# Chapter 2 Force and Motion 2-2

January 3, 2015  |  By  |

Mr Ng Han Guan Form 4 Chapter 2: Force and Motion Guru Cemerlang Physics MSAB Date: 2 nd edition © 2011 | chp 2 | Maktab Sultan Abu Bakar | Sekolah Kluster Kecemerlangan 14 2.6.1 Situations Involving Impulsive Forces SITUATIONS EXPLANATION SITUATIONS EXPLANATION Thick mattresses with a soft surface are used in events such as the high jump so that the time interval of impact on landing is increased , thus reducing the impulsive force . Hammer and nail are made of metal. When a hammer hits at a nail, the collision time is small and hence the impulsive force is great . So the nail penetrates a wooden material easily. In games like baseball, cricket and softball, the catcher always pulls his hand backward when catching the ball to lengthen the collision time and hence reduces the impact of the impulsive force . An exponent of karate has the capability to split a thick wooden slab by bringing his hand down hard onto the surface of the wood. The momentary contact produces a great impulsive force which splits the wooden slab. A high jumper will bend his legs upon landing. This is to increase the time of impact in order to reduce the impulsive force acting on his legs. This will reduce the chance of getting serious injury. Pestle and mortar are made of stone. When a pestle is used to pound chillies the hard surfaces of both the pestle and mortar cause the pestle to be stopped in a very short time . A large impulsive force is resulted and thus causes these spices to be crushed easily. 2.7 Being Aware of the Need for Safety Features in Vehicles 1. Crumple zones  In a crash, the bonnet and boot of the car is designed to crumple, making the collision last a slightly longer time. The chassis contains parts that have grooves or beads cast into them. In a collision, these beads act as weak points in the members, causing them to crumple in a concertina shape. The force exerted on the car (and on its passengers) is then smaller. 2. Strong steel struts or framework of the car  The strong steel strut prevents the collapse of the front and back of the car into the passenger compartment. Also gives good protection from a side-on collision.