# Physics P3 GCSE AQA Using physics to make things work

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• Physics P3 GCSE AQA Using physics to make things work
• Centre of Mass
• The centre of mass of an object is a point in which the mass of the object may thought to be concentrated.
• To find the centre of mass in a irregular object you create a hole and dangle it from a piece of string, Draw a line straight down and repeat twice. Where the lines cross is the centre of mass
• When freely suspended, the centre of mass is directly below the point of suspension.
• The centre of mass of a symmetrical object is along the axis of symmetry.
• For a pendulum T=1/f (T is time in seconds and frequency is in hertz)
• The time period depends on the length of the pendulum.
• Moments
• The turning effect of a force is called a moment.
• Working out the size of a moment M=f*d (M is the force in newton metres Nm, f is force in newtons and d is the perpendicular distancefrom the line of action to the pivot in metres)
• If an object is not turning, the clockwise moment must equal the anticlockwise moment about any pivot.
• Levers act as force multiplyers.
• If the line of action of the weight of an object lies outside the base of the object then there will be a resultant moment and the object will topple.
• Hydraulics
• Liquids are incompressible and the pressure in a liquid is transmitted equally in all directions.
• When a force is exerted in one point of a liquid it will be transmitted to other point is tne liquid.
• The use of different cross sectional areas on the effort and load sideof a hydraulic system enables the system to be used as a force multiplyer.
• Pressure is given by the equation P=F/A (P is pressur in pascals, F is the force in newtons N and A is the cross-sectional area in metres squared m^2
• Circular motion
• When an object moves in a circle it continuously accelerates towards the centre of the circle
• The force causing the acceleration is called the centripetal force and is directed towards the centre of the circle.
• The centripetal force needed to make an object perform circular motion increases as:
• The mass of the object increases.
• The speed of the object increases.
• The radius of the circle decreases.