Physics 2

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Physics 2
2012-12-06 14:20:43
Resistance resitors stopping force breaking thinking acceleration velocity

Unit P2 revision
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  1. What is resistance?
    Resistance is a measure of how hard it is for a current to flow through a conductor - measured in ohms
  2. the greater the resistance . . .
    . . . the smaller the current
  3. what is a variable resistor?
    a resistor whose resistance can be altered
  4. by altering resistance we can change ...
    the current that flows through a component and the potential difference across a component
  5. what is a fixed resistor
    a resistor with only one value of resistance
  6. Light-dependent resistors and thermistors are
    components whose resistance depends on the surrounding external conditions
  7. LDR restistance depends on light intensity its resistance decreases as light intensity
  8. thermistors resistance decreases as the temperature of the thermistor
  9. for most materials resistance increases in proportion to an increase in
  10. Formula relating potential difference, current and resistance...
    P.D (volts) = Current (amps) X Resistance (ohms)
  11. A current potential difference graph shows how the current through a component varies with
    the voltage across it
  12. 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
  13. 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)
  14. 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
  15. power is electrical energy transferred in one second. formula...
    Electrical power (watt) = current (amperes) X P.D (volts)
  16. energy transfer formula
    Energy transferred (joules) = current (amperes) X PD (volts) X time (seconds)
  17. Speed =
  18. The slope of a distance time graph represents the speed of an object. The steeper the gradient the greater the
  19. Displacement is
    distance travelled in a stated direction - it is a vector quantity
  20. what is a vector quantity?
    has both size and a direction
  21. velocity =
    speed in a stated direction. Like displacement it is a vector quantity
  22. acceleration=
    the rate at which its velocity increases (m/s2)
  23. acceleration formula=
    Change in velocity (m/s)/Time taken for change (s)
  24. The slope of a velocity time graph represents the acceleration of an object. The steeper the gradient the greater the
  25. force is measured in
    newtons (N) it is a vector quantity as it has both a size and a direction
  26. Object A exerts a force on object B this is called
    an action force
  27. object B will exert a force of equal size and opposite direction on object A this is called
    a reaction force
  28. when forces are balanced we say they are
    in equilibrium
  29. the combined effect of forces is called
    the resultant force and this force affects any subsequent motion on the object
  30. acceleration happens when
    the driving force is greater than the resistive force
  31. decceleration happens when
    the resistive forec is greater than the driving force
  32. constant speed happens when
    the driving force is equal to the resistive force
  33. To calculate resultant force you can draw a
    free body diagram
  34. Force(N)=
    Mass (kg) X acceleration (m/s2)
  35. 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)
  36. weight formula=
    Mass (kg) X Gravitational field strength (N/kg)
  37. a falling object accelerates until the resultant forces are zero. This is called
    terminal velocity
  38. Stopping distance=
    thinking distance + breaking distance
  39. 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