Activities 5.1 and 5.2 — What a Force Is and What It Does — Exploring Forces

1. 13 marksCuriosity Grade 8, Chapter 5, page 63, Activity 5.1

   In Activity 5.1 you try to move a large cardboard box in as many different ways as you can. List the ways, and say what every one of them has in common.

   Hint. Fig. 5.1 shows three. Whatever else you invent, check what your hands are doing.

   The ways shown in Fig. 5.1:

   • (a) Pushing the box along
   • (b) Pulling it along
   • (c) Lifting it (which is pulling it up) and carrying it

   Other ways you might have found: sliding it sideways, tipping it over, rolling it end over end, kicking it, dragging it with a rope, or getting a friend to help push.

   What they all have in common. In all the ways that you might have used to move the box, you had to apply a push or pull to the box.

   ✦ Why the activity says 'as many different ways as you can'. The point is not to collect a long list — it is that however inventive you are, you cannot find a way that is neither a push nor a pull. Trying and failing to find an exception is what makes the definition convincing.

   Generally, the push or pull applied on an object is called force in science. Note the word generally: the chapter refines this definition in section 5.3, where it turns out that a force also requires two objects interacting.

2. 24 marksCuriosity Grade 8, Chapter 5, page 64, Activity 5.2

   Copy Table 5.1 and complete it. The book gives three rows — add at least four more of your own, saying in each case whether the force is a push or a pull and what its effect is.

   Hint. Pick examples whose effects are different from one another, not four more of the same.

   The three rows the book gives:

   S.No.	Action	Push/Pull	Effect
   1	Your friend holding your moving bicycle from behind to stop it	Pull	Stopping or decreasing the speed of the bicycle
   2	Hitting a moving ball with a bat	Push	Changing the direction of a moving ball
   3	Pressing an inflated balloon	Push	Change in shape of the balloon

   Rows you can add, chosen so that between them they cover every effect:

   S.No.	Action	Push/Pull	Effect
   4	Kicking a football lying still on the ground	Push	Makes it move from rest
   5	Opening a drawer	Pull	Makes it move from rest
   6	Stretching a rubber band	Pull	Change in shape
   7	Pedalling harder on a bicycle already moving	Push	Increases the speed
   8	Applying brakes on a moving bicycle	Push (on the brake lever)	Decreases the speed
   9	Turning the steering handle of an autorickshaw	Push/pull	Changes the direction of motion
   10	Rolling a chapati	Push	Change in shape
   11	A fielder stopping a moving ball and throwing it back	Push	Stops it, then makes it move again in a new direction

   ✦ Choose your rows to make a point, not to fill space. Row 11 is worth including because it shows one action producing more than one effect, which is the last item in the chapter's list. Rows 4 and 5 are worth having as a pair because one is a push and the other a pull, yet the effect is the same — so push versus pull does not decide what a force does.

3. 33 marksCuriosity Grade 8, Chapter 5, page 65

   What effects can the application of a force have on an object? Give the chapter's full list with an example of each.

   Hint. Five items, and the fifth is not like the others.

   The chapter's list. The force applied on an object may:

   Effect	Example
   make an object move from rest	Kicking a stationary football; opening a drawer
   change the speed of an object if it is moving	Pedalling harder speeds a bicycle up; braking slows it down
   change the direction of motion of an object	Hitting a moving ball with a bat; turning a steering handle
   bring about a change in the shape of an object	Pressing a balloon; stretching a rubber band; rolling a chapati
   cause some or all of these effects	A fielder stops a moving ball and throws it back — stopping it and then starting it off in a new direction

   ✦ The fifth item is not a fifth effect. It is there to stop you thinking of the first four as a menu from which exactly one is chosen. One force can do several things at once — a bat can change a ball's direction and its speed and squash it slightly at the moment of contact.

   A way to hold the list in mind. Three of the effects are about motion (starting it, changing its speed, changing its direction) and one is about shape. The first three are really the same idea seen three ways, since starting from rest is just changing the speed from zero.

4. 43 marksCuriosity Grade 8, Chapter 5, page 65

   The chapter's characters ask: 'Does this mean that whenever there is a change in speed or direction, or change in shape, a force is acting on the object?' and the answer given is 'Yes, none of these take place without the action of force.' Why is this a stronger statement than the list of effects?

   Hint. Read the two statements in opposite directions.

   Because it runs the argument the other way round.

   Statement	What it lets you do
   A force can change speed, direction or shape	Given a force, predict what might happen
   These changes never happen without a force	Given a change, conclude that a force must be acting — even if you cannot see what is causing it

   The second is the more useful of the two, because it turns an observed change into evidence for a force.

   ✦ The chapter uses this immediately, and it is the whole method of section 5.4.1. A ball rolling on flat ground slows down and stops, and no force appears to be acting on the objects. But the speed has changed, so by this rule a force must be acting, even though nothing is visibly touching the ball. That is how friction is discovered a page later — not by seeing it, but by reasoning that it has to be there.

