Unit 1 Defenitions Flashcards
Scalar
Quantity with size only, e.g., distance
Vector
Quantity with size and direction, e.g., velocity
Friction
Force opposing motion
Newton’s First Law
If there is no resultant force an object it will :
-stay at rest
-or moves with uniform velocity
Newton’s Second Law
A resultant force will cause an object to accelerate
The acceleration is directly proportional to the size of the resultant force and acts in the same direction
Weight
Force due to gravity on an object
Mass
Amount of matter in a body
Acceleration of free fall, ‘g’
g = 10 m/s2.
The acceleration of an object allowed to fall freely from rest
Retardation
Negative acceleration or deceleration
Hooke’s law
The extension of a spring is directly proportional to the applied force, provided that the limit of proportionality is not exceeded
Moment of a force
Force applied multiplied by perpendicular distance from the pivot
Principle of Moments
When an object is in equilibrium the total clockwise moment about a point equals the total anticlockwise moment about the same point
Centre of Gravity
Point where object’s weight appears to act
Density
Mass per unit volume of material
Pressure
Force per unit cross-sectional area
Principle of Conservation of Energy
Energy cannot be created or destroyed, but can be changed from one form to another
The total amount of energy does not change
Renewable source
Resource which is naturally replenished within a human lifetime
Non-renewable source
Resource with a finite supply of energy which will run out some time
Work done
Force applied multiplied by distance moved
Kinetic energy
Energy possessed by a moving object
Gravitational potential energy
Energy possessed due to an objects position (height) in a gravitational field
Power
Rate at which work is done
Amount of work done (or energy transferred) in 1 second.
Efficiency
Fraction of input energy as useful output
Rutherford-Bohr model of atom
Small, dense, positive nucleus surrounded by shells of orbiting electrons
Atomic number Z
Total protons in an atom’s nucleus
Mass number A
Total protons and neutrons in an atom’s nucleus
Isotope
Different forms of the same element with the same atomic number (and same no. of protons) but different mass numbers (and no. of neutrons)
Radioactive
Unstable nucleus which randomly and spontaneously decays by emitting radiation (alpha, beta or gamma)
Background radiation
Radiation detected when no radioactive sources are present
Half Life
Time taken for the activity to fall to half its original value.
Alpha radiation
Particle identical to a helium nucleus; 2 protons and 2 neutrons
Charge +2
Mass 4u
Beta radiation
Fast electron emitted from unstable nucleus
Charge -1
Mass 1/1836 u
Gamma radiation
High energy electromagnetic radiation
Ionisation
Changing a neutral atom into a charged ion by removing an electron.
Fission
The splitting of a heavy nucleus (by absorption of a neutron) into 2 or more smaller nuclei, 2 or 3 neutrons and a large amount of energy
Fusion
The joining of 2 light nuclei to form a heavier nucleus, releasing a large amount of energy.
Conduction
Heat transfer through solids
- When heated the atoms vibrate faster and with a bigger amplitude (larger vibrations).
- They collide with neighbouring atoms and pass the heat energy along in the form of kinetic energy.
Conductor
A material which allows heat to pass through it easily (Metals are good conductors because they have free electrons)
- the free electrons gain kinetic energy.
- They move faster and transfer the energy through the metal by colliding into multiple atoms
This method is much quick than passing from atom to atom
Convection
Method of heat transfer in liquids and gas
This method involves the movement of particles
Convection current
Particles above heat source gain kinetic energy
- This causes them to move faster and further apart
- This part of liquid/gas becomes less dense and rises
- Cooler particles take the place of the particles which rose
Radiation
Heat travelling in self-supporting electromagnetic waves
