Physics paper 1

• System


  An object or group of objects
• When a system changes

  The way energy is stored also changes
• Ball rolling and hitting a wall


  • System is moving ball
  • When it hits the wall, (some of) the kinetic energy is transferred as sound
• Vehicle slowing down


  • System is vehicle moving
  • When it slows down, kinetic transfers to thermal due to friction between wheels and brakes
• Kinetic energy


  E = 1/2 mv^2, where m is the mass in kilograms, kg, v is the speed, in metres per second, m/s and the kinetic energy, E in joules, J
• Potential energy in a spring

  E = 1/2 ke^2 where E is the total energy in joules, k is the spring constant in newtons per metre, and x is the extension in metres
• Gravitational Potential Energy


  • Ep is the gravitational potential energy, in Joules, J
  • g is the gravitational field strength (9.8ms), in newtons per kilogram, N/kg
  • h is the height in metres, m E=mgh
• Specific Heat Capacity


  The energy required to raise the temperature of 1kg of a substance by 1°C or 1K
• Calculating change in thermal energy


  • AE is the change in thermal energy, in joules, J
  • m is the mass, in kilograms, kg
  • c is the specific heat capacity, in joules per kilogram per degree Celsius, J/kg°C
  • AT is the temperature change, in degrees Celsius, °C. E=mc^T
• Power


  The rate at which energy is transferred or the rate at which work is done
• 1 joule per second is equal to 1 watt
• Two motors A and B


  The motor that can do the same work faster is more powerful
• Energy transfers


  • Energy can be transferred usefully, stored or dissipated but cannot be created or destroyed
  • In all system changes energy is dissipated, so that it is stored in less useful ways. This energy is often described as being 'wasted'
• Reducing energy waste


  • Lubrication (oil in a motor reduces friction)
  • Thermal insulation (double glazing reduces useful thermal energy lost)
  • Thermal conductivity (the higher the thermal conductivity, the more easily heat travels through the material)
• The rate of cooling is low if walls are thin and have low thermal conductivity