and core. The proprietary disk could become a planet, while the core will become the main sequence. During the stars life, it will produce nuclear fusion in the core of the star. As this star begins to fade, the production of nuclear fusion from fading hydrogen nuclei will slow, at the same time, photons will also stop producing.

The gravitational force will decrease rapidly as the outward pressure (photons) and the inward pressure (hydrogen nuclei) slow. This will cause all the helium nuclei to collapse again. Hydrogen will surround the collapsed star. There will be a greater outward pressure than inward pressure. This will cause the star to expand, get brighter, and get hotter. At this point, a red giant has been formed. 2. What is the Red Giant? The Red Giants produce a large amount of light because of their great size. All normal stars are expected to pass through the Red Giant phase at some time in their lifetime.

The Red Giant is usually 10-1500 times the size of our sun’s current size. Most Red Giants are red but some of them are orange or even yellow, because of the amount of different chemicals and or elements inside it. Nuclear Fusion When the hydrogen atoms in a star fuse together, the amount of hydrogen begins to reduce as the amount of helium increases. Since the helium atoms are heavier than the hydrogen atoms, they sink to the center of the core. This goes on for a long time, as hydrogen burns in a shell around the helium in the center.

The quantity of energy produced by the giant decreases quickly over the time that it works. A Red Supernatant Soon the outer edges expand and loose heat even faster and the star appears as a red giant. When the star reaches the size nearly 1. 4 times the size of out sun, it is As the outer edges continue to expand, the core shrinks and heats up. When the temperature in the core hits KICK, helium atoms fuse together, forming carbon. Carbon does not compress as much as the helium so the core is now stabilized. Then, at the end off red giant’s life, it explodes in a supernova. . What is a White Dwarf Star? A white dwarf is the final stage of the evolution of a star that is between . 07 and 1. 4 solar masses. White dwarfs are supported by electron degeneracy. They are found to the lower left of the main sequence of the Hearthrugs Russell diagram. White dwarf stars got their name because the first to be discovered had a white color. They are characterized by a low luminosity, a mass close to that of our sun, and a radius only that of the earth. These stars are extremely dense because their large mass and small area.

Their density is almost 1,000,000 time that of water. White dwarfs also have a low luminosity. This makes it so they have to be within a few hundred parsecs away from earth to be observed (1 parsec = 3. 26 light years). Facts About White Dwarfs! When a star stops burning the stars with less than 1. 4 solar masses shrink greatly in size. While they shrink they start to become very faint. The value of 1. 4 solar masses is referred to as the Chandeliers limit. Chandeliers reasoned that something must be holding up the White Dwarfs material against gravity.

This was known as the electron degeneracy. When stars contract the electrons get close together there resistance keeps increasing and pushing closer together. This process is related to pressure. At great densities, pressure from the degenerate electrons is sufficiently sigh. It balances the force of gravity and the star stops contracting. So electron degeneracy stops the white dwarf form contracting and compresses the gas of the star. This means that the White Dwarf becomes incredibly dense. A mass the size of the sun is compressed into a volume only the size of the earth.

What is the Chandeliers Limit? The Chandeliers limit is the maximum possible mass for a stable White Dwarf star. The name was given after the Indian-born astrophysicist Subterranean Chandeliers, who formulated it in 1930. Using Einstein special theory of relativity and the reminisces of quantum physics, Chandeliers showed that it is impossible for a white dwarf star, to be stable if its mass is greater than 1. 4 times the mass of the Sun. EXAMPLE: all direct mass determinations of actual white dwarf stars have resulted in masses slightly less than the Chandeliers limit.

A star that ends its nuclear-burning lifetime with a mass greater than the Chandeliers limit must form into either a neutron star or a black hole. What Happens in Time? Pressure from degenerate electrons doesn’t depend on temperature so stars are stable even though no more energy is ever generated within them. Because of electron degeneracy they are unable to contract any further. However, they still have stored energy that will radiate for a few billion years. Once the star burns out in the cycle. It now becomes a cold and inert stellar remnant sometimes called a black dwarf.

Our Sun is destined to die as a white dwarf. Before the sun transforms into a white dwarf it will turn into a red giant. When the sun becomes a red giant it will engulf Mercury and Venus in the process and at the same time it will blow away the earth’s atmosphere and boil the oceans. This will make earth uninhabitable. However this process will take billions of years to develop. In conclusion: HER Group Energy Sources Main Sequence Nuclear Fusion of Hydrogen to Helium in core. Red Giants Nuclear Fusion of Helium to Carbon in core, with Hydrogen fusion continuing in shell.

White Dwarfs No nuclear fusion 5. Process and analyses information using the Heartstrings-Russell diagram to examine the variety of star groups, including Main Sequence, red giants, and white dwarfism’s Sequence on the Heartstrings-Russell Diagram This Heartstrings-Russell diagram shows a group of stars in various stages of their evolution. By far the most prominent feature is the main sequence, which runs from he upper left (hot, luminous stars) to the bottom right (cool, faint stars) of the diagram. The giant branch is also well populated and there are many white dwarfs.

Also plotted are the Morgan-Keenan luminosity classes that distinguish between stars of the same temperature but different luminosity. –>There are 3 main regions (or evolutionary stages) of the HER diagram: The main sequence stretching from the upper left (hot, luminous stars) to the bottom right (cool, faint stars) dominates the HER diagram. It is here that stars spend about 90% of their lives burning hydrogen into helium in their cores. Red giant and supernatant stars luminosity classes I through Ill) occupy the region above the main sequence.

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