Physic

• Density


  The property of an object that only changes when the substance is heated or cooled
• Sinking and floating


  • An object sinks if its density is more than the liquid on which it is placed, but floats if less dense
• When there is no air resistance the acceleration of any object is constant (constant= 10m/s)
• Easier to lift an object on the moon because gravity is less on the moon and there is no air resistance
• Resultant Force


  The force that results from combining multiple forces
• Types of forces


  • Gravitational
  • Electrostatic
  • Magnetic
• Forces


  • A force applied on an object can cause a change in speed, direction and shape
• Vector quantity


  Quantities like acceleration, velocity etc. that have both magnitude and direction
• When an object moves in a circle it is accelerating and at constant speed at the same time; because the direction is changing but the speed is constant
• Centripetal force


  The force that causes an object to move in a circular path, e.g. tension in a string, gravity, friction
• Equilibrium


  • For an object to be in equilibrium state the resultant force has to be equal or zero (forces up = forces down) and the resultant moment has to equal zero (clockwise moment = anticlockwise moment)
• Stability


  • For the stability of an object it has to have a wide base and a low center of mass
• Finding the center of mass


  Draw two points A and B, hang the object from each hole so that it can swing freely, tie a weight to each point then draw the vertical line, the center of gravity is where the lines intersect
• When a car is going up a hill

  K.E. = Same, G.P.E = Increases, Chemical Energy (petrol) = Decreases and the total energy stays the same as energy is not lost, created or destroyed
• Internal energy


  Thermal energy
• Fission


  Power stations, Large molecules --> Small molecules
• Fusion


  Sun, Small molecules --> Large molecules
• The mass lost is converted into heat energy
• Barometers


  • The space at the top is a vacuum, because air would prevent the mercury from rising
  • The width of the barometer does not affect the height of mercury
• Water manometers


  More accurate to measure gas pressure
• Getting total pressure


  Remember to add the atmospheric pressure
• Converting gas pressure from mm of Hg to Pa

  Use P = density*gravity*height, but remember to use the total pressure
• The more the area


  The more the force
• The less the area


  The less the force
• Pressure in containers


  • The pressure is the same on all the walls as the molecules move in a random motion
• Temperature


  Proportional to K.E. + Molecules hit the walls harder and more often
• Brownian motion


  The tiny, fast-moving air molecules, which are in a constant random motion, are hitting the larger smoke particles from all directions
• Evaporation


  The vaporization of liquid, when the fast moving molecules/energetic molecule leave the surface without the temperature reaching its boiling point
• The greater the surface area, the more the evaporation of particles
• Evaporation vs Boiling


  • Evaporation occurs at surface of liquid: no bubbles
  • Boiling occurs throughout the liquid: bubbles appear
• We feel cold after bath because the high energetic molecule evaporate leaving behind, dull/less energetic molecules
• Thermal expansion


  Molecules gain kinetic energy and force results in pushing each other further apart
• Volume = less area so the particles hit the walls harder and more often
• Mercury and Alcohol thermometers

  • Mercury is used to measure high temperature
  • Alcohol is used to measure low temperatures
• Thermometers


  • The capillary tube is narrow so a small change in temperature results in a large change in volume of the liquid
• Thermocouples


  • Have a low specific heat capacity so they can measure rapidly changing temperatures and they don't take much heat away from the object they are measuring the temperature of
• During melting or boiling the temperature stops rising because extra energy is needed, which is taken from the heat source, to overcome the strong forces of attraction which are holding the molecules together. This energy will not increase the speed of the molecules it will only break the bonds
• In an experiment the value for the latent heat of fusion is too low as energy is taken in from the surroundings which melt the ice
• In an experiment the latent heat of vaporization is too high as energy is lost to the air from the heater therefore not all the energy is used for evaporating the water
• The value for the latent heat of vaporization is much higher than the value for fusion because a large amount of energy is needed to break the bonds between the molecules to move them far apart