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# Leaving cert Physics

### Definitions - Mechanics

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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