Have you ever wondered why fallen leaves rise in the air or trees sway or bend?
Answer
Because moving air pushes on them — the wind exerts a force on every surface it meets.
A leaf lying on the ground has a large surface for its very small weight. When wind blows across it, the air pushes on that surface, and even a modest push is enough to lift the leaf and carry it along. A tree is far heavier, but its leaves and branches present a very large area to the wind, so the total force on the crown becomes large enough to bend the trunk.
Try this: hold a sheet of paper and a crumpled ball of the same paper in front of a fan. The flat sheet is pushed away hard, the ball hardly at all — the weight is the same, only the area facing the wind has changed.
Q2.
Does the wind exert force on fallen leaves to make them rise or on trees to bend?
Answer
Yes. Moving air exerts a force on whatever it strikes, and that force is what raises the leaves and bends the trees.
We recognise a force by what it does — it can make a resting object move, change its speed or direction, or change its shape. The wind does all of these: a still leaf starts moving, a swaying branch changes direction, a straight trunk bends. Slamming doors, rattling windows and fluttering clothes are the same force showing itself in other ways.
Why it happens: this force spread over the area it acts on is what the chapter calls wind pressure. Thinking in terms of pressure rather than force alone explains why a wide door slams while a narrow window only rattles: the same wind pressure acting on a larger area gives a larger force.
Q3.
Can the shape or size of the straps really make a difference?
Answer
Yes — not to the weight of the bag, but to the pressure that weight produces on the shoulders.
Megha's and Pawan's bags are equally heavy, so gravity pulls both down with the same force. But that force is passed to the shoulders through the straps. Pawan's narrow straps deliver the whole force over a small area of skin, while Megha's broad straps spread the same force over a much larger area. Since pressure is force divided by area, the pressure under the narrow straps is much greater, and it is high pressure on the skin that hurts.
Pressure = Force / Area Same force, smaller area → larger pressure (Pawan's bag) Same force, larger area → smaller pressure (Megha's bag)