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Physics Form 4 Chapter 2 Force and Motion I

Effects of Impulsive Force in Daily short time when it hits the floor. The resultant
Life impulsive force is big enough to crack the tile.
1. During collision, a car undergoes a big change
of momentum in a very short time. From
change of momentum
the equation F = , the
time
impulsive force acting on the car is very big
and can cause serious damage to the car and Figure 2.82
danger to its passengers.
2. A bowl crashes when dropped on the floor. This The Effect of Time on the
is because the bowl undergoes a big change of Magnitude of the Impulsive Force
momentum in a very short time when it hits 1. Consider the formula for impulsive force Chapter
the floor and the resultant impulsive force is
very big. F = mv – mu = Change of momentum 2
t
Time
If the change of momentum is constant, the
magnitude of the impulsive force is inversely
proportional to the time of impact. That is,
1
F ∝ .
t
1
2. Since F ∝ , the shorter the time of impact,
t
Figure 2.81 the bigger the impulsive force. The longer the
3. The tile on the floor cracks after a hammer is time of impact, the smaller the impulsive force.
accidentally dropped on it. The falling hammer Hence, by controlling the value of t, we can
undergoes a big change of momentum in a very control the value of the impulsive force, F.

SPM Highlights

Packaging is an important aspect in industry. The design and structure of packaging requires specific scientific expertise
in order to protect the manufactured products from damage. Figures 2.83 and 2.84 show two examples of packaging for
a computer and eggs respectively. Suggest suitable characteristics of the materials used in the packaging so that the
computer and eggs can be transported and stored safely.

Box
Computer
Polystyrene
Cardboard Eggs

Figure 2.83 Figure 2.84

Answer:
Things that are easily broken are packed using polystyrene or other soft but strong materials. If by accident, these
products are dropped or knocked, the packaging materials can absorb the impulsive force. Their soft surfaces can
reduce the impulsive force by lengthening the time of impact or change of momentum.

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