1Why do objects sink or float?
2Oil, which is less dense than water, floats on the surface of water. Can an object made of iron, which is denser than water, also float on water?
3If a hole is formed at the bottom of a floating boat, it sinks. Why?
4Why does a balloon filled with helium float in the air?
5On which law or principle is a lactometer based: Pascal's law, Archimedes' principle, the law of gravitation or Newton's law?
6What is the condition for a hydrogen balloon to fly upwards in the air?
7When a ship enters a river from the sea, it is found to sink more than before. What is the reason for this?
8Differentiate between the reason for a steel pin sinking in water and a steel plate floating on water.
9Differentiate between the process of a hot air balloon sinking and rising in the air.
10Give a reason: a wooden cork dipped below the surface of water by pressing it with a finger comes to the surface when the finger is removed.
11Give a reason: we feel lighter while floating on water.
12Give a reason: it is easier to float in the Dead Sea than in a swimming pool. (The density of water in the Dead Sea is 1240 kg/m³.)
13Give a reason: if more passengers climb a boat than its maximum capacity, the boat is likely to sink.
14Mention the forces acting on a floating object and their directions.
15State the law of floatation.
16When a stone is dropped into water, it sinks. Does this happen because of the absence of upthrust?
17Substances with a density greater than the density of a liquid sink in it. Is this statement always true? Justify with an example.
18Two balloons, one filled with air and the other with hydrogen, look identical. What difference can be noticed when they are released into the air? Explain with reasons.
19An object is floating just below the surface of water. If the amount of salt dissolved in the water goes on increasing, what change will occur in the position of the object? Explain with reasons.
20A weighing machine carries a beaker of water. In case (a) the beaker is only partly filled and the machine reads 20 N; a floating block of weight 5 N, and in another trial a floating block of weight 8 N, is placed in it. In case (b) the beaker is filled to the brim and the machine reads 30 N; the same 5 N and 8 N blocks are placed in it and water spills over the edge. What does the machine read each time? Explain with reason.
21When a person puts a lactometer into milk, the whole of its narrow stem sinks into the milk. What conclusions can be drawn from this event?
22A wooden block of mass 2 kg floats in water. If the density of water is 1000 kg/m³, what mass and what volume of water does the block displace?
23How does the way a submarine rises and sinks differ from the way a fish does?
24Why does a helium balloon stop rising at a certain height, and why does it finally burst?