Ch5_ShermanB

CHAPTER 5 toc

= Lesson 1, Motion Characteristics For Circular Motion, Method 5 =


 * 1) Speed and Velocity
 * 2) //Heading: Same speed, different direction!//
 * 3) Article: An object in circular motion can travel the perimeter of a circle, or it’s circumference, in a constant amount of time. Objects traveling in circular motion have a constant speed but changing velocity, and their velocity is called a tangential velocity vector. This means the direction of a velocity vector is always changing, and the direction of the velocity vector at any point is found by drawing a tangent line on the circle.
 * 4) Acceleration
 * 5) //Heading: Changing direction = acceleration!//
 * 6) Article: The process of subtracting vectors Vi and Vf on a circle results in a change in velocity. The acceleration of is dependent on the velocity change, and is in the same direction as the change in velocity.
 * 7) The Centripetal Force Requirement
 * 8) //Heading: Make sure to satisfy the centripetal force requirement!//
 * 9) Article: Objects at motion have a net force, called centripetal force, which acts towards the center of an object, is in the direction of acceleration, and is called the centripetal force requiremen. This relates to Netwon’s first law of inertia because all objects with balances forces travel in a straight line, and centripetal force causes objects in uniform circular motion to continue in the circular path with a push or pull on the object toward the center. Centripetal force isn't a new force, but rather the description of the direction of the net force.
 * 10) The Forbidden F-Word
 * 11) //Heading: Centrifugal forces are a lie!//
 * 12) Article: A centrifugal net force doesn’t exist. That is because if it did, there would have to be an outward force, which doesn’t exist. There is no object in existence that pushes or pulls a person outwards, and if it did, you wouldn’t continue traveling in circular motion.
 * 13) The Mathematics of Circular Motion
 * 14) //Heading: Got an equation? Use em' for circular motion!//
 * 15) Article: The equations for speed, acceleration, and force can be used to guide problem solving, as well as guide a person into thinking the impact of changes. Through these equations many relations can be found. For example, there is a relationship between acceleration and net force, acceleration and mass, net force and speed, and others.

