NCERT Solutions for Class 4 EVS Chapter 07 How Things Work

Question 1. Do you think all objects can spin? Make a list of a few objects that can spin.
Answer: Not every object has the ability to spin. Some things can rotate with ease, while others cannot rotate at all. Here are several objects that are able to spin:
- Coin
- Bottle cap
- Lattu
- Football
- Ceiling fan
In simple words: Some objects can turn around in circles, but others cannot. Coins, tops, and fans are good examples of things that can spin.

Exam Tip: When listing objects, think about their shape - round or circular objects tend to spin better than objects with corners or uneven surfaces.

Question 2. Collect the objects mentioned in the table given below. Spin and observe them. Then, complete the table.
Answer: This is an observation-based activity where you spin different objects and record what happens. Here is a completed table based on typical observations:

Exam Tip: Focus on describing what you actually see - how fast it spins, how long it spins, and what sounds or movements happen as it slows down.

Question 3. Collect things, such as pieces of cardboard, toothpicks, an empty tube of a ballpoint pen, and other small objects. Make the following spinners. Spin them and record your observations.
Answer: This is a hands-on activity where you make different types of spinners and observe how they behave. Here are the observations from the activity:

Exam Tip: Pay close attention to the position of the toothpick and how it affects spinning - this shows the importance of balance in rotation.

Question 4. Which of the spinners did not spin properly? Discuss the possible reasons.
Answer: The spinner that had the toothpick placed away from the middle did not spin well. This occurred because the spinner lacked balance. When the hole is positioned off-centre, the spinner becomes unstable and falls over quickly rather than continuing to rotate smoothly.
In simple words: The spinner with a stick that is not in the middle does not work. This is because it is not balanced. A balanced spinner spins better and lasts longer.

Exam Tip: Always mention the term "balance" or "balanced" when explaining why a spinner works or does not work - this is key to the concept of rotation.

Question 5. Have you noticed the position of the hole in the first two spinners? Did this difference in the position of the hole make a difference in the spinning of these spinners?
Answer: Yes, I did observe the difference in hole position in the first two spinners. The first spinner had its hole in the middle, which kept it balanced and let it rotate for a much longer period. However, the second spinner had its hole away from the middle and did not spin well. Thus, yes, the hole's location made a very important difference.
In simple words: A hole in the middle makes the spinner spin well. A hole on the side makes the spinner not work properly. Position of the hole matters a lot.

Exam Tip: Always compare the two spinners directly - mention that the centered hole is the key reason the first spinner worked better than the second.

Question 6. Collect objects, such as a leaf, an iron nail, an empty bowl (katori), a plastic bottle with a lid, pieces of stone, aluminium foil and other things of your choice. Fill a bucket with water. Before dropping the things listed in the table, guess whether things will float or sink. You may try other things too. Then, observe what happens when it is actually dropped in water. You can write 'F' for objects that float and 'S' for objects that sink.
Answer: This is an observation activity where you predict and then test whether different objects float or sink in water. Here is the completed table based on typical outcomes:

Exam Tip: Remember that whether something floats or sinks depends not just on weight, but also on whether there is air or empty space inside it.

Question 7. Did all the light objects float and all the heavy objects sink? Name the heavy objects that floated and lighter objects that sank.
Answer: No, not all light objects stayed on top and not all heavy objects went to the bottom. An empty steel bowl was heavy but it floated on the water. An iron nail or pin was light yet it sank to the bottom.
In simple words: Weight alone does not decide if something floats or sinks. A heavy bowl can float, and a light nail can sink. The shape and whether there is air inside also matter.

Exam Tip: This question teaches an important lesson - do not judge floating and sinking by weight alone; shape and air pockets are equally important.

Question 8. Let us find out whether shape plays a role in floating and sinking.
Answer: Yes, shape plays a very important role in whether objects float or sink. Here are the observations when aluminium foil is changed into different shapes:

Exam Tip: The key learning is that trapped air helps objects float - shapes with hollow spaces trap air, while solid shapes do not, which is why shape matters more than just the material itself.

Question 9. Let us create some boats: Collect some paper, cardboard boxes, ice-cream sticks, clay, adhesive tape, etc. Create groups of three to four students. Think of how you can make a boat using some of the materials that you have. Draw a picture. Prepare a boat. Try to ensure that your boat is different from boats made by other groups. Organise an exhibition of boats in the class.
Answer: This is a creative hands-on project where you design and construct your own boat using available materials. The goal is to make a working boat that floats in water and is unique compared to boats made by classmates. You can use paper, cardboard, ice-cream sticks, clay, tape, or any other suitable materials. After building your boat, you may display it along with boats from other groups in a classroom exhibition. Several examples of boats that can be made include: a boat built with ice-cream sticks, a boat made from a coconut shell, or boats made using walnut shells.
In simple words: Make your own boat using materials like paper or sticks. Try to make it look different from other boats. Float it in water to see if it works. Show all the boats together in your classroom.

Exam Tip: Design your boat to be stable and wide enough to not tip over easily - test it in water and make changes if needed before the class exhibition.

Question 10. Compare your boat with other boats.
Answer: When comparing boats with others, look at the strengths and challenges of your design. Strengths might include good floating ability, sturdy construction, or an interesting design. Challenges might include tipping over easily, taking in water, or using too many materials. Create a table with two columns - one for your boat's strengths and one for its challenges - to organize your observations.
In simple words: Look at how your boat works compared to other boats. Think about what is good about your boat and what problems it has. Write these down.

Exam Tip: Be honest in comparing - note both what works well in your design and what you might improve, as this shows good observational and critical thinking skills.

Question 11. When Ravi spins a spinner, he notices that it slows down and eventually stops. He is curious about this and asks his teacher some questions. List at least two questions that he could ask.
Answer:
(i) Why does the spinner slow down after some time?
(ii) What makes the spinner stop spinning?
In simple words: A spinner always slows down and stops. We can ask why this happens and what force stops it from spinning.

Exam Tip: When writing questions, use "Why" and "What" to encourage thinking about causes and reasons - these are better questions than simple "yes/no" questions.

Question 12. (a) The following figure is bending towards the side 'A'. What should be done to balance it?
Answer: To balance the figure that is bending towards side A, you have three options: (1) place more weight on side B to balance the weight on side A, (2) take away the object from side A to reduce the weight there, or (3) move the weight towards the centre point so it is more balanced.
In simple words: If one side is heavier, you can add weight to the other side, remove weight from the heavy side, or move things closer to the middle to balance it.

Exam Tip: The key principle is balance - whatever weight you add or remove should make both sides equal in their force or distance from the centre point.

Question 12. (b) How would you make a floating object sink and a sinking object float?
Answer:
To make a floating object sink: Add weight to it, or try changing the shape of the object if you can.

To make a sinking object float: Attach something light, such as a sponge, to it, or try changing the shape of the object if possible.
In simple words: To make something that floats go down, add heaviness to it. To make something that sinks go up, attach something light to it or change its shape.

Exam Tip: Remember the two main ways to change floating and sinking are: (1) adding or removing weight, and (2) changing the shape to trap or release air.

Question 13. Classify the objects below based on whether they float or sink in water.
Answer: Below is the classification of objects into those that float and those that sink:

Exam Tip: Notice patterns - objects made of materials with air pockets or low density tend to float, while solid dense materials tend to sink.