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Leaving cert Physics
Definitions - Mechanics
| Question | Answer |
|---|---|
| Vector | A quantity which has both magnitude and direction. |
| Scalar | A quantity which has magnitude only. |
| Distance | A measure of the separation between two points. |
| Displacement | The separation between two points in a given direction. |
| Speed | The distance traveled per unit time. |
| Velocity | The rate of change of displacement. |
| Acceleration | The rate of change of velocity. |
| Equations of motion | v = u + at, s = ut +1/2at², v² = u² + 2as |
| Momentum | The product of the mass and velocity of a body p = mv |
| The principle of the conservation of momentum | In any closed system of colliding bodies, the total momentum remains constant |
| Force | That which changes or tends to change the velocity of an object |
| Newton | A force of 1 N gives an acceleration of 1m/s-² to a mass of 1kg |
| Weight | The force with which a force is attracted to a planet W = mg |
| Friction | The force that opposes motion between two surfaces in contact |
| Newtons 1st Law of motion | A body remains at rest or in uniform motion unless acted upon by a resultant force. |
| Newtons 2nd Law of motion | The rate of change of an objects momentum is directly proportional to the force that caused it, and takes place in the direction of that force. F = ma |
| Newtons 3rd Law of motion | For every action there is an equal and opposite reaction. |
| Work | When a force causes a body to be displaced W =Fd |
| Energy | The ability to do work |
| Potential energy | The energy that a body has due to it's position or state P.E = mgh |
| Kinetic energy | The energy a body has due to it's motion K.E = 1/2mv² |
| 1 Joule | The work done when a force of 1N displaces an object by 1m |
| The principle of conservation of energy | Energy can neither be created or destroyed , only converted from one form to another |
| Power | The rate at which work is done or energy is converted P = W/t |
| 1 Watt | 1 watt of power is equal to doing 1 joule of work per second |
| A renewable source of energy | an energy source that will not be exhausted e.g, wind , tidal , solar |
| The efficiency of a machine | The energy output as a percentage of energy input |
| Lever | Any rigid body that is free to move around a fixed point called a fulcrum |
| The centre of gravity | The point at which the weight of the object appears to act |
| The moment of a force (Torque) | The force applied multiplied by the perpendicular distance from the fulcrum M = Fd |
| Conditions for equilibrium | 1. The vector sum of the forces in any direction must be zero. 2. The sum of the moments about any point must be zero. |
| A Couple | Two parallel forces that act in opposite directions. The moment of a couple is the magnitude of one force multiplied by the perpendicular distance between them |
| Hooke's law | The extension of an elastic body is directly proportional to the force extending it |
| Simple Harmonic Motion (SHM) | Motion where an objects acceleration is directly proprtional to it's displacement from a mean position and is always directed towards it |
| Newton's law of universal gravitation | The force between two bodies is directly proportional to the product of their masses. And inversely proportional to the square of the distance between them |
| Centripetal Force | The force acting towards a centre of a body moving in a circular path |
| Angular Velocity | The angle, in radians, swept out per second |
| Periodic time | The time taken to complete one revolution |
| Kepler's 3rd Law | The square of the periodic time of a satellite is directly proportional to the cube of it's radius of orbit and inversely proportional to the mass of the planet it orbits |
| Density | The mass per unit volume of a substance p = m/v |
| Pressure | The force per unit area P = F/A |
| Archimedes' principle | When a body is partially or fully immersed in a fluid, it experiences an upthrust which is equal to the weight of the liquid displaced |
| Law of flotation | A floating body displaces it's own weight of fluid |
| Boyle's Law | For a fixed mass of gas at constant temperature, its volume is inversely proportional to it's pressure |
Created by:
neilkelly
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