   The same reasoning appears again in exercise question 8: an object in non-uniform motion has a changing speed, so a force must be acting on it. You are not asked to find the force; you are asked to conclude that there is one.

5. 53 marksCuriosity Grade 8, Chapter 5, page 65

   The chapter lists everyday situations where a force is applied (Fig. 5.2): opening a drawer, stretching a rubber band, a fielder stopping a ball, kicking a football, applying brakes on a moving bicycle, rolling a chapati, turning the steering handle of an autorickshaw. Sort them by the effect the force produces.

   Hint. Some of them belong in more than one row — say so rather than forcing a choice.

   Sorted by effect:

   Effect	Situations from the list
   Moves an object from rest	Opening a drawer; kicking a football that is lying still
   Changes the speed of a moving object	A fielder stopping a ball; applying brakes on a moving bicycle
   Changes the direction of motion	Turning the steering handle of an autorickshaw; a fielder returning the ball
   Changes the shape	Stretching a rubber band; rolling a chapati

   ✦ Three of them refuse to sit in one row, and that is the interesting part.

   • Kicking a football that is already rolling changes its speed and usually its direction too, so which row it belongs to depends on the situation, not on the kick.
   • A fielder stopping a ball appears twice above — the ball is stopped, and if the fielder throws it back, it also starts moving in a new direction.
   • Rolling a chapati changes its shape, and the rolling pin also has to be made to move from rest in the first place.

   This is exactly why the chapter's list ends with cause some or all of these effects. A tidy sort is a good exercise, but do not force an example into one box when it honestly belongs in two.

6. 63 marksCuriosity Grade 8, Chapter 5, pages 63-65

   A student says: 'A pull is not really a force — only a push is, because force means pushing something.' Correct this using the chapter.

   Hint. Check the definition, then find a pull that obviously does something.

   The student is wrong, and the chapter's very first definition says so: the push or pull applied on an object is called force in science. Both are forces. The Snapshot repeats it: A force is push or pull on an object.

   Examples of pulls doing every job a push can do:

   Pull	Effect
   Opening a drawer	Moves an object from rest
   A friend holding your moving bicycle from behind to stop it	Decreases the speed — this is row 1 of Table 5.1
   Stretching a rubber band	Changes the shape
   The Earth pulling a fruit off a tree	Moves it from rest, and speeds it up as it falls

   ✦ The most important pull in the chapter is not a push at all. Gravitational force is always an attractive force — the Earth only ever pulls. If pulls were not forces, there would be no gravity, nothing would fall, and Sonali's bicycle would not have run downhill.

   Where the confusion probably comes from. In Fig. 5.1 the box is pushed in (a) and pulled in (b), and (c) — lifting — is labelled by the book as pulling up. Lifting feels like effort rather than like a pull, but the direction of the force on the box is upward, towards you, and that is why it counts as a pull.

   A test that settles any case. Ask which way the force points relative to the object applying it. Towards you is a pull; away from you is a push. Both are forces, since either one can start motion, change it, or change an object's shape.

Solutions written by the tuition.in editorial team and checked against NCERT Curiosity, Textbook of Science for Grade 8, Chapter 5 'Exploring Forces', book pages 62-79 (hecu105.pdf, 18 pages, Reprint 2026-27), downloaded from ncert.nic.in and read page by page. Every activity number, figure number, quantity and quoted sentence below was checked against that PDF. Fig. 5.17 (exercise 10) was MEASURED, not eyeballed: the page was rendered at 1200 dpi and the three cylinders and their waterlines located by colour segmentation. Taking the waterline at the ellipse's mid-height gives submerged fractions of about 82%, 59% and 32% for objects 1, 2 and 3; taking it at the ellipse's top edge gives 69%, 46% and 19%. Both methods give the same strict ordering 1 > 2 > 3, so object 1 displaces the most water, has the largest buoyant force and therefore the largest weight - answer (ii), w1 > w2 > w3. Fig. 5.13's scale was also read directly: NEWTONS 0 to 10 N alongside GRAMS 0 to 1000 g, so 1000 g lines up with 10 N, consistent with the planet table on page 75. Three deliberate restraints on what is claimed. (1) The chapter is entirely qualitative and contains no formula. Nothing here uses F = ma, W = mg, F = Gm1m2/r^2, a value of g, or Newton's laws of motion - none of which is in this book. Balanced forces are named once and explicitly deferred by the chapter to higher grades, and this file defers them too. (2) The swing question in Probe and ponder is answered by distinguishing weight from the seat's upward push, with an explicit note that the chapter does not explain it and that the full account needs later ideas. (3) Buoyancy is explained purely by comparing two forces, as the chapter does, because density is not defined until a later chapter of the same book; the chapter's own phrase 'less dense than water' is quoted only where the book itself uses it.. Questions are referenced from the NCERT textbook for identification.