Gabriel


 * __"It's all relative" sheet:__**

1- 28-10=18 -> 18 = 360/t -> t = 360/18 -> t = **20s**

2- **Velocity = Distance/time**
 * __"Relative motion" sheet:__**

1- As the trucks are coming aganist each other, the module of the velocities are added to each other as well. Then we have that 100 km/h + 60 km/h = 160 km/h, So the speed of "C" relative to "D" is **160 km/h.**

2- a)For the same reason as explained above, the velocity of "X" relative to "Y" is **55.56 m/s**, since both are at the same velocity of 27.78 m/s and 27.78x2= 55.56.

b) Each one second each car gets 27.78 meters closer, so if both have the velocityof 27.78 m/s(relative to the ground) and are travelling at the same direction, **they will get 55.56 meters closer for each second that passes.**

3- For the same reason as explained at the first question of this sheet, **the relative velocity of the second car to the first is 5.5 m/s**, since the first one is at a velocity of 30.5 m/s and the second at 25 m/s and 30.5 - 25 = 5.5.

4- Since the fielder and the ball are moving aganist each other, their velocities are added, so we have that: 12m/s+5m/s=17m/s, so **the relative velocity of the fielder to the ball is 17m/s** 5- To know if it is safe to overtake, you must discover if you can go back to your saide of the road before the other car passes you. So if you will take 10 seconds to finish your overtake and the other car is 500m far from you, we must discover how far each car can go in 10 seconds. Then

Car "A"(you): Velocity=90 km/h(25 m/s) -> 25= dist/10 -> dist = 250m

Car "B": Velocity= 100 kh/h (~27.7 m/s) -> 27.7=dist/10 -> dist = 277m

So when you finish your overtake, you will be at the "mark 250m"(from your point of view) and the other car will be at the "mark 228m", or it be he would had passed trough you, or better: you would be involved at a car crash. **Then the conclusion is:Its unsafe to overtake, if you try you will probably crash,or at least have to evade the other car.**

__**Biography:**__
Isaac Newton (25/10/1642 - 20/01/1727) was an English Physicist,Mathematician, Astronomer, and alchemist, who was considered by many to be the" greatest and most influential Scientist who ever lived." Newton was born 3 months after his father's(also named Isaac Newton) death, he had a troubled childhood, where his mother married again with a step father that the disliked and tried to make of him a farmer. When Henry Stokes(master at the "king's school" convinced her mother to send him back, he became the top-ranked student(part motivated by revenge against a bully). At his middle years, he made remarkable discoveries/theories, such as the three laws of motion and the gravitational theory.  At the end of his life he wrote religious tracts, became a member of the parliament of England. But he moved to London to pick up a post of warden of the royal mint, a position that he had obtained through the patronage of Charles Montagu Finally Newton took up residence at Cranbury park,nearWinchester with his niece and her husband, until his death in 1727. Newton died in his sleep in London on 31/03/1727. After his death, Newton's body was discovered to have had massive amounts of Mercury in it, probably resulting from his alchemical pursuits.


 * __Contribution to__** **__physics__** **__and motion:__**

In this work, Newton described universal gravitation and three laws of motion, which dominated the scientific view of the physical universe, for the next three centuries. Newton showed that the motions of objects on earth and of celestial bodies are governed by the same laws, by demonstrating the consistency between Kepler's laws of planetary motion and his theory of gravitation, removing the last doubts about heliocentrism and advancing the scientific revolution.


 * __Laws of motion:__**


 * Newton's First Law** (also known as the Law of inertia) states that an object at rest tends to stay at rest and that an object in uniform motion tends to stay in uniform motion unless acted upon by a net external force.

Ex: Anything at a vacuum (if not touching any surface) shall continue its trajectory forever, without any change.


 * Newton's Second Law** states that an applied force,"F", on an object equals the rate of change of its momentum,"P", with time. Mathematically, this is expressed as



If applied to an object with constant mass (d.//m///d//t// = 0), the first term vanishes, and by substitution using the definition of acceleration, the equation can be written in the iconic form:


 * __Where:__** F=force/ M= mass/A= acceleration.


