NCERT Solutions for Class 4 EVS Chapter 7 - How Things Work

Page No. 105

Activity 1

Q1: Do you think all objects can spin? Make a list of a few objects that can spin. 
Ans: Not all objects can spin. Some objects spin well, but others don’t. Here are a few objects that can spin:

• Top
• Coin
• Bangle
• Wheel
• Fan
• Ball

Q2: Collect the objects mentioned in the table given below. Spin and observe them. Then, complete the table.
Ans:

Page No. 106 - 107

Activity 2

Q: 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.
Ans:

Page No. 108

Discuss

Q1: Which of the spinners did not spin properly? Discuss the possible reasons.
Ans: The spinner with the toothpick away from the centre did not spin properly. It wobbled and fell because it was not balanced. Spinners need the toothpick in the centre to spin well.

Q2: 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?
Ans: Yes, the position of the hole matters. The spinner with the hole in the centre spun well because it was balanced. The spinner with the hole away from the centre wobbled and didn’t spin properly because it was not balanced.

Page No. 110

Activity 3

Q: 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.

From this activity, it can be observed that some heavy objects like iron nails sink, while lighter ones like leaves, float.
Ans: 

Page No. 111

Discuss

Q: Did all the light objects float and all the heavy objects sink? Name the heavy objects that floated and lighter objects that sank.
Ans: Not all light objects float, and not all heavy objects sink. For example:

• Heavy objects that floated: Empty steel bowl (it traps air).
• Lighter objects that sank: Iron nail (it is dense).

Page No. 112

Activity 4

Q: Let us find out whether shape plays a role in floating and sinking.

Ans: 

Page No. 113

Q1: 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. 

Following are some different types of boats which can be made.
Ans: Try to build your boat all by yourself with your group. Use your own ideas, hands, and teamwork to make it special. If something is too tricky, you can ask an elder to guide you—but try doing most of it on your own! Are you ready to become boat builders? Let’s start creating and make our boats float!

Q2: Compare your boat with others’ boats.
Ans:

Page No. 114 - 115

Q1: Enquire about something
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.
Ans: Ravi could ask:

• Why does the spinner slow down and stop?
• How can I make the spinner spin for a longer time?

Q2: Figure it out 
(a) The following figure is bending towards the side ‘A’. What should be done to balance it?

(b) How would you make a floating object sink and a sinking object float?
Ans: (a) To balance the figure bending towards side 'A', add some weight to the opposite side or remove weight from side 'A'. This will make both sides equal and keep it upright.
(b) To make a floating object sink: Add weight or change its shape to trap less air (like pressing aluminium foil into a ball).
To make a sinking object float: Make it lighter or change its shape to trap air (like shaping foil into a cup).

Q3: Do an activity
Classify the objects below based on whether they float or sink in water.
Ans: