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Force • What is force? – Push or Pull • It’s what causes “things” to accelerate 1000 kg Balanced v. Unbalanced Forces • If all forces are balanced there is no acceleration in any direction. – (Either Zero Motion or Constant Velocity) • If one force is greater than the opposing force we get acceleration in a direction. Balanced Forces (Balanced Forces = No Acceleration) 5N Object Notice that all the forces are equally pointed in the opposite direction. Hence they balance each other – or cancel each other. 5N Equal Pushing Forces may cancel each other and produce No Acceleration! Balanced Forces (Balanced Forces = No Acceleration) Ground pushes up Gravity pulls down Gravity pulls down on you… The ground pushes back up… THIS KEEPS YOU WHERE YOU ARE! If these football players push on each other equally as hard, will either one move? Balanced Forces (Balanced Forces = No Acceleration) 5N 5N Equal Pushing Equal Pulling 5N 5N Forces may cancel each other and produce No Acceleration! Unbalanced Forces Causes Acceleration Adding Forces Subtracting Forces Adding Forces 5N 5 N = 10 N • Two forces can add together to produce a larger net force than either original force. – Positive Acceleration occurs (Speed up) Unbalanced Forces Causes Acceleration Adding Forces 5N Object 5N Notice that all the forces are pointed in the same direction. Hence they add together. Subtracting Forces 10 N =5N 5N • Two forces can subtract to produce a net force in the direction of the larger force. – Negative Acceleration occurs (Slow Down) Unbalanced Forces Causes Acceleration Subtracting Forces 5N Object 5N Notice that all the forces are unequal and pointed in the opposite direction. Hence they are unbalanced and in opposition to each other – or one partially cancels the other. 5N Balanced Forces 10N 10N 10N Balanced Push i.e. Pushing a Car No Acceleration 10N Balanced Pull i.e. Tug-o-war No Acceleration Un-Balanced Forces Additive 10N 10N Un-Balanced Same Direction Faster Acceleration Un-Balanced Opposite Direction Slower Acceleration Subtractive 10N 10N 10N Balance between Gravity and Friction Q: If the friction of the air and the pull of gravity were in perfect balance, what would the skydiver be doing? A: The skydiver would be going a constant velocity (moving with no acceleration) down towards the ground until it hit the ground. The skydiver is colliding with the molecules of gas in the air! Which slows down the fall of the skydiver! Accelerating Constant Velocity Accelerating Air Resistance 30 m/s 28 25 m/s 20 10 0 m/s Speed: Constant Velocity 0 m/s How it works Notice that as the skydiver leaves the plane, the force of gravity accelerates him faster towards the earth; however, the moment he jumps out of the plane, another force begins to oppose gravity – Air Resistance, (Friction). This friction with the air begins to slow down his rate of acceleration. Meaning, he’s still speeding up, just not as fast. Gravity Once the force of air friction equals the force of gravity, the skydiver steadily descends towards earth at a constant velocity. Balanced Forces (Balanced = No Acceleration ) Wait aForces minute. This object was moving. That’s Right. As you may have noticed, although I may have balanced forces, I might still be moving. Notice that when the forces are balanced, the object might still be moving, but the objects are not accelerating, instead they have a constant velocity. Hence, once in motion – it’s always in motion unless acted upon by what? Another Force. 5N Notice that all the forces are equally pointed in the opposite direction. Hence they balance each other – or cancel each other. Object Equal Pushing Equal Pulling Forces may cancel each other and produce No Acceleration! 0 1 2 3 4 56 Distance [m] Constant Velocity 1 2 4 3 Time [Sec] In other words, you still need to use the gas peddle to balance out all the force of friction to keep you going at a constant speed. 5N 5 Acceleration 1 2 To get an object to move faster, create an unbalanced force! 5N Force • Speed = Distance divided by time • S= D/T • What is the speed of a rocket traveling at 4,000 miles in 1.5 hours? 