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Physics Form 4 Chapter 2 Force and Motion I

mv – mu
Implusive force, F =
t
Increasing the time of impact, t to reduce the Decreasing the time of impact, t to increase the
impulsive force, F impulsive force, F

Pestle
Mortar

Figure 2.85 Figure 2.88
1. When a high jumper falls on a mattress, the 1. Pestle and mortar are made of stone. The pestle
Chapter
2 thick and soft mattress lengthens the time of is used to pound spices like chilli, onion and
garlic. The impact time between the pestle and
impact. The impulsive force acting on the high
jumper is reduced and he is less likely to suffer the mortar is very short because of their hard
any injury. and rigid surfaces. The large impulsive force
causes the spices to be crushed easily.

Figure 2.86
2. A long jumper lands on a pit filled with loose
sand. The loose sand lengthens the time of
impact and reduces the impulsive force acting Figure 2.89
on him. 2. A blacksmith uses a heavy hammer and anvil to
3. Figure 2.87 shows a forge metals. An anvil, which is made of steel,
baseball player stopping has a very hard surface. When the hammer
a fast moving ball with knocks on a piece of metal placed on the anvil,
his hand. the short impact time causes a large impulsive
(a) The glove which force to act on the metal.
is made of soft
material lengthens Figure 2.87
the time of impact
and reduces the impulsive force acting on
his palm.
(b) When catching the ball, the player moves
his hand backwards. This action will Figure 2.90
lengthen the time of impact between the 3. A golf club has a very hard hitting surfaces
ball and the glove and further reduce the to give a big force on the golf ball. The hard
impulsive force acting on his palm. surface gives a short impact time and a large
(c) The combined effect of the glove and the impulsive force which can make the ball go far.
action of the hand prevents injury to the
player.

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02 FOC PHYSICS F4 3P.indd 56 29/01/2020 1:39 PM