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STAAR REVIEW Physics
Newton’s 3 Laws of Motion • Law of Inertia: A body at rest wants to remain at rest, a body moving in motion wants to continue in motion unless acted on by an outside force. • Force = mass x acceleration • For every action there is an equal and opposite reaction.
Newton’s First Law of Motion Objects at rest will remain at rest (an object in motion will remain in constant motion) unless an unbalanced force acts on it. Law of Inertia Reason we wear seatbelts
Newton’s Second Law of Motion Force = mass x acceleration Force exerted by an object is equal to its mass times its acceleration Weight = mass x acceleration due to gravity (9.8 m/s2) Weight changes due to gravity (mass does not)
Newton’s Third Law of Motion For every action force there is an equal but opposite reaction force. Do not cancel each other out – act on different objects
Formula Chart • Density = mass/volume • Speed (Velocity) = distance/time • Force = mass x acceleration • Work = force x distance YOU WILL HAVE A FORMULA CHART USE IT!!
Energy The ability to do work or to cause change
Potential vs Kinetic Energy • Kinetic Energy = energy of motion • Potential Energy = stored energy • Kinetic Energy = ½ (mass x velocity2) • Potential Energy = mass x acceleration(gravity)x height Looking at the following formulas, determine what variable effects each type of energy the most. (Hint: use some simple numbers in the formulas).
Potential (PE) Potential Energy Stored energy
Kinetic Energy (KE) Energy due to motion of an object Did you know that the gas burned in a car engine is chemical energy being turned into Kinetic Energy? Kinetic energy Rubber band flying through the air has kinetic energy Speed & mass affect kinetic energy– Faster/heavier…more Kinetic Energy
Before the yo-yo begins its fall it has stored energy due to its position. At the top it has its maximum potential energy. As it starts to fall the potential energy begins to be changed into kinetic energy. At the bottom its potential energy has been converted into kinetic energy so that it now has its maximum kinetic energy A waterfall has both potential and kinetic energy. The water at the top of Bridal Veil Falls has stored potential energy. When the water begins to fall, its potential energy is changed into kinetic energy. This change in energy also happens at Niagara Falls where it is used to provide electricity from the transformation of mechanical and electromagnetic energy.
Chemical Energy Electrical Energy Sound Energy ENERGY Solar Energy Heat Energy Nuclear Energy Mechanical Energy
Energy stored in bonds between atoms in molecules When bonds are made or broken in chemical reactions energy is either absorbed (endothermic) or released (exothermic) 6H2O + 6CO2 + sunlight (energy) → C6H12O6 (sugar = stored energy) + 6O2 Chemical Energy
Electrical Energy Produced when electrons flow through materials (can jump from one place to another) Light and heat given off from a lamp is the result of electricity conversion
Heat Energy Heat of a substance is the average kinetic energy of the particles of a substance Warmer substances have more kinetic energy Conduction – heat energy transfers when particles with greater kinetic energy collide with less-energetic particles – move from hot (high energy) to cold (low energy) Convection – transfer of heat energy by the movement of a substance On a sunny day the land will heat up faster than the water due to specific heat Radiation – no physical contact needed, increase in kinetic energy of particles by interaction of electromagnetic waves
Mechanical Energy KINETIC ENERGY Gravitational POTENTIAL ENERGY Energy of motion Depends on object’s speed and mass Energy of position Or Stored energy Depends on mass and distance away from the pulling object
Nuclear Energy Energy found within the nucleus of an atom Can be released during fusion or fission
Solar Energy Energy from the Sun Visible Light Infrared Ultimate source of energy on Earth
Sound Energy Mechanical Compressional (Longitudinal) Wave Needs a medium (matter) to move the energy Travels faster through a solid than a gas
Energy • Energy is the ability to do work or cause change • Energy transformation is the change from one energy form to another for example: • Your car changes chemical energy into mechanical energy • Your electric stove changes electricity into thermal energy • A plant uses solar energy and changes it into chemical energy
Potential energy A rock sitting at the top of a cliff Roller coaster car at the top peak of a hill A swimmer posed to dive off the end of a diving board NO MOTION !! Kinetic energy A bouncing ball A moving roller coaster A track star running A girl skiing MOTION is the key!!!! Energy Transformations
Chemical Energy – Energy transformations Chemical energy – when light energy from the sun is converted to the energy in the bonds of the sugar molecules formed in photosynthesis.
