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# Physics mechanics

### mechanics definitions

Question | Answer |
---|---|

What is displacement s of an object? | Is the resultant distance moved in a given direction |

Define a scalar quantitiy? | Has magnitude only |

Define a vector quantity? | Has magnitude and direction |

how can you find the resultant of two vectors? | it can be found using a triangle, parallelogram or rectangle to represent them |

What are the components of a vector inclined at and angle of ? to the horizontal? | horizontal component = V cos ? Vertical component = V sin ? |

How do you find the average speed V of an object? | Total distance/time |

How do you find the instantaneous speed of an object? | the rate of change of distance x: V = ^x/^t |

What is velocity? | the rate of change of displacement S: a = ^s/^t |

What is acceleration? | the rate of change of velocity V: a = ^v/^t |

What does the gradient of a displacement-time graph represent? | velocity: v = ^s/^t |

What does the gradient of a velocity-time graph represent? | acceleration: a = ^v/^t |

What does the area under a velocity-time graph represent? | displacement |

What equation do you use for motion at a constant velocity? | v = x/t |

What are the equations that are used for motion at constant acceleration? | V = u + at S = ut + 1/2at^2 S = 1/2(u+v)t V^2 = u^2 + 2as |

How can you describe the horizontal and vertical velocities of a projectile? | It moves with constant horizontal velocity and a vertical velocity changing due to acceleration due to free fall |

What is the equation that links resultant force on an object to it's mass and acceleration? | F = ma |

Define the newton. | A force that gives a mass of 1 kg an acceleration of 1 m/s^2 |

What is the equation for weight? | Weight = mass x gravitational field strength |

Why can't F = ma be used at high speeds? | Mass increases with energy |

What is viscous drag? | Objects moving through air or liquids experience air resistance or viscous drag |

What factors does the magnitude of the viscous drag depend on? | The medium, the size of the object and the speed of the object |

What happens to the viscous drag force when speeds increase? | It increases with speed |

For an object falling through air explain how an object will reach terminal velocity. | For a falling object in air under gravity, the drag increases until it equals the weight. The resultant force and acceleration are then zero so the object continues at a constant. |

What is the center of gravity of an object? | The point where it's whole weight may be considered to act |

Define the moment of a force | Force x Perpendicular distance from force line to point |

What is a couple? | A pair of forces that are equal in magnitude but act in opposite directions, producing rotation. |

What is the torque of a couple? | One force x perpendicular distance between them |

What is the principle of moments? | For a body in equilibrium, sum of clockwise moments = sum of anticlockwise moments |

What is thinking distance? | Distance traveled while the driver reacts Thinking distance = reaction time x speed of vehicle |

What is braking distance? | Distance traveled after brake has been applied. Depends on mass of vehicle and the efficiency of the brakes, and is proportional to the square of the speed |

How do air bags, crumple zones reduce the impact force on a passenger? | increase the time and distance taken to come to rest so therefore reduce impact forces |

How dopes GPS work? | Global Positioning Systems use the transliteration technique |

What is work done? | Force x Distance moved in direction of the force |

Define the joule? | The energy transferred when a force of 1N moves a distance of 1m in the direction of the force |

What is the conservation of energy? | Energy cannot be created or destroyed, only changed from one to another |

What is kinetic energy? | It is equal to the work done in bringing a moving object to rest. 1/2mv^2 |

What is gravitational potential energy? | mg^h |

Define power. | The rate of working. work done/time taken |

Define a watt. | It is developed if 1 joule of energy is transferred in a time of 1 second |

Define efficiency. | Useful energy output / energy input x 100% |

Define density. | mass per unit volume. m/V Density of water = 1g/cm^3 = 1000kg/m^3 |

Define pressure. | Force per unit area. F/A Standard atmospheric pressure = 100000N/m^2 = 100kPa |

Describe Hooke's law. | For a spring or material which is stretched up to it's elastic limit, the extension is proportional to the tension |

Define the spring constant. | Force per unit extension. F/^x |

Describe elastic deformation. | Energy is lost and the material is permanently deformed |

What does the area under a force-extension graph represent? | The work done done in stretching a spring |

White down 2 equations for elastic potential energy. | 1/2F^x = 1/2k^x^2 |

Define tensile stress. | Force per unit cross-sectional area. F/A |

Define tensile strain. | Extension per unit length. ^x/L |

Define the young modulus. | Stress/Strain. Young modulus of steel is 2 x 10^11 Pa |

Define ultimate tensile strength. | The stress at which a material breaks |