AQA Physics 3 - Using Physics to Make Things Work

AQA Physics 3 - Using Physics to Make Things Work

1. Moments

   • The turning effect of a force
     • Size of the moment is given by
       • M= f x d
         • D(istance) from the pivot - m
   • To increase the moment:
     • - Increase the distance to the pivot
       • - Increase the force
   • Levers
     • Force we're trying to move is called the 'load'
       • Force applied on the lever is called 'effort'
     • Acts as a force multiplier.

2. Centre of Mass

   • Point at which the mass is most concentrated.
   • Any freely suspended object will come to rest with the centre of mass directly below the point of suspension.
     • The object is then in 'equilibrium.'
   • Finding the centre of mass of a irregular shape:
     • - Suspend the object from one point.
       • - Drop a plumb line from the same point.
         • - 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.
     • For a symmetrical shape the centre of mass lies on the line of symmetry/where the lines of symmetry meet.

3. Moments in Balance

   • For an object in equilibrium:
     • the sum of the anticlockwise moments = the sum of the clockwise moments

4. Stability

   • The line of action of the weight acts through the centre of mass.
     • If the line of action lies outside the base of an object it will topple (as there is a resultant moment).
   • If the base of an object is made wider and the centre of mass is lower, the object will be more stable.

5. Hydraulics

   • Pressure = Force / area
     • Pressure = Pa or N/m^2
   • Liquids are virtually incompressible and the pressure in a liquid is transmitted equally in all directions.
     • So if force is exerted at one point, it will be transmitted to other points in the liquid.
       • This is used in hydraulic pressure systems.
   • Force exerted by a hydraulic system depends on:
     • - Force exerted on the system - area of the cylinder on which this force acts on - the area of the cylinder that exerts the force
   • Can be used as a force multiplier.

6. Circular Motion

   • Centripetal Force: Always acts towards the centre of the circle
   • Centripetal Acceleration: When an object moves in a circle, it's constantly changing its velocity, so we say its accelerating.
   • Centripetal force increases as:
     • - Mass of object increases
       • - Radius of circle decreases
         • - Speed of object increases

7. Pendulums

   • A pendulum moves to and fro along the same line - known as oscillations.
   • A simple pendulum consists of: a mass (bob) suspended on a string.
     • When the bob is displaced to the side and let go it swings back and forth through the equilibrium position.
   • Amplitude - distance from equilibrium position to highest position on either side.
   • Time Period - time taken to complete one full oscillation cycle.
     • eg: highest point to opposite highest point and back again
     • Increases as length of pendulum increases.
   • Time Period = 1 / frequency