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What is resistance?
Resistance is a measure of how hard it is for a current to flow through a conductor  measured in ohms

the greater the resistance . . .
. . . the smaller the current

what is a variable resistor?
a resistor whose resistance can be altered

by altering resistance we can change ...
the current that flows through a component and the potential difference across a component

what is a fixed resistor
a resistor with only one value of resistance

Lightdependent resistors and thermistors are
components whose resistance depends on the surrounding external conditions

LDR restistance depends on light intensity its resistance decreases as light intensity
increases

thermistors resistance decreases as the temperature of the thermistor
increases

for most materials resistance increases in proportion to an increase in
temperature

Formula relating potential difference, current and resistance...
P.D (volts) = Current (amps) X Resistance (ohms)

A current potential difference graph shows how the current through a component varies with
the voltage across it

if we include a variable resistor in a practical circuit we can get
a range of current and voltage readings which can be used to plot a graph

explain diodes
current only flows in one direction. a very small current flows until a trigger voltage is reached after which point current rises rapidly with increase in potential difference (low resistance)

When an electric current passes through a resistor there is an energy transfer and the resistor becomes heated why?
the moving electrons collide with ions in the lattice of the metal resistor. as a result of these collisions energy is transferred from electrical to thermal

power is electrical energy transferred in one second. formula...
Electrical power (watt) = current (amperes) X P.D (volts)

energy transfer formula
Energy transferred (joules) = current (amperes) X PD (volts) X time (seconds)


The slope of a distance time graph represents the speed of an object. The steeper the gradient the greater the
speed

Displacement is
distance travelled in a stated direction  it is a vector quantity

what is a vector quantity?
has both size and a direction

velocity =
speed in a stated direction. Like displacement it is a vector quantity

acceleration=
the rate at which its velocity increases (m/s2)

acceleration formula=
Change in velocity (m/s)/Time taken for change (s)

The slope of a velocity time graph represents the acceleration of an object. The steeper the gradient the greater the
acceleration

force is measured in
newtons (N) it is a vector quantity as it has both a size and a direction

Object A exerts a force on object B this is called
an action force

object B will exert a force of equal size and opposite direction on object A this is called
a reaction force

when forces are balanced we say they are
in equilibrium

the combined effect of forces is called
the resultant force and this force affects any subsequent motion on the object

acceleration happens when
the driving force is greater than the resistive force

decceleration happens when
the resistive forec is greater than the driving force

constant speed happens when
the driving force is equal to the resistive force

To calculate resultant force you can draw a
free body diagram

Force(N)=
Mass (kg) X acceleration (m/s2)

Weight is
a measure of the force exerted on a masss due to the pull of gravity , as it is a force the units are in newtons (N)

weight formula=
Mass (kg) X Gravitational field strength (N/kg)

a falling object accelerates until the resultant forces are zero. This is called
terminal velocity

Stopping distance=
thinking distance + breaking distance

Factors affecting stopping distance are...
the speed of the vehicle, the mass of the vehicle, the conditions of vehicle/terrain and the drivers reaction time