 * Newton's third law** states that every action will have a reaction with the same module and direction but in a different way.


 * __Others laws:__**


 * Newton's law of universal gravitation** states that Every __point of mass__ attracts every single other point mass by a __force__ pointing along the __line__ intersecting both points. The force is the proportional product of the two __masses__ and __inversely proportional__ to the __square__ of the distance between them. The formula is:

, **__Where:__** F= force/G= gravitational constant/M1=First mass/M2=Second mass/ r = Distance between the **centers** of the masses. = = =__**Importance of the gravity law:**__=

Newton’s Law of Universal Gravitation grew in importance as scientists realized its utility in predicting the orbits of the planets and other bodies in space. Note that Einstein proved that this law fails when the gravity is extremely strong.

=__Notes about the video:__= - Every object on earth is under the influence of the "normal",that is a force that the ground exerts at the object depending on its weight, the formula is: **N= M.G**(Where
 * N**= normal/**M**=mass/**G**= acceleration of the gravity). Normal has an angles of 90 degrees.

-Every surface(even the air) creates friction( **Fat= M.N**, Where **Fat**= Friction force/**M**= friction coefficient/**N**= normal), friction slows down any object in motion.

-Every moving object will continue its movement without any change nor in direction,nor in module and nor in its way unless unbalanced forces act on it.

-Every stationary object will remain at rest unless unbalanced forces act on it(this property is called inertia)

-**Fnet=W-N=0** (**Fnet**= net force/**W**=weight/**N**= normal)

==== To protect the back of the egg i used cottom wool,that is a soft material and collapses when under pressure,therefor reducing the momentum of the egg, in front of the egg there was an elastic band to avoid deaccelerate it when the car stops,so it wouldn`t fly over the trolley.The cottom wool was tied by a strip of fabric. ====

__** Social effects of crashes: **__
==== Being involved in a car crash is painful and traumatizing alone,but after this you still have to pay for the injuries. Beyond that,even if you are not involved you may pay a high price. Car crashes don´t just crash the cars but the road and surrondings as well, what means that the governament will have to spend money to reconstruct them and change traffic ways to do so. Therefor many people may get late/lose their appointments by others irresponsability(or bad road conditions that may have caused the accident) ====

And car crashes are always bad events that generally took peoples life,which may interfer at a comunity activities.

 * __How does a GPS works:__**

For the initial position calculation your GPS chipset needs to find at least 4 satellites with a strong enough signal (28 dBHz or more) and it must keep those satellites and the signal strength for approximately one minute in order that it can download the data from the satellites that is essential for calculating your position. If at any time the GPS receiver loses the signal of any satellite or the signal drops below 28 dBHz then it has to start all over again and track that satellite for another minute. In a real life scenario for example, you may be driving between high buildings and the received GPS signal keeps changing all the time. The QuickFix file you can download from the internet is part of a solution from your GPS chip manufacturer. SiRF call their solution Instant Fix (I Edition) or A-GPS (assisted GPS). The file contains specially prepared __ephemeris data*__ that is valid for 7 days that your GPS chip uses instead of the the data received from satellites for calculating your first fix. This allows the chip to skip the "download ephemeris from satellite" step and instead to start calculating your position immediately after powering on. This takes around 5-15 seconds on average. The signal strength required for downloading ephemeris data from satellites is 28dbHZ whereas the signal strength required for calculating your position once your GPS has received the ephemeris data is much lower at only 15 dBHz. So a valid QuickFix file allows your device to calculate your position in 5-15 sec rather than the minute it would otherwise take (if stationary), and lowers the minimal signal strength required for calculating your position from 28 dBHz to 15 dBHz.

__**Here is an image of how the satellites try to calculate your position:**__
 * __* Ephemeris data__** = is data that tells the GPS receiver where each GPS satellite should be at any time throughout the day. Each satellite will broadcast its OWN ephemeris data showing the orbital information for that satellite only. Because ephemeris data is very precise orbital and clock correction data necessary for precise positioning, its validity is much shorter. It is broadcast in three six second blocks repeated every 30 seconds. The data is considered valid for up to 4 hours but different manufacturers consider it valid for different periods with some treating it as stale after only 2 hours.