Free body diagrams (projectile motion 3.3)

Free body diagram

a clearly labelled sketch showing all of the forces acting on a body at a particular instant in time

• show which forces are acting, in which direction they are acting, where the forces originate and the relative sizes of the forces —> consider the net force acting on the body and therefore the resulting projectile and flight path

three phases of motion within a flight path

1. start of flight

2. mid flight

3. end of flight

weight force does not change over these stages, whereas air resistance may be dependent on the velocity of the moving projectile

E.G. hard-hit shuttle in badminton. air resistance will be far greater at the start of flight after release as it is travelling with the highest velocity —> rapid deceleration of the shuttle in flight, reducing air resistance until its highest point. at its highest point, wight becomes a more dominant force, overall the flight path is non-parabolic

drawing a FBD

• use simple shapes to represent the projectile

• weight and air resistance should originate from the centre of mass (COM) of the projectile

• weight should project downwards

• air resistance should project opposite to the direction of motion

• always include a direction-of-motion arrow

shuttlecock example