SP3 conservation of energy

• system


  a single object (eg. the air in a piston) or group of objects (eg. two colliding vehicles)
• what happens when energy is transferred in a closed system?

  there is no net charge to its total charge.
• different ways that energy can be transferred

  -mechanically- object moving due to a force acting on it, (eg. pushing, pulling, stretching or squashing)

  -electrically- a charge moving through a potential difference (eg. charges moving around a circuit)

  -by heating- energy transferred from a hotter object to a colder object (eg. heating a pan of water or a hob)

  -by radiation- energy transferred by waves (eg. energy from the sun reaching Earth by light
• conservation of energy principle 


  energy can be transferred usefully, stored or dissipated but can never be created or destroyed
• the thicker a building's wall and the lower the thermal conductivity...

  the slower the building will cool
• no devices are what?

  100% efficient
• Acceleration


  A measure of how quickly the velocity of something is changing. It can be positive if the object is speeding up or negative if it is slowing down.
• Balanced forces


  • When the forces in opposite directions on an object are the same size so that there is a zero resultant force.
• Resultant force


  The total force that results from two or more forces acting upon a single object. It is found by adding together the forces, taking into account their directions.
• Scalar quantity


  A quantity that has a magnitude (size) but not a direction. Examples include mass, distance, energy and speed.
• Speed


  How fast something is moving. Often measured in metres per second (m/s), miles per hour (mph) or kilometres per hour (km/h).
• Unbalanced forces


  • When the forces in opposite directions on an object do not cancel out, to there is a non-zero resultant force.
• Vector quantity


  A quantity that has both a size and a direction. Examples include force, velocity, displacement, momentum and acceleration.
• Velocity


  The speed of an object in a particular direction. Usually measured in metres per second (m/s).
• Centripetal force


  A force that causes objects to follow a circular path. The force acts towards the centre of the circle.
• Mass


  A measure of the amount of material there is in an object. The units are kilograms (kg).
• Weight


  The force pulling an object downwards. It depends upon the mass of the object and the gravitational field strength. The units are newtons (N).
• Gravitational field strength


  A measure of how strong the force of gravity is somewhere. It is the force on a 1 kilogram mass, so the units are newtons per kilogram (N/kg).
• Inertial mass


  The mass of an object found from the ratio of force divided by acceleration. The value is the same as the mass calculated from the weight of an object and gravitational field strength.
• Action-reaction forces


  • Pairs of forces on interacting objects. Action-reaction forces are always the same size, in opposite directions, and acting on different objects. They are not the same as balanced forces.
• Balanced forces


  • Forces acting on the same object. Balanced forces are always equal, in opposite directions, and always act on the same object. They do not have to be the same type of force. An object acted on by balanced forces will not change the way it is moving.
• Equilibrium


  When a situation is not changing because all the things affecting it balance out.
• Conservation of momentum


  The total momentum of moving objects before a collision is the same as the total momentum afterwards, as long as no external forces are acting.
• Momentum


  The mass of an object multiplied by its velocity. Momentum is a vector quantity, with units kilogram metres per second (kg m/s).
• Thinking distance


  The distance travelled by a vehicle while the driver reacts.
• Braking distance


  The distance travelled by a vehicle while the brakes are working to bring it to a halt.
• Stopping distance


  The distance in which a car stops, which is the sum of the thinking and braking distances.
• Reaction time


  The time taken to respond to a stimulus.
• Stimulus


  Something outside the body that can be detected by the body, such as a sight or sound.
• Response


  The way the body reacts to a stimulus.
• Crumple zone


  A vehicle safety device in which part of the vehicle is designed to crumple in a crash, reducing the force of the impact.
• Deceleration


  Slowing down - a negative acceleration