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Physics GHSGT Review Speed and Velocity • Speed = distance divided by time s = d/t • Units of speed = m/s • Velocity = speed in a given direction • Example: – 55 mph = speed – 55 mph north = velocity Distance versus Time Graph • AKA position versus time graph • Straight line represents constant (uniform) speed Acceleration • Acceleration = rate at which velocity changes • Involves a change in speed OR direction a = (vf – vi )/ t • Units of acceleration = m/s2 • Example: 0 to 60 mph in 5 seconds • For acceleration to occur a net (unbalanced) force must be applied Distance versus Time Graph Revisited • Non-linear graph represents acceleration • Parabola = constant acceleration Forces • Force = a push or a pull • Net Force = sum of all forces acting on an object • Free-body diagram shows all forces with vector arrows • Direction of force = direction of acceleration • Friction is a force that always opposes motion Determining the Net Force Newton’s 1st Law of Motion – An object at rest will remain at rest and an object in constant motion will remain in constant motion unless acted on by an unbalanced force. – Reason for seatbelts Newton’s 2nd Law of Motion • Force = mass x acceleration F = ma Newton’s 3rd Law of Motion • For every action, there is an equal but opposite reaction • Examples: – Punch a wall, it punches back – Rocket propulsion Gravity • Gravity = attractive force between two objects that have mass • Depends on mass and distance Effects of Mass and Distance on Gravity Momentum • Momentum is mass in motion p = mv • To change an object’s momentum a force must be applied • Conservation of momentum states that momentum before a collision equals momentum after Energy and Work • The ability to do work • Work = transfer of energy by applying a force to move an object W = Fd where force and distance are in same direction • Both work and energy are measured in Joules Examples of Work and No Work • Hammer applies a force to move the nail in the same direction = WORK • Waiter applies a force upward while the tray moves forward = NO WORK Types of Mechanical Energy • Kinetic = energy of motion • Potential = stored energy due to position Conservation of Energy Conservation of Energy Conversion of Energy • Motor = converts electrical energy into mechanical energy – Motors make fans Move which is Mechanical • Generator = converts mechanical energy into electrical energy – Georgia Power use a Generator to provide electricity Power • Power = rate at which work is done P = W/t • Measure in Watts • More work, less time = More Power • Less Work, Long time = Less Power Heat Energy • Heat can be transferred through: – Conduction = when objects touch – Convection = when matter moves – Radiation = in the form of waves • Conductors = easily transmit energy – Example: metals • Insulators = do not easily transmit energy – Example: gases such as air Light • Light is a form of electromagnetic radiation (EM) • EM spectrum shows the forms of radiation in order of increasing frequency and decreasing wavelength Energy of a Wave • The energy transferred from a vibrating source is carried by a disturbance in the medium, not by matter moving from one place to another. – Waves move ENERGY, not matter • Energy carried by a wave consist of KE and PE Parts of Wave • The dashed lines represent the equilibrium • The crests are the highest parts of the wave (letters A and F) • The troughs are the lowest parts of a wave (letters D and I) • Wavelength is the distance from crest to crest (A to F) or trough to trough (D to I) • Amplitude is the distance from the midpoint to the crest Wavelength crest trough Wavelength Transverse Waves Transverse wave: a wave with a vibration at right angles to the direction the wave is traveling. The energy moves through the medium left to right, but the motion of the wave is up and down Makes an “S” shape wave Ex: light waves, string instrument Longitudinal Waves Longitudinal wave: a wave in which the vibration is in the same direction as that which the wave is traveling. Both the energy motion and the movement of the wave are left to right Makes a pulse through the wave Ex: sound waves, earthquake waves Doppler shift • The doppler shift a a change in frequency of a wave based on the movement of the observer or the source – Ex: a siren changing pitch as it moves towards or away from you http://www.colorado.edu/physics/2000/applet s/doppler2.html http://www.colorado.edu/physics/2000/applet s/doppler.html A Sound Wave • Sound waves are longitudinal waves. • Parts of a sound wave: 1) Compression: areas of high pressure 2) Rarefaction: areas of low pressure • As a source vibrates in a periodic fashion, a series of compressions and rarefactions is produced • For all wave motion, it is not the medium that travels across the room, but a pulse (or energy) that travels. • The speed of sound varies in different media. In general, sound is transmitted faster in liquids than in gases, and still faster in solids. • Remember that sound DOES NOT travel through a vacuum The EM Spectrum • All of the EM waves are the same in nature, differ only in the wavelength and frequency “Ronald McDonald Is Very Ugly X-tra Gross” • The speed of light is constant when it travels through one type of medium. – Light travels faster in air than in water. – Molecules in its way slows light down – It is the opposite of sound waves, which require a medium to move faster • Light travels the fastest in a vacuum and slowest in a solid – The more molecules in its way, the slower it goes – Vacuum > G > L > S Color of Light • We see different colors depending on the frequency of light emitted or reflected • This is the reason blue flames are hotter than yellow. Blue has a higher frequency so more energy. Mixing Colored Light • Light of all the visible frequencies mixed together produces white light. • White light can also be produced by mixing red, blue, and green light. – Red, blue, and green are the 3 primary colors of light. • Color T.V.s produce all the colors we perceive by combining red, blue, and green light in a variety of ways. Adding Primary Colors • • • • Red + Green = Yellow Red + Blue = Magenta (Purple) Blue+ Green = Cyan (Aqua) Red + Blue + Green = White Refraction of Light • Light waves travel faster in air than in water and slower in glass than water. • More dense = slower light • When light enters a different medium, speed changes and it bends. • Bending of light due to change in speed = REFRACTION Electricity • • • • Electrons carry a negative charge. Lost electrons = positive charge Gained electrons = negative charge REMEMBER: – Like charges repel – Opposites attract • An object can be charged through: – Friction (rubbing two objects together) – Conduction (touching a charged object to an uncharged object) – Induction (holding a charged object near an uncharged object) Electrical Circuits SERIES • Current flows in a closed circuit • Ohm’s Law – V = IR • Two types of circuits: – Series (single path) – Parallel (poly paths) PARALLEL Electromagnet • One can make an electromagnet with a nail, battery, and wire • When current flows through the coiled wire, the nail becomes magnetized. Electromagnetic Induction • Occurs when a current is produced by moving a conducting wire through a magnetic field Radioactive Half-Life Half-life: The time required for half of the atoms of a radioactive isotope of an element to decay. – Radioactive isotopes decay at different rates – The amount of a substance halves every halflife – Ex: If the half life of an isotope if 10 years, then after 10 years there is only half left. After 20 years, there is only half of that half (or 1/4th left)