Chemical Energy Examples of chemical energy changing into heat energy: Lighting a match Burning a wood fire
Heat energy- Energy transformations • Heat energy – energy is absorbed and temperature rises. • Specific heat- the ability of a substance to absorb heat energy
Specifics of Specific Heat Water Holds Thermal Energy at Lower Temperature Temperature is a measure ofthe average kinetic energyof the molecules in the object.-----------------------------------------Will both fingers feel the same temperature when they'reput in the warm water?
Electrical energy- Energy transformations Electrical energy- flow of electrons (a current) • Other ways of generating electricity: • Water flowing through a dam in a river to move turbines • Wind generators that use the energy of moving wind & operate a generator • Nuclear power plants convert atomic energy into heat. Heat boils water to form steam & then follows the same energy transformations as coal power plants
Many energy transformations… Electrical to mechanical: Electricity used to spin the CD (Spinning CD has mechanical energy due to its position or motion) Electrical to sound: A laser converts the digital information on the CD into electrical energy and this energy goes to the headphones as a vibration- this transmits Sound! Chemical to electrical: Batteries store chemical compounds that react when they are used to power something. This produces a flow of electrons which is electricity!!
Sound energy- Energy transformations Sound – consists of mechanicalenergy waves created by vibrations. Sound must travel through something (called “medium” or “media”) such as air, water, or a solid. The medium carries the energy of the wave from one place to another. Example: Air transmits the energy of the vibrating material in the headphones to your eardrums. A vacuum is a space that contains little or no matter. Sound can’t travel through a vacuum since there are no particles to squeeze together (compression) or spread apart (rarefaction)
Many times it takes a whole series of energy conversions to do a certain job. For example, just to get the energy to make a piece of toast, there are several energy conversions involved. • Chemical energy stored in coal is released as heat and light energy when the coal is burned. The heat energy is used to produce steam and is changed into mechanical energy in a generator. The generator converts mechanical energy into electrical energy that travels through power lines into your home. When you use your toaster, that electrical energy is again changed into heat energy. • Have you ever touched a light bulb when it was on? Or tried to change it when it burnt out after being on? What you have discovered is the conversion process of energy- When you turn on a light, not all of the electricity is converted to light energy. Some of the energy is converted to heat. Remember, energy is never lost- it’s only converted from one form to another. This is the law of conservation of energy
Sources of Energy • Renewable • Nonrenewable • Inexhaustible
Renewable Energy Resources Resources that can be replaced in short amount of time Examples:, geothermal, biomass (plant or animal products that can be used to produce energy – like corn and methane from cows)
Nonrenewable Energy Resources Resources that nature cannot replace within a human life span Example: fossil fuels like coal, oil, and natural gas
Inexhaustible Resources Inexhaustible resources, will always be around during our lifetime. Examples include solar, wind & hydroelectric (water)
Ability to do work Work is done when a force is applied to matter Travels in Can be transformed (converted) but not created = Law of Conservation of Energy Energy WAVES
Waves • Reflection • Refraction • Diffraction
Reflection light tends to travel in a straight line, unless it is acted on by some external force or condition. Reflection light bounces off of a surface and starts traveling abruptly in a different direction.
Refraction Refraction of waves involves a change in the direction of waves as they pass from one medium to another. Refraction, or bending of the path of the waves, is accompanied by a change in speed and wavelength of the waves.
Diffraction Diffraction involves a change in direction of waves as they pass through an opening or around a barrier in their path. Waves have the ability to travel around corners, around obstacles and through openings.
Light waves do not need a medium to transmit energy! They can even travel through empty space. Light Waves
Water waves are a form of a wave that transmits mechanical energy across the surface of water. Water waves A wave is a disturbance that transfers energy from one place to another.
Do you have potential? Seismic waves – forces build up within the Earth and once the energy is released – Falling Water - EARTHQUAKE
Seismic waves Seismic waves are caused by earthquakes that transmit mechanical energy through the Earth’s layers. San Andreas Fault
Waves Mechanical Electromagnetic Must travel through a medium Example: Sound Seismic Water Compressional Transverse Does NOT need a medium; Can Travel through a vacuum Examples: Light Ultra-violet Infrared Radio Microwaves Gamma
Draw & Label a Wave Wavelength – length of one wave; measured from crest to crest or trough to trough Crest – highest point on the wave Amplitude – related to the amount of energy Rest Trough – lowest point on the wave
Frequency = High Frequency = Low Frequency How many times a particle moves from its original position
Force pushing or pulling action that may change motion Forces may transfer energy between objects Forces may MOVE objects
A book resting on a desk illustrates balanced forces. However, a book dropped from a desk illustrates unbalanced forces. In this case, gravity has overcome the balance of forces.