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NCERT Solutions Curiosity Chapter 5 Chapter opener — Probe and ponder

Book page 62 Updated on2026-09-05

Q1.
Why does it feel harder to pedal a bicycle when going uphill than on flat ground?
Answer

Because on a slope you are pedalling against the pull of the Earth, and on flat ground you are not.

On level ground the Earth pulls the cycle and you straight down, into the road. That pull does not oppose your forward motion at all — the only forces your muscles have to overcome are the friction of the road and tyres and the friction of the air. On a hill, every turn of the pedal also lifts you and the cycle a little higher, so now your muscular force has to work against gravity as well. The same speed therefore needs a much bigger push on the pedals, and that is what feels hard.

Why it happens: a force is needed to move an object; the steeper the road, the larger the share of the Earth's pull that acts backwards along the slope and opposes you. Add the fact that hill roads are often rough — greater friction — and pedalling becomes harder still.
Check it yourself: notice what the story says next. Coming down the slope the girls stop pedalling and still speed up. The same gravitational force that opposed them going up now acts along their motion, so no muscular force is needed at all.
Q2.
Why is it easier to slip on a wet surface?
Answer

Because water gets into the tiny irregularities of the two surfaces and keeps them slightly apart, so the force of friction between your foot and the floor becomes very small.

Even a floor that looks perfectly smooth has a large number of minute bumps and hollows (Fig. 5.6), and so does the sole of your shoe. When they are pressed together these irregularities lock into one another and oppose sliding — that opposition is friction, and it is what lets your foot grip the floor and push backwards while you walk. A film of water fills the hollows and floats the two surfaces apart. The irregularities can no longer interlock, friction drops sharply, your foot slides instead of gripping, and you slip.

Did you know? This is exactly why bathroom tiles are made with a rough, grooved surface and why tyres have a tread pattern cut into them — the grooves let water escape so that the raised parts can still touch the road and provide friction.
Q3.
Why do we feel ‘light’ or like we are ‘floating’ just after our swing reaches its highest point and begins to come down?
Answer

Because at that moment you and the seat are falling together, so the seat stops pressing up on you as hard as it usually does — and it is that push of the seat, not the Earth's pull, that we actually feel.

Sitting still on a swing, the Earth pulls you down and the seat pushes you up by an equal amount; the two balance and you feel your normal weight through the seat. At the highest point the swing stops for an instant and then starts moving down. While it is moving down, the seat is dropping away beneath you and its upward push on you becomes much smaller. Less push under you is felt as lightness — the same sensation as in a lift that has just started going down.

Why it happens — and what does not change: your mass is the same, and the Earth's pull on you (your weight) is the same as always. Only the contact force from the seat has changed. Feeling light is not the same thing as weighing less.
Q4.
Share your questions
Answer

Frame questions that begin with why, how, what if or where — questions whose answer needs a force to be named and its direction stated. Write them in your notebook and take them to your class.

Sample questions:

  • Why does a cyclist have to pedal harder against the wind, when the wind is not touching the cycle's wheels?
  • If friction always slows things down, how are we able to walk at all?
  • What would happen to the reading of a spring balance if the same object were weighed at the top of a very high mountain?
  • A magnet attracts an iron nail without touching it. Does the nail also pull the magnet?
  • Why does a heavy iron ship float while a small iron nail sinks?
Tip: the best questions in this chapter are the ones you can test. Two of the five above can be checked with a spring balance, a magnet and a bucket of water in your own classroom.
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