AP State Board new syllabus 8th Class Physics Guide 1st Lesson Force and Pressure Textbook Exercise Questions and Answers.
AP 8th Class Physical Science 1st Lesson Questions and Answers Force and Pressure
8th Class Physics 1st Lesson Force and Pressure Questions and Answers (Exercise)
Question 1.
Give two examples each of situations in which you push or pull to change the state of motion of objects.
Answer:
The following are the required examples:
Push force examples :
- A toy car at rest is pushed to move it from one place to another. This changes the state of motion of the toy car.
- A cricket ball hit by a batsman.
- We move a bicycle by pushing it.
Pull force examples:
- Drawing bucket of water from a well by pulling rope.
- Opening a drawer.
- In a game of tug of war, two teams pull the rope in the opposite directions.
Question 2.
Give two examples of situations in which applied force causes a change in the shape of an object.
Answer:
Two examples of force that cause a change in the shape of an object are as follows :
- When plastic bottles are squeezed, they change their shape.
- Pressing the dough in preparing rota.
- ‘A rubber band’s shape changes when it is stretched.
Question 3.
Fill in the blanks in the following statements.
a) To draw water from a well we have to ………… at the rope.
b) A charged body ………… an uncharged body towards it.
c) To move a loaded trolley, we have to ………… it.
d) The north pole of a magnet ………… the north pole of another magnet.
Answer:
a) pull
b) attracts
c) either push or pull
d) repels
Question 4.
An archer stretches her bow while taking aim at the target. She then releases the arrow, which begins to move towards the target. Based on this information fill up the gaps in the following statements using the following terms.
muscular, contact, non-contact, gravity, friction, shape, attraction
a) To stretch the bow, the archer applies a force that causes a change in its …………
b) The force applied by the archer to stretch the bow is an example of ………… force.
c) The type of force responsible for a change in the state of motion of the arrow is an example-of a ………… force.
d) While the arrow moves towards its target, the forces acting on it are due to ………… and that due to ………… of air.
Answer:
a) shape
b) muscular
c) contact
d) gravity, friction
Question 5.
In the following situations identify the agent exerting the force and the object on which it acts. State the effect of the force in each case.
a) Squeezing a piece of lemon between the fingers to extract its juice.
b) Taking out paste from a toothpaste tube.
c) A load suspended from á spring while its other end is on a hook fixed to a wall.
d) An athlete making a high jump to clear the bar at a certain height.
Answer:
a) When squeezing a lemon, the hands exert muscular force on the fruit. As a result, the shape of the lemon gets changed.
b) We use our muscular force to take out paste from a toothpaste tube. The muscular force acts on the toothpaste tube. As result, the shape of the tube gets changed.
c) A downward force is applied to the spring by the suspended weight. As a result, the spring gets stretched. Hence, its shape gets changed.
d) An athlete pushes the ground with his feet. His feet exert a muscular force on the ground. This allows him to jump over the bar. As a result, his state of motion get’s changed.
Question 6.
A blacksmith hammers a hot piece of iron while making a tool. How does the force due to hammering affect the piece of iron?
Answer:
A blacksmith hammers a hot piece of iron. He uses his muscular force. This muscular force changes the shape of the iron so that it can be given a desired shape.
Question 7.
An inflated balloon was pressed against a wall after it has been rubbed with a piece of synthetic cloth. It was found that the balloon sticks to the wall. What force might be responsible for the attraction between the balloon and the wall?
Answer:
An inflated balloon becomes charged when it is rubbed against a wall after being rubbed with synthetic fabric. The balloon attaches to the wall because a charged body attracts an uncharged body. The electrostatic force is the force that exists between the charged balloon and the wall.
Question 8.
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.
Answer:
We make use of muscular force to hold a bucket of water above the ground. This muscular force acts against the force of gravity that pulls the bucket towards the ground. The two forces are equal in magnitude but opposite in direction. Therefore, the net force on the bucket is zero. Hence, there is no change in its state of motion.
Question 9.
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.
Answer:
The force of gravity/weight, which pulls the rocket towards the ground and the force of friction due to earth’s atmosphere, which opposes its motion.
Question 10.
