Page 192 - Physics

Physics for Secondary Schools

Objects falling under the infl uence of gravity
   2 are moving with constant acceleration.
2v
s  2a
2
The equations of motion for a free falling
 4v 2
s  2a body (see Figure 8.26 (a)) will be:
2
(i) v gt=
But,
(ii) h= 1 gt
2
v  2 2
s 
1
2a (iii) v= 2gh
u = 0 m/s
Therefore, s = 4s
2 1

Hence, if the velocity is doubled, the h
stopping distance increases 4 times.

Motion under gravity
If a ball is thrown straight up into the air, (a) Downward motion
it will move upward. However, due to
Earth's gravity, it will momentarily stop,
and then, fall downwards. When the ball v =0 m/s

is falling, the magnitude of its velocity
increases because the direction of its h
acceleration is downwards. The force of
gravity and the acceleration of this body
are always directed downward towards
the centre of the earth. The acceleration (b) Upward motion
in this case is called acceleration due to
gravity, g. The value of g is 9.8 m/s or Figure 8.26: Motion under gravity
2
approximately 10 m/s . Note that, h is being used instead of s and
2
g instead of a. For a body moving/thrown
The point where the ball momentarily downwards, the following equations are
stops is the maximum altitude reached by applied:
the body. Due to constant acceleration, (i) v =+ gt
u
the ball will take the same time to reach 1
its maximum altitude as it does when (ii) h ut= + 2 gt 2
returns to its starting point.
(iii) v = 2 u + 2 2gh

186
Student’s Book Form One

Physics Form 1 Final.indd 186 16/10/2024 20:58