🔹 Upthrust Puzzles 🔹
1. Why does a piece of wood float on water but sink in mercury?
Think about relative densities of wood, water, and mercury.
Wood floats in water as its density is less than water, but in mercury, upthrust is greater, so it floats more easily.
2. Why does a balloon filled with helium rise in air?
Compare the density of helium and air.
Helium is lighter than air, so upthrust on the balloon is greater than its weight, making it rise.
3. Why do swimmers feel lighter in water?
What force acts upward on their body in water?
Swimmers experience upthrust equal to the weight of displaced water, reducing their apparent weight.
4. Why does a stone weigh less in water than in air?
Loss in weight = ?
The stone experiences upthrust in water equal to the weight of displaced water, so its apparent weight decreases.
5. Why does a ship made of iron float on water though iron is heavier than water?
Think about shape and displaced water.
The ship is hollow and displaces a large volume of water, producing upthrust greater than its weight.
6. Why does a diver find it easier to lift heavy objects under water?
What reduces the effective weight?
Upthrust reduces the apparent weight of the object, making it easier to lift underwater.
7. Why does ice float on water?
Compare densities.
The density of ice is less than water, so the upthrust is greater than its weight, and it floats.
8. Why do camels sink less in desert sand compared to horses?
Think about pressure and contact area.
Camels have broad feet, so they displace more sand and experience greater upthrust, sinking less.
9. Why does an iron nail sink in water while a wooden log floats?
Compare densities and displaced water.
The density of iron is greater than water, so upthrust is not enough to balance its weight. Wood is lighter, so it floats.
10. Why does oil float over water?
Compare densities of oil and water.
Oil has less density than water, so water provides more upthrust, making oil float above.
