P1 Energy Conservation & Dissipation

• Work done = force x distance moved by object
• Where is chemical energy found?

  Food, fuels, batteries
• What does kinetic energy describe?


  The energy an object has moving
• What does gravitational potential energy describe?

  The energy an object has due to it's position from ground
• What does elastic potential energy describe?


  The energy in a springy object to squish or squash
• What does thermal energy describe?

  The enrgy a substance has due to it's temperature
• Energy is ----------- and can be presented in a ---- diagram

  Transferred / dissipated

  Flow
• Where is the maximum amount of gravitational potential energy in a pendulum and why?


  As it moves away from the centre leftwards and rightwards as the kinetic energy decreases
• Where is the maximum amount of kinetic energy in a pendulum?

  When the bulb is moving towards the centre as the force from an increase of gravitational energy causes the speed of movement to increase
• What is a closed system?

  Matter cannot enter/leave but energy can be exchanged within the closed surroundings. e.g. a sealed jar, no matter can enter like air but the gases within the sealed jar can interact with each other.
• Conservation of energy


  Energy cannot be created or destroyed
• Name the first energy transfer of a bungee jumper:

  When the rope is slack, the energy of gravitational potential energy transfers to kinetic energy as the bungee cord accelerates towards the ground due to gravity
• Name the second energy transfer of a bungee jumper:

  As the tight ropens, the force of the rope reduces the speed of the jumper. The kinetic energy decreases and the elastic potential energy increases as the rope stretches. Eventually the jumper stops and all that kinetic energy has transferred into elastic potential energy.
• When testing a bungee jump cord what is one safety precaution?

  Protect feet from falling objects by keeping a few cm away from the desk
• Name the third energy transfer of a bungee jumper:

  Reaching the bottom, the jumper recoils and jumps back up. As the jumper rises, the energy in the elastic potential decreases and the kinetic energy increases
• What is the waste energy in the bungee jump?

  Thermal energy transferred to surroundings from the tightening of rope
• energy transferred=work done
• Mass (Kg) x gravitational field strength (N/Kg) x change of height (m)
• Change in gravitational potential energy=


  Mass (Kg) x gravitational field strength (N/Kg) x change of vertical height (m)
• What is Hooke's Law?


  F= k e As the force increases, so does the extension, they are in relation to each other
• Elastic potential energy (J)=


  0.5 x spring constant (N/m) x extension squared (m squared)
• Kinetic energy (J)=


  0.5 x mass (kg) x speed squared (m/s squared)
• Name one way wasted energy is caused?

  Friction
• How can you prevent friction (wasted energy)in a machine to make more efficient

  -lubrication

  -streamline shapes

  -tighten loose parts (reduce noise)
• calculation for efficiency=


  useful output energy transfer (J) / total input energy (J)
• calculation for wasted power =

  total power in-useful power out
• Power calculation (W)


  energy transferred to appliance (J) / time taken (s)