Physics two

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  • Created on: 19-05-16 21:24
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  • Physics two
    • Forces
      • Laws
        • If an object is not moving and it has no force on it, it will be stationary
        • The force pushing a grounded object up is called the normal
        • When a force acts on a stationary object the object moves in the direction of the force
        • If no force is acting on a moving object it doesnt stop.
      • Acceleration
        • Acceleration is the rate of change in velocity. This means an object only accelerates if:
          • Its speed changes
          • Its direction changes
      • Terminal velocity
        • No motion doesnt mean no force
        • Constant speed means no resultant speed
        • Increasing velocity does not mean increasing the force
        • Increasing acceleration does mean greater resultant force on an object
        • For every action there is an equal and oposite reaction
    • Energy
      • Momentum
        • All moving objects have momentum
        • Momentum is the measure of how difficult it is to stop a moving object
        • It is measured kgm/s
        • Conservation of momentum
          • Momentum before the colision is equal to the momentum after the collision.
      • Impulse
        • The quantity 'force x time' is known as an impulse
        • The impulse measures the effect of the force
        • impulse is measured in newton seconds (Ns or kgm/s)
    • Circuits
      • Static electricity
        • Charging occurs when electrons are transferred from one material to another.
          • Friction can transfer electrons
        • Like charges always repel each other and unlike always attract each other
        • When two electrically charged objects are brought together they exel a force on one another
      • Electrodynamics
        • The basic unit of eletrical charge is coulamoh (C)
        • Current is easured in amps (A)
          • Amps are meausred by an ammeter
        • Metals are good conductors of electricity because they have free electrons that can move easily from atom to atom, so that the current flows
      • Resistance
        • A resistor is a componant which is made to have a certain resistance
          • It helps regulate current flow
        • Ohm's law: the current throught a metal wire is directly propertional to the p.d across it (providing the temperature remains constant
          • The resistance of the wire is the ratio of the p.d applied across it, to the current passing through it.
        • It is measured in ohnus
      • Current
        • Direct current (DC)
          • Flows in one direction
          • Bateries and cells supply a DC current
        • Alternating current (AC)
          • The current changes direction due to a magnet turning through a wire at the power station
          • Mains electricity has a frequency of 50Hz of the current alternates 50 times a second
      • Wires
        • The neutral wire of a plug stays at a potential close to zero with respect to the earth
        • The live wire alternates between a positive and negative potential with respect to the neutral wire
        • If a fault occurs where the live wire connects to the case, the earth wire allows the large current to flow through the earth wire to the ground
      • Fuses
        • If the appliance develops a fault, the current may become too high. to avoid further damage we have a fuse
        • A fuse  has a thin piece of wire inside it, which is the weakest link in the circuit.
          • If too much current flows through the fuse the wire mealts, breaking the circuit.
          • It is connected with the live wire

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