IG物理

关于IG物理的思维导图，汇总了turning effects、force and motion、electrical quantities、magnetism知识。

物理暑假作业

• turning effects
  • the moment of a forcce
    • a moment(力矩) is a turning effect caused by a force
      • the bigger the force, the larger the moment
      • the moment of a force is bigger if it acts further from the pivot
      • the moment of a force is greatest if it acts at 90° to the object it acts on
    • turning effect: when a force causes an object to rotate or would make the object rotate if there were no resistive forces
    • pivot(轴心): the fixed point about whitch a lever turns, also known as the fulcrum
    • equilibrium: when no net force and no net moment act on a body
      • the forces on it must be balanced
      • the turning effects of the forces on it must also be balanced
  • calculating moments
    • moment(Nm)=force(N)*perpendicular distance from pivot(m) moment=F*⊥d
  • stability and centre of gravity
    • stable: an object that is unlikely to topple over, often because it has a low center of gravity and a wide base
    • unstable: an object that is likely to topple over, often because it has a high centre of gravity and a narrow base
    • centre of gravity: all the mass of an object could be located here and object would behave the same
    • find the centre of gravity
      • for regular figures, the center of gravity is the geometric center of them
      • for irregular figures, Suspension method is most commonly used
        • step1: find a string, find a point on the object, hang with the rope, wait for the object to rest, connect a vertical line through the suspension point
        • step2: Find a little bit of suspension outside of that vertical line.
        • step3: The intersection of two vertical lines is the center of gravity of the irregular object.
• force and motion
  • mass, weight and gravity
    • weight=mass*acceleration of free fall W=mg
    • gravitational field strength=weight/mass g=W/m
    • gravity: the force that exists bwtween any two objects with mass
    • acceleration of free fall: the acceleration of an object falling freely under gravity
    • acceleration due to gravity: the acceleration of an object falling freely under gravity
    • gravitational field strength: the gravitational force exerted per unit mass placed at that point
  • falling and turning
    • terminal velocity: the greatest speed reached by an object when moving through a fluid
    • a bigger force is needed if
      • the object's mass is bigger(and speed and radius stay the same)
      • the object's speed is bigger(and speed and radius stay the same)
      • the radius of the circle is smaller(and speed and mass stay the same)
  • force, mass and acceleration
    • force(N)=mass(Kg)*acceleration(m/s^2) F=ma
  • momentum(动量)
    • momentum is the basic quantity of motion
    • momentum(kg m/s)=mass(kg)*velocity(m/s) P=mv
    • the effect of a force F depends on
      • how big the force is
      • the time interval Δt it acts for
    • impulse(冲量): the change in an object's momentum , Δp, or the force acting on an object multiplied by the time for whitch the force acts
      • impulse=force*time for whitch the force acts I=FΔt=Δ(mv)
    • resultant force(合力): the single force that has same effect on a body as two or more forces
      • resultant force=change in momentum/unit of time F=Δp/Δt
  • more about scalrs and vectors
    • scalrs and vectors
      • scalrs have magnitude(size) only and no direction, but vectors have both direction and magnitude
    • rules for vector addtion
      • draw arrows end-to-end, so that the end of one is the start of the next
      • choose a scale that gives a large triangle
      • join the start of the first arrow to the end of the last arrow to find the resultant force
• electrical quantities
  • current in electric circuits
    • current: the rate at whitch electric charge passes a point in a circuit
    • cell: a device that provides an electromotive force(emf电压/电势差)in a circuit by means of a chemical reaction
    • battery: two or more electrical cells connected together in series
    • direct current(dc)直流电: electric current that flows in the same direction all the time
    • alternating current(ac)交流电: electric current that changes direction
    • conductors(导体) and insulators(绝缘体)
      • conductor: a material that allows an electric current to flow through it
      • insulator: a materiall that not allows an electric current to flow through it
      • charge: carried around a circuit by the ccurrent, negative charge is carried by electrons
      • most metals, including copper, silver, goldand steel are goods conductors
      • polymers聚合物(eg: perspex塑料 and polythene聚乙烯)are goods insulators
    • measureing electric current
      • galvanometer(电流表): a meter for measuring tiny electric current
      • ammeter(电流表): a meter for measuring electric current
      • amphere(安培): the SI unit of electric current(A)
    • current and charge
      • current(A)=charge(C)/time(S) I=Q/t
  • voltage in electric circuits
    • voltage电压: the energy tranferred or work done per unit charge, it can be imagined as the push of a battery or power supply in a circuit
    • potential different电势差(pd): the work done by the a unit of charge passing through an electrical component, another name for the voltage between two points
    • electromotive force电动势(emf): the electrical work done by a source in moving a unit of charge around a circuit, the voltage across the terminals of a source
      • combining emfs: E=E1+E2+......
    • work done by the charge/charge W/Q
    • volts(V): the SI unit of voltage(pd or emf), 1V=1C/S
    • voltmeter: a meter for measuring the pd between two point
  • electrical resistance
    • resistance电阻: a measure of how difficult it is for an electric current to flow through a device or a component in a circuit, it is the pd across a component divided by the cuurent through it
      • resistance(Ω)=potential differnence(V)/current(A) R=V/I
    • Ohm(Ω): the SI unit of electrical resistance, 1Ω=1V/A
    • resistance and thickness
      • the longer a wire, the greater its resistance
      • the greater the diameter of a wire, the less its resistance
  • electrical energy, wore and power
    • electrical power
      • electrical power: power=current*pd(p=VI)
    • calculating energy
      • energy transferred=current*pd*time E=VIt
• magnetism
  • permanent magnets
    • bar magnets: a rectangular-shaped permanent magnet with a north pole and south pole
    • when two magnets are brought close together: like poles repel, unlike poles attarct
    • magnetised磁化: when a magnetic material has been made magnetic
    • demagnetised消磁: when a magnetic material has not been made magnetic
    • induced magnetism诱导磁性: when a magnetic material is only magnetised when placed in a magnetic field
    • permanent magnet永磁体: magnetised magnetic material that produces its own magnetic field that does not get weaker with time
    • hard material硬磁材料: a material that, once magnetised, is difficult to demagnetise
    • soft material软磁材料: a material that, once magnetised, is easy to demagnetise
  • magnetic field
    • two things about the field
      • direction: the direction of a magnetic field line at any point is the direction of force on the north pole of a magnet at that point. We use a convention that says that field lines come out from north poles and go in to south poles
      • strength: lines that are close togther indicate a strong field