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Physics Crib Sheet 10 - Laws, Theories and Principles

- A hypothesis is just an idea, it could be correct, incomplete or wrong
- When scientists agree that a hypothesis is correct, they will label it as a theory
- When a theory stands the test of time and it still works flawlessly, the scientists will call it a law
- Science often advances when the "laws" are proved wrong.

Big Bang Theory | The Universe and everything it contains was formed during a massive explosion which took place about 14,000,000,000 years ago. |

Archimedes Principle | When a body is partly or wholly submerged in a fluid the upthrust it experiences is equal to the weight of fluid displaced. |

Bernoulli’s Principle | Increasing the speed of a flowing fluid will decrease the fluid’s pressure. Decreasing speed will increase pressure. |

Boyle’s Law | The pressure of a fixed mass of gas will be inversely proportional to its volume, provided the temperature remains constant. |

Charles’ Law | The volume of a fixed mass of gas is proportional to its temperature, provided the pressure remains constant. (Temperature must be measured in Kelvin because the other scales do not start from zero.) |

Conservation of Charge | Electrical charge cannot be created or destroyed. (But it can be moved from place to place.) |

Conservation of Energy | Energy cannot be created or destroyed, you can only change it from one type of energy to another. (Mass, Potential Energy, Chemical Energy and Kinetic Energy are some types of energy.) |

Conservation of Momentum | If two (or more) objects collide, the total momentum of all the objects will not change. (the total momentum will not change unless an external force is applied.) |

Faraday’s Law | The voltage produced in a conductor is directly proportional to the speed that the conductor travels through a magnetic field. (Law applies to electromagnetic generators) |

Fleming’s Left Hand Rule (for Motors) | Position the thumb, first finger and second finger of your left hand so they point at 90° to each other. If your First finger points in the direction of the Field and your seCond finger points in the direction of the Current then your thuMb will be pointing in the direction of Motion. (To help remember Left Hand rule for motors and Right Hand rule for generators, think of the misspelling geneRIGHTer.) |

Fleming’s Right Hand Rule (for Generators) | Position the thumb, first finger and second finger of your left hand so they point at 90° to each other. If your First finger points in the direction of the Field and your seCond finger points in the direction of the Current then your thuMb will be pointing in the direction of Motion. (To help remember Left Hand rule for motors and Right Hand rule for generators, think of the misspelling geneRIGHTer.) |

Gas Laws | These are listed under Charles’ Law, Boyle’s Law and the Pressure Law. The three laws can be combined and summarised by the equation ^{pressure x volume}/_{temperature} is constant. |

Heisenberg’s Uncertainty Principle | The accuracy that the speed of a small object can be measured is inversely proportional to how accurately its position can be determined. |

Hooke’s Law | The extension of a spring is proportional to the applied force. (Unless the elastic limit is exceeded.) |

Hubble’s Law of Cosmic Expansion | The velocity at which two galaxies move apart is proportional to the distance that separates them. |

Floatation Rule | When a body floats in a fluid, it will displace its own weight. |

Kepler’s First Law of Planetary Motion | Planets orbit a sun in an elipse. The sun will be one focus of this elipse. |

Kepler’s Second Law of Planetary Motion | A line joining an orbiting planet to it’s sun will always sweep equal areas within fixed time periods. |

Kepler’s Third Law of Planetary Motion | The square of a planet’s orbital period is proportional to the cube of the orbit’s semi-major axis |

Lenz’s Law | The direction of an induced current will always oppose the change that created it. (Law applies to electromagnetic generators) |

Newton’s Law of Gravity (Newton’s Universal Law) | The gravitation force between two objects is proportional to the product of their masses and inversely proportional to the square of the didyance between them. {F = ^{(G x m1 x m2)} / _{r2}}G=Gravitational Constant, m1 m2 = mass, r=distance apart) |

Newton’s First Law of Motion | The velocity of a body will remain constant unless a force is applied to it. |

Newton’s Second Law of Motion | The acceleration of a body is directly proportional to the applied force. |

Newton’s Third Law of Motion | To every action there is an equal but opposite reaction. (If object A applies a force on object B, then object B must all apply an equal but opposite force on object A.) |

Ohm’s Law | The current through a metallic conductor is directly proportional to the voltage applied. (Provided everything else remains unchanged.) |

Pressure Law | The pressure of a fixed mass of gas is directly proportional to temperature, provided the volume is kept constant. (Temperature must be measured in Kelvin because the other scales do not start from zero.) |

Theory of General Relativity | Gravity works by distorting the space-time continuum |

First Law of Thermodynamics | When heat is added to a system, some of the energy is used to do the work and all the rest is used to increase the internal energy of the system. |

Second Law of Thermodynamics | You cannot move heat from a colder object to a hotter one without using energy |

Third Law of Thermodynamics | It is impossible to achieve the temperature known as Absolute Zero. |

Wave particle Duality Theory | Small particles can behave as waves (e.g. the electron is a particle with mass but it is also a wave with a frequency and wavelength.) |

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