= Lesson 2, Applications of Circular Motion, Method 4 =


 * 1) Newton's Second Law - Revisited
 * 2) How can Newton's second law be applied to circular motion questions?
 * 3) Newton's laws fit perfectly with circular motion, since F=ma on an object in circular motion.
 * 4) How do we illustrate an object being acted upon in circular motion?
 * 5) A free body diagram is used to show the forces acting on an object, even if it's in circular motion.
 * 6) How do we satisfy the centripetal force requirement on an FBD?
 * 7) We know that net force acting upon an object is acting inward, so this should be remembered and used to help draw the FBD.
 * 8) Amusement Park Physics
 * 9) Why do people ride on roller coasters?
 * 10) Roller coasters cause the rider to experience thrilling or frightening changes in acceleration.
 * 11) What types of sections exist on a roller coaster track?
 * 12) Roller coasters have sharp 180 degree banked turns, small dips and hills, and clothoid loops.
 * 13) What is a clothoid loop?
 * 14) A clothoid loop is a section of a spiral where the radius is constantly changing. This is unlike a circular loop, where the radius is always the same.
 * 15) The amount of curvature at the bottom of a clothoid loop is much higher than that at the top, which translates into a higher radius at the bottom than at the top.
 * 16) How is a roller coaster rider impacted while riding on a clothoid loop?
 * 17) The rider's direction is constantly changing (acceleration), they are constantly changing speed, and climbing the loop causes a decrease in speed and decrease in kinetic energy, while going downwards causes an increase in speed and kinetic energy.
 * 18) What are the components of an object moving through a noncircular loop at non-constant speed?
 * 19) Component directed at the center of the circle, which relates to direction change.
 * 20) Component on a tangent, relates to change in speed.
 * 21) What is the magnitude of the normal force of gravity acting on a roller coaster passenger?
 * 22) Depends on the speed of the car, the mass of the passenger, and the radius of the loop.
 * 23) Magnitude is always greatest at the bottom
 * 24) Normal force must always be of the appropriate size as to combine with the force of gravity to produce centripetal net force.
 * 25) At the bottom, the magnitude of net force is pointed outwards from the center of the loop.
 * 26) The normal force must be large enough to overcome the force of gravity to supply excess force to result in a net inward force.
 * 27) At the top of the loop, the force of gravity and the net force are pointed downwards.
 * 28) What is the suggested method to solve circular motion problems?
 * 29) Draw a FBD, with all forces represented by a vector arrow and labeled.
 * 30) Identify givens and unknowns
 * 31) If any forces are directed at angles to the horizontal or vertical, use vector principles to resolve the forces into horizontal and vertical components.
 * 32) Determine the magnitude of any known forces, and label on the FBD
 * 33) use circular motion equations to find unknown variables
 * 34) use remaining information to solve for requested information, this can require kinematics equations to be used
 * 35) Why do people feel as if they have different weights on roller coasters?
 * 36) At different points, the normal force acting on the rider will be different than what they usually feel. They will feel weightless at the top of the roller coaster, and heavier at the bottom.
 * 37) Why are clothoid loops used on roller coasters?
 * 38) Cars would move too quickly on curves or loops, causing people to fall out, or be injured to from experiencing too much acceleration.
 * 39) At some points, the normal forces were so strong that they could break bones or cause whiplash.
 * 40) Lower entry speeds and different curvature in the loops fixed problems with injuries or inabilities for the cars to follow through the loop.
 * 41) How are hills and dips related to roller coaster experimentation?
 * 42) At various points along hills and dips, riders are on circular arcs. This arc is part of a circle, and thus the equation a = v^2/r can be used to find their acceleration, and show the effect on the net force.
 * 43) Athletics
 * 44) How are turns an example of circular motion in sports?
 * 45) Some turns are circular, concepts of math and circular motion can be applied.
 * 46) The turning object has inward acceleration, with the direction of acceleration being towards the center of the circle that the turn is on.
 * 47) Something needs to apply inward force to fit the centripetal force requirement.
 * 48) A person turning on a horizontal surface leans into a turn, so the surface pushes up at an angle to the vertical (so there is a horizontal and vertical component).
 * 49) They are contact forces, which has two roles. The first is to balance the downward force of gravity, and the second is to meet the centripetal force requirement of circular motion.
 * 50) What forces act on a turning skater?
 * 51) Force acting between the ice skates and the ice - combo of a normal force and friction force,
 * 52) The normal force is a result of a stable surface and an object pushing down on it, and the friction force is a result of static friction from the skates on the ice.
 * 53) In the turn, the skater pushes down and out on the ice. The blade of the skate makes a groove in the ice, which the blade can push outward on. Netwon's third law says that the groove pushes back on the skater, which results in a grip on the ice.
 * 54) Are there any special equations to use for circular turns in athletics?
 * 55) No, all the previously learned equations can be applied to athletics, as well as the steps for solving a circular motion question. (see the previous reading).

