GCSE AQA Physics 3 Forces

GCSE AQA Physics 3 Forces

1. Moments

   • Moment = Force x Distance from line of action of force to pivot
   • Larger force = larger moment
   • Same force can exert larger moment if distance from pivot is greater
     • To get max. moment - need to push at right angle
   • Total clockwise moments = Total anticlockwise moments
     • Levers use balanced moments
       • Increase distance from pivot at which force is applied
         • Less force is needed to get same moment
           • Levers are force multipliers
             • Make it easier to do work

2. Centre of Mass

   • Point at which whole mass is concentrated
   • Freely suspended object will swing until its centre of mass is vertically below the point of suspension
   • Finding the COM of a flat shape:
     • Suspend shape & plumb line from same point - stop moving
       • Draw line along plumb line
         • Repeat with shape suspended from different pivot point
           • COM is where 2 lines cross
   • With symmetrical shape - can find it using lines of symmetry

3. Stability

   • If moments aren't equal - will be resultant force
   • Most stable objects have wide base & low centre of mass
   • Object will tip over if the line of action of the weight of the object lies outside of the base of the object - causes a resultant moment

4. Pendulum

   • Time taken to swing from one side to other & back - time period
     • Always the same for each swing of given pendulum
     • Time Period = 1 / Frequency
       • Longer pendulum - greater time period

5. Hydraulics

   • Liquids are virtually incompressible & can flow
     • Force applied to one point in liquid transmitted to other points in liquid
       • Pressure in a liquid is transmitted equally in all directions
         • Pressure = Force / Cross-sectional area
   • Hydraulic systems - force multipliers
     • 2 pistons - 1 with smaller cross-sectional area
       • Pressure at both pistons is same
         • At 1st piston - pressure exerted using small force over small area
           • Pressure transmitted to 2nd piston - has larger SA so there is larger force
     • Used in car braking systems & car jacks

6. Circular Motion

   • Velocity is speed & direction - object travelling in circle is constantly changing direction
     • Velocity is constantly changing (not speed) so is accelerating towards centre of circle
       • Must be resultant force causing acceleration - acts towards centre
         • Centripetal force
           • Faster moving object = bigger CF
           • Larger mass = bigger CF
           • Smaller radius = bigger CF