Life Application 1-Rockets, aircrafts and trains are designed in streamline shapes to decrease air resistance.
2-Birds have streamline shape to decrease air resistance. 3-Birds stretch their wings on landing to decrease air resistance.
5-Modern cars have a streamline shape to decrease air resistance. 4-Parachutist opens the parachute to land safely to decrease air resistance.
(6) Ships are designed in streamline shape to decrease water resistance. (7) fish has a streamline shape to decrease water resistance.
The advantages of friction 1- It helps in moving and stopping cars and bicycles. 2-It enables us to control the car speed and to change the car direction.
3-It enables us to walk as the friction between our shoes and the ground prevents us from slipping down. 4-Lightning of a match.
Cars tires with grooves to prevent water from staying between tires and roads. A set of grooves is linked to that channel. Each groove is made in a curved way in which water can squeeze out. If the car moves so fast, there is no enough time for the car tires to squeeze the water out from under them. So water is trapped between the tires and the road and accordingly, friction is reduced to a great extent making it too hard to control the car.
School book page 21 Q(1) a) X in the opposite direction. b)X increase. c) √. d) X is a direct relation. e) increase. Q(2) a) To decrease the water resistance. b) To control the car speed and decrease the accidents. c) Bec. grooves squeeze the water out from under them. d) Bec. They are small balls with very smooth surface put between the internal moving parts of the machine. Q(3) the unfolded one will reach the ground first as it has a smaller area so smaller air resistance.