Resistance resitors stopping force breaking thinking acceleration velocity
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Unit P2 revision
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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
Light-dependent 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)
Speed =
distance/time
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