= Lesson 3, Universal Gravitation, Method 2B =


 * 1) Gravity is More than A Name
 * 2) In the reading, I understood the basic definition of gravity. This definition is that gravity is a force that pulls objects toward the Earth, and that all objects on Earth are acted on by the force of gravity. For example, if you jump up, gravity pulls you down faster and slows you down when you're rising. I also understood that acceleration due to gravity (g) is acceleration that all objects that are acted on by gravity are affected by. The value of acceleration due to gravity is 9.8m/s^2 at all places on Earth.
 * 3) I felt that I didn't have any misconceptions in the reading.
 * 4) I felt that I understood everything in the reading.
 * 5) Obviously, gravity can be related to our everyday lives because it's omnipresent on Earth. Wherever we go, we're acted on by gravity, and it is essential in holding us to the Earth.
 * 6) The Apple, the Moon, and the Inverse Square Law
 * 7) From the reading, I learned what an inverse square law is. An inverse square law states that one quantity is equal to the one divided by the square of another quantity. In our case, an inverse square law is used to relate the force of gravity between the Earth and any other object. This law is F grav ~ 1/d 2, where F grav is the force of gravity between two objects (generally the center of the Earth and another object), and that is proportional to one divided by the distance between the two objects squared. From this equation, many relationships can be made, such as that there is an inversely proportional relationship between distance and the force of gravity between two objects. So, as distance increases, the force of gravity decreases. I also learned about Newton's discovery of universal gravitation. Newton realized that if an apple can fall off a tree, then the same force that pulls it down must also pull on the moon, which holds it in Earth's orbit. He concluded that if you launched a cannon ball horizontally off the top of a mountain in the presence of gravity, the ball would fall back to Earth. If you fired the cannon at such a velocity as to have the trajectory match the curvature of the Earth, it would fall around the Earth (orbit). Also, if the velocity was such that the trajectory was greater than that of the curvature of the Earth, the ball would travel in an elliptical path.
 * 8) I felt that the reading was clear.
 * 9) I fully understood everything in the reading.
 * 10) I thought that Newton's idea of gravitational motion was very important, and can relate to real life. I would think that scientists would need to apply the concept of gravitational motion when launching a satellite, so that it orbits the Earth correctly (and can have a planned trajectory).
 * 11) Newton's Law of Gravitational Motion
 * 12) From the reading, I understood Newton's law of universal gravitation. The law, that Fgrav ~ (G*m1*m2/d 2 ) shows the relation between the mass two objects, the distance between them, and the force of gravity that they exhibit on one another. This law is extremely special because it's not just only for finding the force of gravity on Earth, but for the force of gravity between two objects anywhere in the universe. Also from the reading, I understood the relationships between the variables in the law of universal gravitation. For example, more separation between the objects will lower the gravitational force between them, and if the distance is doubled, the force of gravitational attraction will be squared. Another relationship is that gravitational force is directly proportional to the mass of both interacting objects. So, if the mass of either object increases, so does the force of gravitational attraction between them.
 * 13) I felt that the reading was clear.
 * 14) I fully understood everything in the reading.
 * 15) I though that the idea of universality of gravity was interesting, because I had never heard of if before. It is amazing that we can calculate the force of gravitational attraction between two planets using a relatively simple equation.
 * 16) Cavendish and the value of G
 * 17) From the reading, I understood the universal gravitation constant. This constant, G, which has a value of 6.673 x 10 -11 N m 2 /kg 2, is multiplied by m1*m2/d 2 when finding the force of gravity between two objects. This constant is a representation of universal gravity, and is different from "g," which is acceleration due to gravity. The value for G is so small because gravitational attraction only occurs when objects have extremely large masses (like a planet). Also from the reading, I learned how Henry Cavendish was able to measure the universal gravitational constant on something called a torsion balance. In his experiment, he used a light rod about two feet long, with two spheres attached to the end of the rod, which was held up by a thin wire. Cavendish put a smaller sphere next to the larger sphere on the rod, so when the rod became twisted, the torsion that was in the wire exerted a torsional force which was proportional to the angle of rotation of the rod. Since masses attract, the spheres exerted a gravitational force on the smaller spheres and twisted the rod. Once the torsion force was equal to the gravitational force, the rods rested and Cavendish could measure the value.
 * 18) I fully grasped the reading, and had no issue with it.
 * 19) I fully understood everything in the reading.
 * 20) Before reading, I was unsure how the value of G had been calculated in the late 1700's, when there was little technology. This reading clearly showed that even without technology, physicists were able to find values that were a crucial piece to the law of universal gravitation.
 * 21) The Value of g
 * 22) From the reading, I was fully able to understand how acceleration due to gravity is calculated. "g" is calculated with the equation g=(G+M planet )/R planet 2, where G is the universal gravitational constant, Mplanet is the mass of the planet, Rplanet is the radius of the planet, and g is acceleration due to gravity. This equation can be used to find acceleration due to gravity on any planet in the universe. From this equation, we also see that the variation in g with distance follows an inverse square law, which means g is inversely proportional to the distance from the Earth's center. Also from the readiing, I learned why the acceleration due to gravity on Earth is different at different locations. If Rplanet was substituted with the distance from the center of the Earth to the point on the surface where g is being measured, and Mplanet was substituted with the mass of the Earth, we would be able to find g of Earth. If the measurement is taken at a place where the surface is higher or lower than another recorded point, the radius (distance from the center) will change, causing g to increase or decrease.
 * 23) I fully comprehended everything from the reading without issues.
 * 24) I fully understood everything in the reading.
 * 25) Before the reading, I wasn't aware why the value of g changed depending on where it's measured. Although we had said in class that it changed, this reading showed exactly why g has a different value depending on the area where it is measure

