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The Scientific Method • 1. Observe some aspect of the universe. • 2. Invent a tentative description, called a hypothesis, that is consistent with what you have observed. • 3. Use the hypothesis to make predictions. • 4. Test those predictions by experiments or further observations and modify the hypothesis in the light of your results. • 5. Repeat steps 3 and 4 until there are no discrepancies between theory and experiment and/or observation.
Science versus Pseudoscience • The scientific method is unprejudiced. • A theory is accepted based only the results obtained through observations and/or experiments which anyone can reproduce. • The results obtained using the scientific method are repeatable. • a theory must be ``falsifiable''. • Pseudoscience, in contrast, does not employ the scientific method and is constructed in such a fashion that its claims are not falsifiable
System of Units • Scientific International (SI) • Based on multiples of 10 • meter (m) distance length of the path travelled by light in vacuum during a time interval of 1/299 792 458 of a second. • kilogram (kg) mass mass of the international prototype of the kilogram. • second (s) time the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of Cs 133 • ampere (A) electric current current, if maintained in two straight parallel conductors of infinite length, of negligible circular cross-section, and placed 1 meter apart in vacuum, would produce between these conductors a force equal to 2 × 10-7 newton per meter of length." • kelvin (K) temperature the fraction 1/273.16 of the temperature of the triple point of water."
Scalars and Vectors • A scalar quantity has magnitude only (how much?) • Examples • Mass • Volume • Distance • Speed • A vector quantity has magnitude and direction • Examples • Displacement • Velocity • Acceleration • Force
Aristotle’s Universe(Geocentric) • Aristotle proposed that the heavens were literally composed of concentric, crystalline spheres to which the celestial objects were attached. • Each object rotated at different velocities, with the Earth at the center. • The ordering of the spheres to which the Sun, Moon, and visible planets were attached are shown to the right.
Stellar Parallax • Stars should appear to change their position with the respect to the other background stars as the Earth moved about its orbit, because they are viewed from a different perspective.
Planetary Motion • Most of the time, planets move from west to east relative to the background stars. This is direct motion. • Occasionally, however, they change direction and temporarily undergo retrograde motion before looping back. • (retrograde-move)
Planetary Motion-2 • Retrograde motion was first explained using the following model devised by Ptolemy: • The planets were attached, not to the concentric spheres themselves, but to circles attached to the concentric spheres, as illustrated in the adjacent diagram. • These circles were called "Epicycles",and the concentric spheres to which they were attached were termed the "Deferents".
Planetary Motion-3 • In actual models, the center of the epicycle moved with uniform circular motion, not around the center of the deferent, but around a point that was displaced by some distance from the center of the deferent.
Heliocentric Model • Copernicus proposed that the Sun, not the Earth, was the center of the Solar System. Such a model is called a heliocentric system. • The ordering of the planets known to Copernicus in this new system is illustrated in the following figure, which we recognize as the modern ordering of those planets. (copernican-move)
Galileo Galilei • Galileo used his telescope to show that Venus went through a complete set of phases, just like the Moon. This observation was among the most important in human history, for it provided the first conclusive observational proof that was consistent with the Copernican system but not the Ptolemaic system.
Kepler- Elliptical orbits • The amount of "flattening" of the ellipse is the eccentricity. In the following figure the ellipses become more eccentric from left to right. A circle may be viewed as a special case of an ellipse with zero eccentricity, while as the ellipse becomes more flattened the eccentricity approaches one. • (eccentricity-anim)
Kepler’s Laws • Kepler’s 1st Law: • The orbits of the planets are ellipses, with the Sun at one focus of the ellipse.
Kepler’s Laws • Kepler’s 2nd Law: • The line joining the planet to the Sun sweeps out equal areas in equal times as the planet travels around the ellipse.
Kepler’s Laws • Kepler’s 3rd Law: • The ratio of the squares of the revolution periods (P) for two planets is equal to the ratio of the cubes of their semimajor axes (R).
Speed “How fast/ How slow is it going?” Time rate of change of motion: Speed = distance time
Constant Motion vs. Changing Motion • Object’s motion is constant: its speed and direction are not changing • Object’s motion is changing:its speed and/ or direction are changing
Acceleration “Is it speeding up, is it slowing down, How fast is its speed changing?” More important: “How is its motion changing?”
