Physics GHSGT Review Speed and Velocity Speed distance

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/s 2 • 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 1 st 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 2 nd Law of Motion • Force = mass x acceleration F = ma

Newton’s 3 rd 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/apple ts/doppler 2. html http: //www. colorado. edu/physics/2000/apple ts/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 Mc. Donald 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 1/4 th left)