= The Clockwork Universe (Method 4) =


 * 1) Part 1
 * 2) What was Copernicus's heliocentric model?
 * 3) the Earth revolved around the sun
 * 4) How did the idea of the heliocentric model cause issues with the Catholic Church later on?
 * 5) church disliked the heliocentric model because it showed that the Earth wasn't at the center of the universe
 * 6) Galileo was tortured for supporting Copernicus's ideas, was forced to renounce his beliefs
 * 7) What was Kepler's modified version of the heliocentric model?
 * 8) planets moved around the sun, but in elliptical orbits instead of circular
 * 9) purely observational
 * 10) Part 2
 * 11) How were Kepler's ideas strengthened by new discoveries in mathematics?
 * 12) René Descartes realized that geometric problems can be recast as algebraic problems
 * 13) Came up with the coordinate plane, so on a large grid, points of an object could be placed according to their X and Y coordinates
 * 14) Also found that lines can have equations that define them
 * 15) What is coordinate geometry?
 * 16) a form of math which represents geometric shapes by equations, and allows truths to be created based on these equations
 * 17) some things were hard to show with traditional geometry, but easy to show using algebra, so this form of mapping combined the two
 * 18) Part 3
 * 19) Why was it good for Newton to be active in physics when Kepler's ideas were unexplained?
 * 20) No physics were strong enough to back Kepler's ideas
 * 21) new form of astronomy called for a new form of physics, which Newton could create
 * 22) What was going on with some forms of science before Newton?
 * 23) people were trying to view the world in a scientific perspective, wanted to know why things happened why they did
 * 24) information was compiled, but not organized correctly or linked
 * 25) Newton provided a way to link all this knowledge
 * 26) didn't have all the answers, but made a framework to find them
 * 27) scientists began to understand the fundamentals
 * 28) future advancements were merely added to Newton's vision
 * 29) What were three important points that described Newton's view that all motion can be explained in a single set of laws?
 * 30) Newton didn't concentrate on motion as much as he did the deviation from steady motion
 * 31) occurs when objects change motion
 * 32) When deviation occurred, Newton looked for a cause


 * 1) Provided a link between force and steady motion quantified the force by proposing his law of universal gravitation
 * 2) Part 4
 * 3) How did Newton follow through with his ideas?
 * 4) Proposed a law of gravity that worked anywhere in the universe
 * 5) used his law and the laws of motion to demonstrate that a single planet would rotate around the Sun in an elliptical orbit
 * 6) concluded that gravity was the cause for this motion, which allowed him to use Newtonian Physics, which he obviously created, to predict gravitational attractions between the planets
 * 7) these attractions would cause small departures from the purely elliptical motion that Kepler described
 * 8) How did Newton's successors use his newly found knowledge?
 * 9) Pierre Simon Laplace (French, 1749-1827) used Newton's discoveries as the basis for a study of mechanics
 * 10) What is determinism?
 * 11) that the universe could be deconstructed using mathematics
 * 12) once a framework was set, the development was predictable
 * 13) How did the Newtonian universe tie in with religion?
 * 14) determinism gave people the idea that the future was ordained, and that all actions were previously defined in the past
 * 15) some felt that this was an indication of God, others felt that it meant that people themselves had free will

