Physics Unit 2

Forces and their effects
1. Resultant forces
  1. Whenever two objects interact the forces they exert are equal and opposite
    1. hand pushing on table= table pushing back
  2. Lots of forces acting on one point
    1. replaced by single force doing everything together
      1. resultant force
        may cause a change in the state of object
2. Forces and motion
  1. Acceleration
    1. a=f/m
    2. m/s squared
    3. determined by resultant force (N) and mass (kg)
    4. the rate of change of velocity per unit of time
    5. a= v1-v2/t
      1. final velocity- initial velocity/ seconds taken
  2. velocity/time graphs
    1. Velocity = An objects speed in a certain direction
    2. the steeper the gradient the greater the acceleration
      1. a downward slope means constant decceleration
    3. a flat line = constant velocity
    4. distance = area of graph shape
    5. m/s
3. Forces and breaking
  1. when a car travels at a steady speed the driving force is balanced by resistive forces
    1. therefore the resultant force is 0
  2. when the breaks are applied
    1. work done by the friction between the brakes and the wheels reduce the kinetic energy of the vehicle
    2. the temperature of the breaks increase
  3. Stopping distances
    1. a drivers reaction time can be influenced by
      1. tiredness
      2. drugs
      3. alcohol
    2. a vehicles braking distance can be affected by
      1. adverse road/weather conditions
      2. poor condition of the vehicle
4. Forces and terminal velocity
  1. the faster an object falls the greater the friction
  2. Three stages of falling
    1. An object falls b/c gravity and weight. There is no air resistance. There is a resultant force downwards
      1. It gains speed, air resistance increases, there is a resultant force downwards.
        The objects weight is balanced by the air resistance, no resultant force, the object reaches terminal velocity
  3. w=m x g
    1. N=kg x N/kg
5. Forces and elasticity
  1. forces may change the shape of an object
  2. a force applied to an elastic object will result in the object stretching and storing elastic potential energy
  3. if an object returns to its original shape elastic potential energy is stored in the object when work is done on it
  4. f = k x e
The Kinetic energy of objects speeding up and slowing down
1. Forces and Energy
  1. work is done when a force causes an object to move through a distance
    1. Joules
    2. Energy is transferred when work is done
  2. W = F x d
  3. power = work done in a given time
    1. P = E/t
  4. the change in gravitational potential energy is what happens when something is raised
    1. Ep = m x g x h
  5. kinetic energy = 1/2 x mass x speed
    1. joules/kg/ meters per second
2. Momentum
  1. Momentum is the tendency of an object to carry on moving in the same direction
  2. Momentum = mass x velocity
  3. kg m/s
  4. momentum is conserved
    1. if nothing else acts on it the momentum stays the same through collisions and explosions
Currents in electrical circuits
1. Static electricity
  1. When insulating materials are rubbed against each other they become electrically charged
    1. Negatively charged electrons are rubbed of one material and onto the other
      1. equal amounts of opposite charge
    2. this only works for insulators
  2. when two charged objects are brought together they exert a force on each other
  3. electrical charges move better through other substances
    1. e.g. metal
2. Electrical circuits
  1. Electric current is a flow of charge
    1. The size of the electric current is the rate of flow of electric charge
      1. I = Q/T
        Current = charge/time
        amps = coulombs/ seconds
  2. potential difference is the work done per coulomb of charge that passes between two points in a circuit
    1. V = W/Q
      1. potential difference = work done/ charge in coulombs
  3. Current / potential difference graphs show that as current changes so does potential difference
    1. V= I x R
Using Mains Electricity safely and the power of electrical appliances
1. Household electricity
  1. direct current
    1. current that always passes in the same direction
      1. batteries, cells
  2. alternating current
    1. always changing direction
    2. mains electricity
      1. 50 hertz
      2. 230 V
  3. Electrical cables
    1. 2 or 3 inner wires
      1. copper core
    2. flexible plastic outer layer
  4. Structure of a plug
  5. If there is too much current
    1. it is stopped by the fuse/ circuit breaker/ live wire
      1. when there is too much current the fuse will melt and break the circuit
    2. a residual circuit breaker will detect a difference in the current between the live and neutral wires
      1. hey are faster than fuses
  6. appliances with metal cases are usually earthed
    1. the earth wire creates a safe route for the current to flow through
2. Current, charge and power
  1. When an electrical charge flows through a resistor, the resistor gets hot
    1. therefore energy is wasted
      1. filament bulbs waste energy
  2. The rate at which energy is transferred by an appliance is the power
    1. power = current x potential difference
      1. P = I x v
    2. energy transferred = potential difference x coulombs
      1. E = V x Q
    3. power = energy/time
      1. P=E/t

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	Criado por Apoorva Sriram quase 10 anos atrás