physics Flashcards
which one is highest frequency on the em waves ?
gamma rays
mass (kg) and weight (N) differences
MASS
- measured by beam balance or electronic balance
- remains CONSTANT
WEIGHT
- measured by extension spring balance or compression springs balance
- varies
w=mg
define inertia
the inertia of an object referred to the reluctance of the object to start moving if it is stationary
define gravitational field strength
is a region in which a mass experienced a force due to gravity attraction
w=mg
define density
the density of a substance is defined as it’s mass per unit volume
m =d/v
more dense , sinks
less dense , rise
define MOMENTS OF A FORCE
defined as the product of the force and the perpendicular distance from the pivot to the line of action of the force
moment (Nm) = f (N) x d (m)
define PRINCIPLE OF MOMENTS
when a body is in equilibrium, the sum of clockwise moments about a pivot is equal to the sum of anti clockwise moments about a pivot
sum of cw = sum of acw
define centre of gravity
the c.g of an object is defined as the point through which the whole weight appears to act
stability
neutral:
- does not topple
- remains at same lvl
- c.g remains
stable:
- does not topple
- rises and fall back
- c.g rises
unstable:
- topples
- falls further
- c.g gets lower
factors affecting stability
position of c.g
- lower c.g , more stable it is
base area
- large area , more stable it is
principal of conservation of energy
energy can neither be created or destroyed. It can only be converted or transferred from one form to another
kinetic particle theory
SOLID (arrangement) - closely packed together in an orderly arrangement (movement) -vibrate about in their fixed positions
LIQUID
(arrangement)
- closely packed together but not in an orderly arrangement
(movement)
-slide and roll over each other , moving freely throughout the liquid
GAS (arrangement) - far apart and not in an orderly arrangement (movement) - moving freely at high speeds
summary of thermal energy
conduction
- molecular vibration
- free electrons (metals only)
convection
- difference in density
radiation
- colour and texture
- surface area
- surface temp
conduction
occurs in solid liquid and gas , cannot occur in vacuum
molecular vibration
- molecules at the hot side vibrate vigorously and jostle their surrounding molecules, making them vibrate as well
- kinetic energy of the vibrating molecules at the hot side gets transferred to their neighbours
free electron diffusion (metals only)
- when metal rod is heated , free electrons move at high speeds, having more kinetic energy.
- these fast electrons spread into the cooler parts and then transfer their kinetic energy to one another
convection
only occurs in liquid and gases
eg of a description,
- water at the bottom heated , expands , less dense , starts to rise
- cooler regions at the upper part being denser , now sinks
- movement of the fluid due to a difference in density sets up a convection current
