AQA Physics 3 - Using Physics to Make Things Work

Moments
1. The turning effect of a force
  1. Size of the moment is given by
    1. M= f x d
      1. D(istance) from the pivot - m
2. To increase the moment:
  1. - Increase the distance to the pivot
    1. - Increase the force
3. Levers
  1. Force we're trying to move is called the 'load'
    1. Force applied on the lever is called 'effort'
  2. Acts as a force multiplier.
Centre of Mass
1. Point at which the mass is most concentrated.
2. Any freely suspended object will come to rest with the centre of mass directly below the point of suspension.
  1. The object is then in 'equilibrium.'
3. Finding the centre of mass of a irregular shape:
  1. - Suspend the object from one point.
    1. - Drop a plumb line from the same point.
      1. - When it comes to rest mark the point on the shape where the plumb line meets.
        - Re-hang the object from a different point and repeat.
        The point at which the lines cross is the centre of mass.
  2. For a symmetrical shape the centre of mass lies on the line of symmetry/where the lines of symmetry meet.
Moments in Balance
1. For an object in equilibrium:
  1. the sum of the anticlockwise moments = the sum of the clockwise moments
Stability
1. The line of action of the weight acts through the centre of mass.
  1. If the line of action lies outside the base of an object it will topple (as there is a resultant moment).
2. If the base of an object is made wider and the centre of mass is lower, the object will be more stable.
Hydraulics
1. Pressure = Force / area
  1. Pressure = Pa or N/m^2
2. Liquids are virtually incompressible and the pressure in a liquid is transmitted equally in all directions.
  1. So if force is exerted at one point, it will be transmitted to other points in the liquid.
    1. This is used in hydraulic pressure systems.
3. Force exerted by a hydraulic system depends on:
  1. - Force exerted on the system - area of the cylinder on which this force acts on - the area of the cylinder that exerts the force
4. Can be used as a force multiplier.
Circular Motion
1. Centripetal Force: Always acts towards the centre of the circle
2. Centripetal Acceleration: When an object moves in a circle, it's constantly changing its velocity, so we say its accelerating.
3. Centripetal force increases as:
  1. - Mass of object increases
    1. - Radius of circle decreases
      1. - Speed of object increases
Pendulums
1. A pendulum moves to and fro along the same line - known as oscillations.
2. A simple pendulum consists of: a mass (bob) suspended on a string.
  1. When the bob is displaced to the side and let go it swings back and forth through the equilibrium position.
3. Amplitude - distance from equilibrium position to highest position on either side.
4. Time Period - time taken to complete one full oscillation cycle.
  1. eg: highest point to opposite highest point and back again
  2. Increases as length of pendulum increases.
5. Time Period = 1 / frequency

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AQA Physics 3 - Using Physics to Make Things Work

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