When we press the bulb of a dropper with its nozzle kept in water, air in the dropper is seen to escape in the form of bubbles. Once we release the pressure on the bulb, water gets filled in the dropper. The rise of water in the dropper is due to
a) pressure of water.
b) gravity of the earth.
c) shape of rubber bulb.
d) atmospheric pressure.
Answer:
d) Atomospheric pressure. When air escapes from the dropper’s nozzle, it creates a pressure difference, which causes water to be pulled into the nozzle.
Extended Learning – Activities and Projects
Question 1.
Make a 50cm × 50 cm bed of dry sand about 10 cm in thickness. Make sure that its top surface is levelled. Take a wooden or a plastic stool. Cut two strips of graph paper each with a width of 1 cm . Paste them vertically on any leg of the stool -one at the bottom and the other from the top.
Now gently put the stool on the sand bed with its legs resting on the sand. Increase the size of sand bed if required. Now put a load, say a school bag full of books, on the seat of the stool. Mark the level of sand on the graph strip. This would give you the depth, if any, to which the legs of stool sink in sand.
Next, turn the stool upside down so that now it rests on fits seat on the sand bed. Note the depth to which the stool sinks now. Next, put the same load on the stool and note the depth to which it sinksin the sand. Compare the pressure exerted by the stool in the two situations.
Answer:
Pressure exerted by the stool is greatest in first situation.
Question 2.
Take a tumbler and fill it with water. Cover the mouth of the tumbler with a thick card similar to that of a postcard. Hold the tumbler with one hand while keeping the card pressed to its mouth with your other hand. Turn the tumbler upside down while keeping the card pressed to its mouth.
Make sure that the tumbler is held vertical. Gently remove the hand pressing the card. What do you observe? Does the card get detached allowing the water to spill? With a little practice you will find that the card continues to hold water in the tumbler even after it is not supported by your hand. Also try this activity by using a plece of cloth to hold the tumbler Inan upside down position as shown in the figure.
Answer:
Activity for home
Question 3.
Take 4-5 plastic bottles of different shapes and sizes. Join them together with small pieces of glass or rubber tube as shown in Figure. Keep this arrangement on a level surface. Now pour water in any one of the bottles. Note whether the bottle in which water is poured gets
filled first or all the bottles get filled up simultaneously. Note the level of water in all the bottles from time to time. Try to explain your observations.
Answer:
Water fills in bottles according to air pressure. The bottle which has less air pressure will fill first. This; is because air pressure opposes water flow. However at the end, water level in all the bottles will be same.
8th Class PS 1st Lesson Questions and Answers (Lab Activities)
Activity – 1
1. Table gives some examples of familiar situations involving motion of objects. You can add more such situations or replace those given here. Try to identify action involved in each case as a push and/or a pull and record your observations. One example has been given to help you.
Answer:
Activity – 2
2. Choose a heavy object like a table or a box, which you can move only by pushing hard. Try to push it all by your self. Can you move it? Now ask your friends to help you in pushing it in the same direction. Now push the same object. but ask your friend to push it from the opposite side.
Answer:
Observation : Pushing it in same direction, it moves easily. Pushing it in opposite direction, it does not moves.
Conclusion : Force applied on an object in the same direction add to one another. If the two forces act in the opposite direction on an object, the net force acting on it is the difference between the two forces.
Activity – 3
3. Take a rubber ball and place if on a level surface such as a table top or a concrete floor. Now, gently push the ball along the level surface. The ball begin to move.
Observe there is any change in its speed. Next, place your palm in front of the moving ball. Remove your palm as soon as the moving ball touches it. Observe the speed of the ball.
Answer:
Observation : Ball speed is decreases while moving on the surface. Place palm in front of moving ball, change in speed of ball or direction of its motion.
Conclusion : Force acting on an moving object may bring a change in speed of an object or the direction of its motion.
Activity – 4
4. Take a ball and place it on a level surface. Make the ball move by giving it a push. Now place a ruler in its path. Repeat the activity and try to obstruct the moving ball by placing the ruler in such a way that it makes different angles to its path. In each case note your observations.
Answer:
Observation : The ball not continue to move in the same direction after it strikes the ruler. The ruler makes different angles to moving ball path, the ball moving in different directions.
