Everything Science Grade 12

CHAPTER 6. MOTIONIN TWO DIMENSIONS 6.2

object moving upwards� g g �object moving downwards

Figure 6.1: Objects moving upwards or downwards, always accelerate downwards.

initial height h 0

maximum height

�

(a) time = 0 s

�

(b) time =tm

�

(c) time = 2 tm

Figure 6.2: (a) An object is thrown upwards from height h 0. (b) After time tm, the
object reaches its maximum height, and starts tofall. (c) After a time 2 tmthe object
returns to height h 0.

Equations of Motion ESCCZ

The equations of motionthat were used in Chapter ?? to describe free fall canbe used
for projectile motion. These equations are thesame as those equations that were de-
rived in Chapter ??, but with acceleration from gravity: a = g. We use g = 9,8 m· s−^2
for our calculations.

Remember that when you use these equations, you are dealing with vectors which have
magnitude and direction. Therefore, you need to decide which direction will be the
positive direction so that your vectors have the correct signs.

vi = initial velocity (m·s−^1 ) at t = 0 s

vf = final velocity (m·s−^1 ) at time t

Δx = vertical displacement(m)

t = time (s)

Δt = time interval (s)

g = acceleration due to gravity (m·s−^2 )