Activity 5.5 — Magnetic Force — Exploring Forces

1. 14 marksCuriosity Grade 8, Chapter 5, page 69, Activity 5.5

   Describe Activity 5.5 with the two ring magnets. What happens when you try to push the upper magnet down, and what happens when the poles of both magnets are reversed?

   Hint. The wooden stick is not holding the magnet up — check what is.

   The activity. Take two ring magnets and a wooden stick. Hold the stick upright on a wooden table and slide one ring magnet down onto it. Now slide the second ring magnet on above the first, with like poles facing each other (Fig. 5.7).

   What you see.

   Step	Observation
   Second magnet placed with like poles facing	It stays floating above the first, with a visible gap between them
   Push the second magnet down gently	You feel a force pushing back up against your hand; the gap closes a little and springs open again when you let go
   Reverse the poles of both magnets	Like poles again face each other, so it still floats

   ✦ What the wooden stick is for, and what it is not for. It is not holding the magnet up — it only keeps the rings lined up so they cannot slide off sideways. Wood is not a magnetic material, so it plays no part in the force. What holds the upper magnet up is the repulsion between the like poles, acting across an air gap with nothing in between.

   Why the last step is included. Reversing both magnets brings like poles face to face once more — north against north instead of south against south — so the magnet floats again. This shows the effect depends on the poles being alike, not on which particular pole is which.

   If you turn only one magnet over, unlike poles now face each other, they attract, and the upper magnet drops onto the lower one.

2. 23 marksCuriosity Grade 8, Chapter 5, page 69

   Define magnetic force and explain why it is a non-contact force.

   Hint. The definition names both what exerts the force and what it can act on.

   Definition. The force exerted by a magnet on another magnet or a magnetic material is called magnetic force.

   Note the two things a magnet can act on: another magnet, and a magnetic material such as iron.

   Why it is non-contact. Since a magnet can exert a force from a distance without being in contact it is called a non-contact force. Activity 5.5 demonstrates it directly — the upper ring magnet floats with a clear gap below it, so the force is crossing empty space.

   ✦ It can push as well as pull, which not every force can. When two magnets are brought close to each other, like poles (North–North, South–South) repel each other while unlike poles (North–South) attract each other. Both repulsion and attraction are forces — Attraction and repulsion between objects are also a form of push and pull, that is, a force.

   This is what makes gravity different. The chapter points out a few pages later that Gravitational force is always an attractive force, unlike magnetic force or electrostatic force, which can either be attractive or repulsive. Magnetism can push; gravity never does.

   Definition of non-contact force, from the start of section 5.4.2: There are forces whose effect can be experienced even if the objects are not in contact.

3. 33 marksCuriosity Grade 8, Chapter 5, page 69

   What does this section ask you to recall from Exploring Magnets (Grade 6) and from Chapter 4 of this book?

   Hint. Two earlier pieces of learning are being reused here for a new purpose.

   From Exploring Magnets, Curiosity Grade 6:

   • A magnet attracts objects made of magnetic materials.
   • When two magnets are brought close to each other, like poles (North–North, South–South) repel each other while unlike poles (North–South) attract each other.
   • A magnet could exert force on another magnet or a magnetic material without being in contact with it.

   From Chapter 4 of this book, Electricity: Magnetic and Heating Effects: we also learnt about electromagnets which behave like magnets. A coil carrying a current is a magnet, so it exerts magnetic force in exactly the same way — and it can be switched off, which a bar magnet cannot.

   ✦ What is new here is not the fact but the classification. You already knew that magnets attract and repel at a distance. What this chapter adds is that attraction and repulsion are forces, and that acting at a distance makes them a different kind of force from muscular force and friction. The observation is old; the category is new.

   The chapter's own bridging question makes this explicit: Is it essential for an object applying force on another object to always be in contact with it? Magnetism is the first example that answers no, and electrostatic and gravitational force follow.

4. 43 marksCuriosity Grade 8, Chapter 5, pages 66-72

   Sort these into contact and non-contact forces, giving a reason for each: a bullock pulling a cart, a compass needle turning to point north, a coin sinking in water, a charged balloon lifting a hair, a fruit falling from a tree.

   Hint. For each one, ask whether anything is touching the object at the moment the force acts.

   Situation	Force	Contact or not	Reason
   Bullock pulling a cart	Muscular force	Contact	The animal is joined to the cart through the yoke and ropes — an unbroken chain of touching
   Compass needle turning to point north	Magnetic force	Non-contact	Nothing touches the needle; the Earth's magnetic field acts across a distance
   Coin sinking in water	Gravitational force pulling it down	Non-contact	The Earth pulls the coin without touching it. (The water also exerts a buoyant force on it, and that is a contact force)
   Charged balloon lifting a hair	Electrostatic force	Non-contact	This force comes into play even when the objects are not in contact
   Fruit falling from a tree	Gravitational force	Non-contact	The Earth attracts it from a distance

   ✦ The coin is the one to think about carefully. It is easy to write 'contact, because the coin is touching the water'. But the question is which force you are naming. The force making it sink is the Earth's gravitational pull, and the Earth is not touching it. The water is touching it, and does exert an upward buoyant force — just not the one that sends the coin down.

   Naming the two objects settles every case. Bullock and cart — touching. Earth and fruit — not touching. Once you have written both objects down, the classification is no longer a matter of judgement.

   The chapter's three non-contact forces are magnetic, electrostatic and gravitational; its two contact forces are muscular force and friction.

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.