# Physics unit 3 revision

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• Physics - Unit 3 revision
• Motor effect and Fleming's left hand rule
• Magnetic fields
• The magnetic field lines come out of the north pole and go into the south.
• When you use Fleming's left hand rule the direction of the magnetic field is always from north to south.
• Fingers and meaning behind each finger
• The fist finger shows the direction of the conventional current which travels from + to -
• The second finger shows the direction of the magnetic field from the magents going from north to south.
• The thumb shows the direction of the force which is exerted on the wire.
• Important details
• The wire in the circuit must be insulated.
• The current flows out of the positive end and into the negative.
• Electrons flow out of the negative into the positive.
• Ways to change the direction the wire moves
• You can reverse the current - This will reverse the direction the wire moves
• You can flip the pole of the magnet - this will inverse the direction the wire moves
• You can move the magnet parallel to the wire - this will make it so that there is not interaction with the field and therefore there will be no resultant force.
• You can move the magnets closer together - this will make the wire move with more force
• You can use a stronger magnet - this will make the wire move with more force
• Moments and the principle of moments
• Equilibrium= balance / horizontal
• The sum of all the clockwise moments is equal to the sum of the anti clockwise monmets
• A turning effect is called a moment
• The equation is Moment (Nm) = Force (N) X Distance(m)
• The distance is always taken perpendicular to the pivot
• Ways to change the size of a moment
• The size of the moment is affected by the size of the force ( more force = bigger moment) and the distance away from the pivot ( the greater the distance the greater the moment)
• The overall direction that the object moves is called the resultant moment
• Hydraulics
• Pressure is equally distributed to the liquid / gas in all directions
• Liquids are virtually incompressibe
• The unit for pressure is pascals (pa)
• The force outputted by the hydraulic system is much greater than the force applied to it.
• The cylinder is filled with a liquid. The volume of the liquid doesn't change this means that the pressure to either side is increased and decreased.
• Pressure = force / area
• Force A = 1 area A = 1. Pressure A = 1/1 = 1.    Force B = ?  areaB=4      Pressure A = 1 therefore force B = 4 X 1 = 4.
• The slave piston is the piston that outputs the force ( the bigger one).
• The master piston is the one that inputs the force ( the smaller one)
• Centre of Mass
• The point at which the mass is thought to be most concentrated (still) is the centre of mass.
• If suspended the centre of mass will always be directly below the point of suspension
• If the centre of mass is inside the base of support the object will always stay balanced however if it lays outside the base of support then the object will topple over.
• It is in equilibrium when it is fixed  in its original position
• Pendulums
• The motion of a pendulum is oscillating
• The reason why it takes a long time to stop swining is because the amount of work done on the pendulum is only small
• A time period is how long it takes for the pendulum to reach the highest point on one side to the highest point on the otherside
• The unit for the number of oscillations is hertz (Hz)
• The frequency of oscillations is the number of time periods in 1 second
• The formula for time period is 1/frquency
• The oscillating amplitude is the distance from the fixed point to the highest point on either side