Determine if an object floats or sinks
Scenario
Ek chhoti si iron ki keel paani me doob jati hai, par lohe ka bana ek bohot bada ship paani me araam se tairta rehta hai.
Kya tairna ya doobna is baat par depend karta hai ki object halka hai ya bhari?
Mental model
Tug of War: Gravity versus Buoyancy. Jo jeeta, wo decide karega object kahan jayega.
Jab koi cheez paani mein jaati hai toh uska apna Weight (gravity) use neeche doobana chahta hai, aur Buoyant force use upar thelna chahti hai. Agar density liquid se kam hai, toh buoyancy jeet jati hai aur object tairta hai.
Explanation
Physics mein ek body ka float (tairna) ya sink (doobna) uske mass par nahi balki uski density (mass per unit volume) par depend karta hai. Density basically ye batati hai ki ek particular space mein us object ke atoms kitne densely packed hain.
Agar kisi object ki density liquid ki density se ZYADA (greater) hai, toh iska matlab hai ki us object ka wajan downward us lagne wale upward buoyant force se bada ho jayega. Gravity ki jeet hogi aur object doob (sink) jayega. For example, iron ki density paani se zyada hai, isliye iron nail doob jati hai.
Lekin agar kisi object ki density liquid ki density se KAM (less) hai, toh uspar lagne wala downward gravitational pull weak hota hai in comparison to maximum upthrust (buoyancy). Is case mein buoyant force gravity ko balance kar leta hai aur object paani ki surface par tairne (float) lagta hai. Wood, ice, ya cork ki density paani se kam hoti hai, isliye wo tairte hain.
Lohe ka ship isliye tairta hai kyu ki use aise design kiya jata hai ki andar bahut saari hawa phasi hoti hai. Isse uski OVERALL (average) density paani se kam ho jati hai.
Worked example
Problem: An object has a density of 0.8 g/cm^3. Will it float or sink in water? (Density of water = 1 g/cm^3)
- Pehle hum object ki density aur paani ki density ko compare karte hain.
- Yahan object ki density paani se kam hai.
Answer: It will float in water because its density is less than the density of water.
Problem: A solid block of aluminum has a density of 2.7 g/cm^3. If placed in a pool of water, what happens to it?
- Aluminum ki density ko check karte hain. Ye paani (1 g/cm^3) se kafi heavy (dense) hai.
- Jab object dense hota hai, uski downward gravity buoyant force se jeet jati hai.
Answer: It will sink, because the density of aluminum is greater than the density of water.
Key points
- Density < Liquid: The object floats on the surface.
- Density > Liquid: The object sinks to the bottom.
Common mistakes
- Assuming light objects always float: Bache puchte hain ki ek bhari ship kyu float karta hai. Unko lagta hai mass matter karta hai. Asal mein MASS matter nahi karta, sirf DENSITY matter karti hai.
Recall questions
- What property of a substance determines whether it will float or sink in a given liquid?
- What is the condition for an object to float?
- What happens if an object is denser than water?
Questions & answers
Why does a block of plastic released under water come up to the surface of water?
Because the density of plastic is less than that of water, the upward buoyant force exerted by water on the plastic block is greater than its weight. Therefore, it comes up to the surface.
Approach: Always link density difference to force difference (weight vs buoyant force).
An object has a density of 0.8 g/cm³. Will it float or sink in water (density 1 g/cm³)?
It will float.
Approach: Since 0.8 < 1.0, the object's density is lower than water, so it floats.
Continue learning
Previous: Define buoyant force