=Lesson 4 (A-C), Method 4= >>> period, speed, and acceleration don't call for it, are dependent on the radius of the orbit and the mass of the central body that the satellite is orbiting
 * 1) Kepler's Three Laws
 * 2) What were Kepler's Three Laws?
 * 3) Law of Ellipses - The path of the planets about the Sun is elliptical in shape, with the center of the sun being located at one focus.
 * 4) Law of Equal Areas - An imaginary line drawn from the center of the Sun to the center of the planet will sweep out equal areas in equal intervals of time.
 * 5) Law of Harmonies - The ration of the squares of the periods of any two planets is equal to the ratio of the cubes of their average distances from the sun.
 * 6) What are the details of the Law of ellipses?
 * 7) The closer the foci are to one another, the more closely the ellipse resembles a circle.
 * 8) What are the details of the Law of equal areas?
 * 9) describes the speed at which any given planet will move while orbiting the sun
 * 10) a planet moves its fastest when it's closest to the Sun, and slowest when it's furthest from the Sun
 * 11) if an imaginary line were drawn from the center of the planet to the center of the Sun, the line would sweep out the same area in equal periods of time
 * 12) The areas formed when the Earth is closest to the Sun can be approximated as a wide but short triangle
 * 13) the areas formed when the Earth is furthest from the sun can be approximated as a narrow but long triangle
 * 14) the areas of the two triangles are the same size
 * 15) What are the details of Kepler's law of harmonies?
 * 16) compares the orbital period of and radius of orbit a planet to those of other planets
 * 17) this is a comparison between the motion characteristics of different planets, while the other two are of a single planet
 * 18) law of harmonies compares the ratio of the squares of periods to the cubes of their average distances from the Sun is the same for every one of the planets
 * 19) This value is T^2/R^3
 * 20) this value is also the same for any satellite above any planet
 * 21) Circular Motion Principles For Satellites
 * 22) What is a satellite?
 * 23) Satellites are any object orbiting the Earth, Sun, or any other massive body
 * 24) two types: natural or man made
 * 25) What is the fundamental principal of satellites?
 * 26) satellites are projectiles
 * 27) in orbit, the only force governing the motion of satellites is gravity
 * 28) Newton was the first to conclude that a projectile launched with sufficient speed would orbit the Earth
 * 29) if a projectile was launched with sufficient speed at a correct angle, it would fall towards the Earth at the same rate that the Earth curves
 * 30) at higher speeds, it would orbit the Earth in an elliptical pattern
 * 31) What does a satellite need to orbit the Earth?
 * 32) for every 8000 meters measured along the horizon of the Earth, there is a 5 meter downward curve
 * 33) a projectile must travel horizontally a distance of 8000 meters for every 5 meters of vertical fall
 * 34) the vertical distance a projectile falls in the first second is approx 5 meters, or .5*g*t^2, at 8000 m/s
 * 35) this is assumed that the projectile is launched above the surface of the Earth and encounters little atmospheric drag
 * 36) What are the velocity, acceleration, and force vectors of a satellite?
 * 37) velocity = directed tangent to the circle at every point along its path
 * 38) acceleration = directed towards the center of the circle, towards the central body it's orbiting
 * 39) acceleration is caused by a net force directed inwards in the same direction as the acceleration
 * 40) centripetal force = supplied by gravity, holds the object in orbit (or it would follow an inertial straight path)
 * 41) What are the elliptical orbits of satellites?
 * 42) central body is located at one of the foci of the ellipse
 * 43) velocity = directed tangent to the eclipse
 * 44) acceleration = directed towards the focus of the ellipse
 * 45) net force = directed in the same direction as the acceleration, towards the focus. It is supplied by the force of gravitational attraction between the central body and the orbiting satellite
 * 46) in elliptical paths, the component of force in the same direction as (or opposite) the motion of the object
 * 47) Mathematics of Satellite Motion
 * 48) What are the mathematics of satellite motion?
 * 49) the mathematics of satellite motion are governed by Newton's laws
 * 50) same as the mathematics for circular motion
 * 51) Satellite with the mass Msat orbiting a central body with the mass Mcentral
 * 52) net centripetal force would be the same as in circular motion questions
 * 53) net centripetal force is the result of the gravitational force that attracts the satellite towards the central body
 * 54) **Fgrav = ( G • Msat • MCentral ) / R2 **
 * 55) Fgrav = Fnet, so
 * 56) **(Msat • v2) / R = (G • Msat • MCentral ) / R2 **
 * 57) Mass is present in both sides, so M cancels out to leave
 * 58) **v2 = (G • MCentral ) / R **
 * 59) After taking the square root of both sides, the equation is
 * 60) [[image:http://www.physicsclassroom.com/Class/circles/u6l4b5.gif width="155" height="54" align="bottom"]]
 * 61) acceleration of a satellite in circular motion about a central body is also the same as
 * 62) [[image:http://www.physicsclassroom.com/Class/circles/u6l4b6.gif width="120" height="47" align="bottom"]]
 * 63) Period of a satellite (T) and the mean distance from the central body (R) are related with the equation:
 * 64) [[image:http://www.physicsclassroom.com/Class/circles/u6l4c1.gif width="137" height="55" align="bottom"]]
 * 65) in all the equations, there is no variable Msatellite