Conclusion : The speed and the direction of the moving ball change due to the application of a force.
Activity – 5
5. Some situations have been given in Column 1 of Table in which objects are not free to move. Column 2 of the Table suggests the manner in which a force can be applied on each object while Column 3 shows a diagram of the action. Try to observe the effect of force in as many situations as possible. You can also add similar situations using available material from your environment. Note your observations in Columns 4 and 5 of the Table.
Answer:
Activity – 6
6. Take a pair of bar magnets place the longer side of one of the magnets over three round shaped pencils or wooden rollers. Now bring one end of the other magnet near the end of the magnet placed on the rollers. Make sure that the two magnets do not touch each other. Next bring the other end the magnet near the same end of the magnet placed on the rollers. Note what happens.
Answer:
Observation : When the magnets is brought near magnets kept on the pencils, the letter moves away the magnet, showing repulsion. In the second case, bringing the other end of the magnet near the magnet on the pencils makes the latter moves towards the magnet, showing attraction.
Conclusion : We observe that like poles of magnet repels each other and unlike poles of magnet attract each other. It is an example of non-contact force.
Activity – 7
7. Take a plastic straw and cut into nearly two equal pieces. Suspend one of the pieces from the edge of a table with the help of a piece of thread. Now hold the other piece of straw in your hand and rub its free end with a sheet of paper. Bring the rubbed end of the straw near the suspended straw.
Next, rub the free end of the suspended piece of straw with a sheet of paper. Again, bring the piece of straw that was rubbed earlier with paper near the free end of the suspended straw. What do you observe?
Answer:
Observation : A straw rubbed with paper attracts another straw but repels it if it has also been rubbed with a sheet of paper.
Conclusion : We observe that like electrostatic charges are repels each other and unlike electrostatic charges are attracted by each other.
Activity – 8
8. Take a transparent glass tube. The length of the tube should be about 25 cm and its diameter should be 5-7.5 cm. Also take a piece of thin sheet of a good quality rubber balloon. Stretch the ballon tighty over one end of the pipe. Hold the pipe at the middle, keeping it is a vertical position. Ask one of your friends to pour some water in the pipe. You will notice that the bailoon bulges downwards. Note also the height of the water column in the pipe. Pour some more water. Observe again in the bulge in the rubber ballon and height of the water column in the pipe. Repeat this process a few more times. Can you see any relation between the amount of the budge in the rubber balloon and the height of the water column in the pipe.
Answer:
Observation : You observe that the rubber balloon bulges outwards. Now, pour more water into the glass tube. The rubber balloon bulges more.
Conclusion : Liquids exert pressure on the walls of the container.
Activity – 9
9. Take a plastic bottle. Fix a cylindrical glass tube, a few cm long near its bottom. Cover the mouth of the glass tube with a thin rubber balloon. Now fill the bottle upto half with water. You will notice that the balloon bulges. Pour some more water in the bottle. Observe the changes in the bulge of the rubber balloon.
Answer:
Observation : You observe that the rubber balloon bulges out. Now, pour more water in the bottle. You see that the size of the bulge increases.
Conclusion :
- The liquids exert pressure on the base of the container in which they are put.
- Pressure exerted by water at the bottom of the container depends on the height of its column. More is the height, more is the pressure and vice versa.
Activity – 10
10. Take an empty plastic bottle (1 litre). Make four holes, all around near the bottom of the bottle. Make sure that the holes are at the same height from the bottom. Now fill the bottle with water. What do you observe?
Answer:
Observation : You observe that jets of water coming out of the holes fall at same distance from the bottle.
Conclusion : Liquids exert equal pressure at the same depth.
Activity – 11
11. Take a good quality rubber sucker. It looks like a small rubber cup. Press it hard on a smooth plane surface. Rubber sucker stick on the surface. Now try to pull it off the surface. What do you observe?
Answer:
Observation : Rubber sucker is pressed against the smooth plane surface, the air between the sucker and the smooth surface is forced out, reducing the pressure inside. The outer atmospheric pressure being greater, pushes the rubber sucker formly and it adheres to the surface of the smooth plane.
Conclusion : Rubber sucker adheres to the surface of the smooth plane due to the atmospheric pressure acting on it in the downward direction.