Page 1 : Science 8th Std, , 7. Force and Pressure, , 1. Give two examples each of the situations in which you push or pull to, change the state of motion of objects., (i) Push : We close drawer by pushing., We move a wooden box by pushing., (ii) Pull: We draw water from a well by pulling the rope., A horse pulls a cart., , 2. Give two examples of situations in which applied force causes a chang, in the shape of an object., When we apply force on a rubber band to stretch it and on clay to change, , its shape., , 3. Fill in the blanks in the following statements., (a) To draw water from a well we have to pull at the rope., (b) A charged body attracts an uncharged body towards it., (c) To move a loaded trolley we have to push it., (d) The north pole of a magnet repels the north pole of another magnet., , 4. Fillin the gaps :, (a) To stretch the bow, the archer applies a force that causes a change, in its shape, (b) The force applied by the archer to stretch the bow is an example of, , muscular force., (c) The type of force responsible for a change in the state of motion of, , the arrow is an example of a contact force., (d) While the arrow moves towards its target, the forces acting on it, , are due to gravity and that due to friction of air., , (a) Squeezing a piece of lemon between the fingers to extract its juice :, Agents are fingers, object is lemon, effect of force changes the shape of, lemon, , (b) Taking out paste from a toothpaste tube : Agents are fingers of the, person squeezing the tube, object is toothpaste tube and effect of the force, can be observed as the paste coming out of the tube.(change in shape), , :) A load suspended from a spring while its other end is on a hook, , _, , * . ‘ d, fixed toa wall: Agent is the load suspended, object is the spring pal, effort can be seen in the form of elongation of spring on suspension 0, , (change in shape). : ; ;, (d) An athlete making a high jump to clear the bar at a certain height :, , Agent is muscles of athlete, object is athlete himself and effect of the, force changes the state of motion of the athlete., , A blacksmith hammers a hot piece of iron while making a tool. How does, , the force due to hammering affect the piece of iron?, The force due to hammering causes the change in the shape of the iron, , . Aninflated balloon rubbed with a piece of synthetic cloth sticks to, , the wall. What force might be responsible for the attraction between, , the balloon and the wall?, Electrostatic force., , . Name the forces acting on a plastic bucket containing water held above, , ground level in your hand. Discuss why the forces acting on the bucket, , do not bring a change in its state of motion., , Forces acting on bucket are as follows:, , (i) Muscular force of arms acting upward., , (ii) Force of gravity acting downward., , Both the forces do not bring any change in the state of motion because both, of them are acting in equal and opposite directions and thus they cancel each, , other’s effect., , A rocket has been fired upwards to launch a satellite in its orbit. Name, the two forces acting on the rocket immediately after leaving the, launching pad., , The forces that act when a rocket leaves launching pad are as follows:, , (i) Gravitational force of the earth (downward), , (ii) Frictional force of air (in opposite direction), , 10. When we press the bulb of a dropper with its nozzle kept in water, air ir, , the dropper is seen to escape in the form of bubbles. Once we release th, pressure on the bulb, water gets filled in the dropper. The rise of water i, the dropper is due to, , atmospheric pressure