Acceleration (con’t) Acceleration = change in velocity time a = vf - vi t or a = v t
Acceleration Due to Gravity Some everyday observations . . . ~ an object’s velocity increases as it falls ~ how an object’s velocity changes depends on air resistance If there is no air resistance, the object will fall freely . . . We call it a Freely Falling Object
Motion with Constant Acceleration Recall: a = vf - vi t When the objects initial velocity is zero . . . We say that it started from rest Or was dropped from rest vf = a t d = ½ at2 and
Motion in a Circle • Recall that acceleration is defined as a change in velocity with respect to time. • Since velocity is a vector quantity, a change in the velocity’s direction , even though the speed is constant, represents an acceleration. • This type of acceleration is known as Centripetal acceleration ac = v2/r
Force & Motion • Force everyday words: Push or Pull Examples: (Earth’s Gravity pulls down on objects) • Forces are Vectors
Recognizing Forces Note: The Force due to Gravity is always pulling down on us! • At-a-Distance Forces & Contact Forces
The sum of all the forces acting on an object Net Force: Net force zero: Balanced forces Net force non-zero: Unbalanced forces
Newton’s Laws of Motion (Net) force causes change in motion Net Force Change in Motion Cause Effect
Newton’s 1st Law of Motion: The Law of Inertia An object at rest, or in motion, will stay at rest, will continue in the same (straight –line) motion, unless a net, external force acts on it. unbalanced outside
Better!:For every force one object exerts onto another, there is an equal & opposite force exerted back. Newton’s 3rd Law of Motion Warning: This popular expression of Newton’s 3rd Law can lead to confusion!!!! “For every action - there is an equal and opposite reaction.”
F = ma Newton’s 2nd Law of Motion Force = mass x acceleration
Weightis the force due to gravity on an object Relationship between Mass & Weight w = Fg = mag w = m g ag
Product of the mass and velocity of an object Momentum = mass x velocity Momentum p = mv
When two objects collide Law of Conservation of Linear Momentum: The total linear momentum of an isolated system remains the same: if there is no external, unbalanced force acting on the system. Conservation of Momentum (exerting forces on each other), their total momentum is conserved
Law of Conservation of Angular Momentum The angular momentum of an object remains constant, if there is no external, unbalanced torque acting on it. Conservation of Angular Momentum Angular Momentum:The momentum of rotation
Does the rotation of the Earth cause gravity? Gravity Does the our atmosphere/ air pressure push us down to keep us on the ground? Does the Moon’s orbit about the Earth cause gravity? Is there gravity on the Moon? On the Sun? Are the astronauts in the space shuttle really weightless?
Every mass in the universe attracts (and is attracted by) every other mass in the universe by a force that we call the force of gravity. Equation form of this law: Law of Gravity: (where G = 6.67 x 10-11 Nm2/kg2)
(Sometimes called “microgravity”) Apparent weightlessness: the sensation you experience when there is no floor pushing up on you. Weightlessness
the process by which energy is transferred or changed from one form into another “It takes energy to do work” Work • Work is done when you apply a force over a distance W = F x d
- the energy an object has because of its location (in a force field) “position energy” Gravitational Potential Energy: Work Energy sugar in muscles PotentialEnergy of ball Work I did lifting = PEball PE = mgh mag F d = PE g
- the energy an object has because of its motion “moving energy” Kinetic Energy, KE KE = ½ mv2 Ex: Basketball Ball KineticEnergy of ball Work I do pushing
In the absence of friction: the sum of the kinetic energy and the potential energy of a system is constant. (I.e., total energy is constant!) Law of Conservation of Mechanical Energy
Power = work time Power - time rate of energy usage “How fast was the work done?” P = W t Units: Watts = Joule/sec
Thermal Energy (Heat) • Heat is simply thermal energy; i.e., a measure of the kinetic energy of the atoms or molecules that make up a substance. • Heat Energy is measured in calories—defined as the heat required to raise 1 gram of water by 1 o C. • The mechanical equivalent(in joules) of a calorie is : 1 calorie = 4.186 Joules
Mass Energy • Every object contains the (mass)potential energy equivalent : • E = m c2 • where c is the speed of light • c = 3 x 108 m/s
Relativity Revealed 1′ Lecture: • The Special Theory of Relativity tells us that time, distance and mass are not what we think they are. • The General Theory of Relativity shows us that mass warps space.
Relativity Revealed Special Theory • Applies to non-accelerated “frames of reference.” • Makes two (2) assumptions: • The is no preferred inertial frame of reference. • The velocity of light, c is a constant.
Relativity Revealed What about assumptions? • No preferred inertial frame. • Speed of light is constant. (c = 300,000,000 m/s) O.K. ☑ ??????
Relativity Revealed It’s everywhere! It’s everywhere! The Lorentz Factor: 1/√[1 - v 2/c 2 ] Not important until v ≈ c, then VERY important.
Fundamental Principles of Temperature & Heat • Matter is made up of particles • and these particles are in motion • Heat energy naturally “flows” • from warmer parts to cooler parts of a system • Conservation of (Heat)Energy • (First Law of Thermodynamics) Heat Energy lost + Heat Energy gained = 0
“Particles are in motion” Microscopic Properties of Substances • Particles are moving in all directions! • Particles are colliding with each other & the walls of the container! Temperature, T, is a relative measure of the average KE of the particles.
Heat Transfer Mechanisms 1. Conduction: Transfer of heat by individual particles colliding with each other 2. Convection:Transfer of heat by the large scale movement of heated regions of a fluid to cooler regions 3. Radiation:Heat transfer by the absorption or emission of EM radiation (mainly infrared radiation)