=Lesson 4 (D-E), Method 4=
 * 1) Weightlessness In Orbit
 * 2) What is the difference between contact and non-contact forces?
 * 3) Two categories - contact forces and action-at-a-distance forces
 * 4) Contact force - only result from the actual touching of two interacting objects
 * 5) Action-at-a-distance force - the force of gravity acting upon your body is not a contact force
 * 6) Fg is a result of the center of your mass and the Earth's center of mass exerting a mutual pull on each other, force wouldn't exist if you weren't in contact with the earth
 * 7) not contact, so can't be felt through contact
 * 8) never feel Fg in the same way that you would feel a contact force
 * 9) Contact can be felt, action-at-a-distance can never be felt
 * 10) No upward force = no feeling of weight, without contact force, there is no feeling of the non-contact force (gravity)
 * 11) What is the meaning and cause of weightlessness?
 * 12) Weightlessness = a sensation experienced by the individual when there is no external objects touching one's body and exerting a push or pull upon it
 * 13) exists when no contact forces are present
 * 14) occur when you're momentarily in a state of free fall
 * 15) common at amusement parks - as the coaster falls, you and it are both accelerating at the same rate (g), and the chair doesn't push upon you
 * 16) only a sensation, not actually weightless
 * 17) What are the differences between scale readings and weight?
 * 18) scale = measure of upward force applied by the scale to balance the downward force of gravity acting on an object
 * 19) when an object is at equilibrium, these two forces are balanced
 * 20) upward force from the scale = downward force of the pull of gravity (weight)
 * 21) Otis L. Evaderz experimented with weight in a moving elevator
 * 22) normal force > gravity when there is upward acceleration -normal weight sensation
 * 23) N < Fg when there is downward acceleration - more than normal weight sensation
 * 24) N = Fg when there is no acceleration - less than normal weight sensation
 * 25) Are you weightless in orbit?
 * 26) Earth-orbiting astronauts are weightless for the same reason that roller coasters feel weightless
 * 27) no external contact force pushing or pulling upon their body
 * 28) Fg is the only force, and since it is action-at-a-distance, it isn't felt
 * 29) Although gravity is less in space, which means weight is less, but doesn't account for the lack of weight
 * 30) Gravity in space and not air because gravity and air pressure are two separate things
 * 31) Energy Relationships For Satellites
 * 32) What is the energy relationship for a satellite?
 * 33) satellites orbiting Earth have a constant speed at a constant height over the Earth
 * 34) moves with a tangential velocity that allows it to fall at the same rate at which the Earth curves
 * 35) Fgrav is acts in a direction perpendicular to the direction the satellite is moving
 * 36) perpendicular components of motion are independent of one another, so the inward force can't affect the magnitude of the tangential velocity
 * 37) satellite orbiting Earth will experience a component of force in the same or opposite the direction of its motion
 * 38) as it moves from Earth, the component of force is in the opposite direction of its motion, because force does negative work, causing it to slow down
 * 39) when moving towards the Earth, component of force is in the same direction as motion, because force does positive work, causing it to speed up
 * 40) What is the work-energy theorem?
 * 41) initial amount of total energy (TMEi) of a system plus the work done by external forces (Wext) on that system is equal to the final amount of total mechanical energy (TMEf) of the system
 * 42) expressed as
 * 43) KEi + PEi + Wext = KEf + PEf
 * 44) since gravity is an internal force, Wext = 0
 * 45) total amount of energy in the system is conserved
 * 46) sum of potential and kinetic energies is unchanging - the total amount of mechanical energy is the same
 * 47) How do we analyze circular orbits?
 * 48) Satellites remain in the same place above the Earth because they're in circular motion (fixed radius)
 * 49) kinetic energy is also the same regardless of position in circular motion because it is dependent on speed
 * 50) potential energy is dependent on height, so it will be constant
 * 51) if KE and PE are constant, so is TME
 * 52) Work energy bar chart
 * 53) A WEBC is used to represent the amount and type of energy possessed by an object
 * 54) length of the bar represents the amount of energy
 * 55) [[image:http://www.physicsclassroom.com/Class/circles/u6l4e3.gif]]
 * 56) How do we analyze the energy of an object in elliptical orbits?
 * 57) energy of a satellite in elliptical motion will change forms, because Fgrav will change the speed of the satellite as it changes distance above the Earth, so kinetic energy will change
 * 58) Speed = greatest when closest to the Earth, and lowest when furthest from the Earth
 * 59) throughout the entire trajectory, total mechanical energy is always the same
 * 60) Newton's laws apply in space as well