11.2 - Forces Flashcards
What is equilibrium?
No result force, so no change or movement
action and reaction forces equal / opposite
What is weight?
mass x grav potential energy
m x 9.81 Newtons
Moon grav pot energy?
1.622 m/s2
What is density?
Mass per unit volume
p (rho) = m / V kg/m3
Density of materials?
Concrete - 2400
Ali - 2700 (rel. 2.7)
Brass - 8500 kg/m3
Properties of force?
Size (magnitude)
Direction of action
Point of application
What is pressure?
Stress, a force applied to an object, eg floor, wall
P = F / A
What are moments?
Force that produces a turning effect
M = F x distance (force from turning point) Nm
What are the units of temp?
C, F and K
Celsius to Fahrenheit?
F = (C x 9/5) + 32
Celsius to Kelvin?
K = C +273
What is thermal expansion?
When heated, gases, liquids and solids will expand
change in length = coeff (alpha) x length x (temp rise)
Coefficient of linear expansions (alpha)?
iron - 0.000010
Steel - 0.000012
Ali - 0.000024
Modes of heat transfer?
Conduction (touch)
Convection (radiator)
Radiation (empty space, we absorb rad via the sun)
What is specific heat capacity?
The heat required to raise the temperature of the unit mass of a given substance by a given amount (usually one degree)
Thermal energy equation?
Q = mass x SHC x change in temp Joules
SHC of materials?
Copper - 380 J/kg.K
Iron - 450
Steel - 490
Coefficient of friction equation?
mu = Friction / Normal force mu = Friction / mass x grav pot energy
Coefficient of friction examples?
Rubber on concrete - static = 1, kinetic = 0.8
Teflon on Teflon - static = 0.04, kinetic = 0.04
Types of bonding?
Ionic (electrovalent)
Covalent
Metallic
Series resistors?
Total R = R1 + R2 …
Parallel resistors?
1/RT = 1/R1 = 1/R2 …
Earth’s magnetic poles?
North is actually a magnetic south pole
South is magnetic north
Flow of magnetism?
North to South
How to store magnets?
In pairs, using soft iron keepers
Concentric circles?
magnetic flow around a conductor, strongest at the conductor itself
Right hand rule?
Hand is conductor
thumb is current flow
fingers show direction of magnetic flux
Current flow symbols?
dot = flow towards you cross = away from you
How to strengthen magnetic field?
Shape a conductor into a loop (concentrated mag flux in centres) or coiled form to create a solenoid (resembles magnet), having a soft iron (ferromagnetic) core
What are relays?
Electrochemical devices consisting of a coil of wire wound on a ferromagnetic core fitted with a moving armature
linked to a set of switch contacts that make or break when the device is actuated
How does a relay work?
when sufficient current is applied, the resulting mag field will magnetise the core, pulling the arm towards the core, opening or closing the relays electrical contacts