2,667 miles/hr The Law of Conservation of Energy created or • Energy cannot be __________ ____________; it may be transformed destroyed from one form into another, but the total never amount of energy _________ changes. What is energy? • “the ability to do work” • The combination of energy and matter make up the universe: – Matter is substance, and energy is the mover ____________ of substance. Energy is nature’s way of keeping score. We sense energy only when it changes, either a transformation from one form of energy to another, or a transfer of energy from one point to another. How is all energy divided? All Energy Potential Energy Gravitation Potential Energy Elastic Potential Energy Kinetic Energy Chemical Potential Energy Potential position • energy of _________ or energy in storage ______________. – Water behind a dam – Hammer over head – Food on the plate Kinetic motion • energy of ________, the form capable of doing work – Flowing water – A falling hammer – Food being converted into usable energy in the cell. PE = mgh m = mass (kg) ____ h = height (m) ____ g = accel due ____ to gravity (9.8 m/s2) What is Gravitational Potential o Potential energy Energy? due to an object’s position Don’t look down, Rover! Good boy! mass o P.E. = ________x height x ________ gravity _____________ What is Potential Energy? o Energy that is stored and waiting to be used later What is Elastic Potential Energy? o Potential energy due compression or expansion of an elastic object. Notice the ball compressing and expanding What is Chemical Potential Energy? o Potential energy stored within the chemical bonds of an object What is Kinetic Energy? o Energy an object has due to its motion o K.E. = .5(mass x speed2) KE = 1/2 m v2 • • • • 4 kg bowling ball at 10 m/s = .5 (4kg) (10m/s)2 = 200 J • • • • .25 kg baseball at 50 m/s = .5 (.25kg) (50 m/s)2 = 312 J Courtesy Jerry Ohlinger’s Movie Material Store Work is done when a force is exerted over a distance. Work • is equal to the force that is exerted multiplied by the distance over which it is exerted. Fxd • W = _______ • The unit of work combines the unit of force (N) with the unit of distance (m) Joule • Newton-meter (N-m) aka ________. You carry a 20 kg suitcase upstairs, a distance of 4m. How much work did you do? • W=Fxd • F = ma • = (20 kg) (10m/s2) = 200 N • W=Fxd • = (200 N) (4m) • = 800 J 6 fundamental forms of energy 1. 2. 3. 4. 5. 6. mechanical energy Thermal (heat) energy electromagnetic energy electrical energy nuclear energy chemical energy What is the source of our energy? • The source of practically all our energy is the _______ SUN . What is Mechanical Energy? o Energy due to a motion object’s _________ position (kinetic) or __________ (potential). The bowling ball has mechanical energy. When the ball strikes the pins, mechanical energy is transferred to the pins! Examples of Mechanical Energy What is Electromagnetic Energy? Light energy o _________________ o Includes energy from gamma rays, xrays, ultraviolet rays, visible light, infrared rays, microwave and radio bands What is Electrical Energy? o Energy caused by the movement of electrons _____________ o Easily transported through power lines and converted into other forms of energy What is Chemical Energy? o Energy that is available for release from _____________________. Chemical reactions The chemical bonds in a matchstick store energy that is transformed into thermal energy when the match is struck. Examples of Chemical Energy What is Thermal Energy? o Heat energy o The heat energy of an object determines how active its atoms are. A hot object is one whose atoms and molecules are excited and show rapid movement. A cooler object's molecules and atoms will show less movement. QUIZ TIME! What type of energy cooks food in a microwave oven? ELECTROMAGNETIC ENERGY What type of energy is the spinning plate inside of a microwave oven? MECHANICAL ENERGY QUIZ TIME! Electrical energy is transported to your house through power lines. When you plug an electric fan to a power outlet, electrical energy is transform into what type of energy? MECHANICAL ENERGY QUIZ TIME! What energy transformation occurs when an electric lamp is turned on? ELECTRICAL ENERGY ELECTROMAGNETIC ENERGY What types of energy are shown below? Mechanical and Thermal Energy (Don’t forget friction) What type of energy is shown below? Chemical Energy What types of energy are shown below? Electrical, Mechanical and Electromagnetic Energy What type of energy is shown below? Chemical Energy (yummy) What type of energy is shown below? Thermal Energy What types of energy are shown below? Mechanical, Electromagnetic, Electrical, Chemical and Thermal Energy The Law of Conservation of Energy • Energy cannot be created or destroyed; it may be transformed from one form into another, but the total amount of energy never changes.