4TH ESO Chemistry and Physics IES AMES WORK HEAT WAVES

And what is a man without energy? Nothing - nothing at all. Mark Twain

ENERGY CAN EXIST IN DIFFERENT FORMS

In physics, work is done only when an object is moved in the direction of the applied force. Work is defined as the scalar product of the force applied and the distance moved by the object. S.I. unit: Joule

In physics, power is the time rate of doing work or, the amount of work done per second. P= W / t Instantaneous power: P= F.v SI unit of power is the watt (W) or joule per second (J/s). Horsepower is a unit of power in the British system of measurement 1 horsepower= 736 W

Kinetic energy is the energy of motion. The kinetic energy of an object is the energy it possesses because of its motion. KE = ½ mv 2. WORK-ENERGY THEOREM WORK-ENERGY THEOREM: Relation between KE and W: The work done on an object by a net force equals the change in kinetic energy of the object: W = KEf - KEi.

An object can store energy as the result of its position. This stored energy of position is referred to as potential energy. Potential energy is energy which results from position or configuration. - An object may have the capacity for doing work as a result of its position in a gravitational field (gravitational potential energy) or in an electric field (electric potential energy) - It may have elastic potential energy as a result of a stretched spring or other elastic deformation.

One way to state this principle is "Energy can neither be created nor destroyed". Another approach is to say that the total energy of an isolated system remains constant. Ei = Ef or Ki + Ui = Kf + Uf

In thermal physics, thermal energy is the energy portion of a system that increases with its temperature. INTERNAL ENERGY: the sum of all microscopic forms of energy of a system. It is related to the molecular structure and the degree of molecular activity and may be viewed as the sum of kinetic and potential energies of the molecules When an object is heated, its internal energy increases. Like all other forms of energy, internal energy is measured in J (joule).

SPECIFIC HEAT CAPACITY The specific heat capacity of a substance is the amount of energy (in joules) that is needed to raise the temperature of 1 kg of the substance by 1 ºC. ENERGY NEEDED/RELEASED = m c e  t mass x specific heat capacity x change in temperature

TRANSFERRING HEAT CONDUCTION: Regions of greater molecular kinetic energy will pass their thermal energy to regions with less molecular energy through direct molecular collisions. CONVECTION: Free convection. Heat-induced fluid motion in initially static fluids (liquid or gas). If the static fluid is heated, it loses density and rises. If cooled, it will become dense and sinks. It is a gravity gradient that induces motion through buoyancy. Forced convection. When the fluid is already in motion, heat conducted into the fluid will be transported away mainly by fluid convection. Pressure gradient forces drive the fluid motion. RADIATION: Transfer of heat by electromagnetic radiation. Thermal energy is radiated at wavelengths determined by the temperature of the surface-short wavelengths for the sun and long wavelengths for sun-warmed materials such as brick. Bright, shiny materials reflect radiation while dull, black materials absorb it.

Webster's dictionary defines a wave as "a disturbance or variation that transfers energy progressively from point to point in a medium and that may take the form of an elastic deformation or of a variation of pressure, electric or magnetic intensity, electric potential, or temperature.“ Waves travel and transfer energy from one point to another, often with little or no permanent displacement of the particles of the medium (that is, with little or no associated mass transport); instead there are oscillations around almost fixed positions.

QUANTITIES AMPLITUDE (m) The amplitude is the height of the wave. WAVELENGTH (m) The wavelength is the distance between two successive crests (or troughs) PERIOD (s) The period of a wave is the time for a particle on a medium to make one complete vibrational cycle FREQUENCY (cycles/s or Hz) Frequency refers to how many waves are made per time interval. This is usually described as how many waves are made per second, or as cycles per second.

QUANTITIES SPEED (m/s) The speed of an object refers to how fast an object is moving and is usually expressed as the distance traveled per time of travel. In the case of a wave, the speed is the distance traveled by a given point on the wave (such as a crest) in a given interval of time. The speed of a wave is a property of the medium - changing the speed actually requires a change in the medium itself. If the medium does not change as a wave travels, the wave speed is constant.

TYPES OF WAVES LONGITUDINAL Figure 1: A longitudinal wave, made up of compressions - areas where particles are close together - and rarefactions - areas where particles are spread out. The particles move in a direction that is parallel to the direction of wave propagation. me/VLObject mov TRANSVERSE Figure 2: A transverse wave. The particles move in a direction that is perpendicular to the direction of wave propagation. ktime/VLObject mov

PROPERTIES fendt.de/ph11e/huygenspr.htm REFLECTION Reflection involves a change in direction of waves when they bounce off a barrier REFRACTION Refraction of waves involves a change in the direction of waves as they pass from one medium to another DIFFRACTION Diffraction involves a change in direction of waves as they pass through an opening or around a barrier in their path.