Why Does A Lemon Float Or Sink In Water? Report Examples

Abstract

Lemons is among the few fruits and vegetable that was found to float in water. An average lemon is heavier than a rice grains. In spite of this, lemons float, while rice grains sink in water. In this study we have demonstrated through experiments that, the ability of an object to float or sink is dependent on its own density and also on the density of the floating medium. It is the density and not weight that determines whether an object floats or sinks in water. By changing the temperature of the medium, we changed the density of water. As the temperature increases, water becomes less dense and more lemons sink into water. When the density of the lemon exceeds that of the floating medium, it sinks. When the lemon has a density equal to or lesser than that of the floating medium, it floats.

Introduction:

Curiosity is the forerunner of all great invention. For examples Newton’s curiosity as why apple fall down, and not fly up, was the forerunner to the discovery of the gravity principal. Likewise the reason for ability of certain objects to float in water was given by Archimedes and his ingenious bath tub experiment, 2,200 years ago. He discovered “buoyancy”, which is upward thrusting force of water on objects. When an objects that is denser is suspended in a fluid of lower density, the buoyant force is not sufficient to keep the object floating, and thus the object sinks. Buoyancy is equal to the weight of the liquid displaced by the object, when dropped into it. The idea that some objects float, and other sink, in spite of having almost the same weight, has motivated scientist to further implore and discover reasons that help similar objects to overcome buoyancy. In an experiment done by Letterman, he observed that while lemon floats in water, lime sinks. In this experiment they choose lemon and lime that weighed exactly the same weight and were of same size. In spite of this, lemon floated, while the lime sunk. This group went on determine the density of the lemon and lime based on the fluid displaced when dropped in water. Weight of the object divided by the water displaced by it will give its density. The scientist noticed that lemon displaced more water (99ml) than lime (90ml). When they divided the weight of each fruit by the volume of water displaced by it, they found that the density of lemon as 1.02 and lime as 1.12g/ml. Though both are closer to density of water that is 1 g/ml, lemon whose density was closest to that of water floated, while the slightly denser lime, sank in water (Stevespanglerscience.com, 2011). In yet another experiment, researchers found that while a whole lemon floats in water, lemon slices sink. They reasoned that, the outer coat of the lemon, was water proof and prevented water from entering into the fluid. When the lemon was sliced to pieces, the exposed pulp was unprotected and water entered into the fruit, causing it become denser, and thus the slices sank, while the whole lemon did not (Planet-science.com, 2015). Some researchers, have tried removing the rind of lemon, before dropping it in water, to test if removing the rind can still make it float (Weirdsciencekids.com, 2015). They argued that, the rind of the lemon have more pores that trapped air, enabling the lemon to float in water. However, lemon continued to float in water, even after the removal of rind, while lime sunk. Though majority of the experiments results reported online, supported the general notion that lemons floats: there are few studies that reported lemon to sink in fresh water, but to float in salt water (Thenakedscientists.com, 2015). Again, the point the researchers made by this study, was that, the lesser the density of the object, than the medium, in which it is suspended, it is more likely to float. The density of salt water is 1.029 gm/ml which is slightly higher than fresh water with a density of 1.0 gm/ml. This is the reason why lemon sink in water and float in salt water. Bar workers who slice lemon and lime so as to present with drink, observed that, lemon slices float on soda water, while lime slices sinks. We also noticed inconsistencies in the results of “Does lemon float or sink experiments” conducted from different lab. While Stevespanglerscience.com reported that rind peeled lemons also floats in water, One Perfect Day, 2013 reported that peeled lemons sink. Yet another researcher, Vijasayee, observed that, on dropping lemon into water, it initially sinks, but after some time rises up and floats on water (R & profile, 2015). When he weighed the lemon before dropping into water and after floating, he noted that the initially weight 35gm of the lemon, increased to 45 gms on floating. He explained this observation, by considering lemon as hypertonic to water. Hypertonic lemon, owing to its high density sinks in water, but with time, water begins to enter the lemon, converting it from hypertonic to hypotonic. This causes lowering of the density of lemon, and it floats in water. As thought by Archimedes, in early days, buoyancy is not simply, the weight of the liquid displaced by the water. Buoyant force depends on the density of the liquid, density of the object suspended in it, and the volume of the liquid displaced. If the force of gravity (Fg) of the lemon overcomes the Buoyant force of the water, then the lemon sinks. Fg = (weight of the lemon) x (gravity). It acts in the downward direction. On the other hand buoyant force acts in the upwards direction. Buoyant force (Fb) = density of the lemon x volume of water displaced x gravity. Fb and Fg act in opposite direction and the net force decides if lemon sinks or floats in water. The ability of the lemon to float depends on the density of the suspending medium. We hypothesise that lemon floats in denser medium and sinks in lighter medium.

Materials and Methods:

Whole lemons, water, chiller, heater, measuring cylinder, fish tanks 30cm x 20 cm, thermometer and hydrometer were used to do this experiment. Four lemon of different sizes were used for the experiment. The density (p) of each lemon was calculated by dividing its weight (w) by its volume (v); (p = w/v). The weight of the lemon was first measured using an electronic balance. To measure the volume of a lemon, a measuring cylinder was filled with water and the lemon was completely immersed into it. The rise in the level of water was noted. The amount of water displaced by the lemon, is its volume. This was obtained by subtracting the final volume (after lemon was immersed) from the initial volume (before the lemon was immersed).
The first fish tank was filled ¾ with normal water (25 oC). The temperature and density of water were recorded. Four lemons of varying sizes were then dropped into the water and after 5 minutes, observation was made. Similar protocol was repeated, using the same four lemon, with cold water (6 0C) and then with hot water (56 0C).

Results:

The density of each of the four lemon are given in Table 1. The temperature of water, density of water and the net number of lemon that floated in each tank are given in Table 2. When the lemons were initially dropped in water kept at normal temperature, two out of the four lemons floated in water. Later when the lemons were drained from normal water, wiped dry and dropped into cold water, three lemon floated and one lemon sank in water. However when the same lemon were placed in hot water, all four of them sank.

Discussion: The notion that heavy object sink in water and light object float is a wrong way to look at the physics of flotations. Heaviness is determined by the weight of the objects. When a small stone of 1gm and a larger stone of 100gms are both thrown in a pond, both the stone sink in water. However when one throws a stone of 10gms along and a wood of 100gms, the small stone sinks, while the heavy wood floats. This is because wood is less dense than a stone. Density and weight are two different thinks. Density is measured by dividing mass by volume (mass/volume). The density of a rock is approximately 2.71 gm/ ml and that of wood is 0.5 gm/ ml. Water has a density of approximately 1 gm/ ml. Hence wood which is less dense than water floats, while rock, having a density higher than water sinks. Dense materials don’t all ways sink in water. For example, steel has a density of 7 gm/ ml, which is greater than the density of water, in spite of this, a ship made of steel floats. This is because, the weight of steel used to build the ship, divided by the volume of the ship is almost equal to the density of water. That is why ship float, even when it is made of steel.
According to Archimedes principal, the upward thrust or the buoyant force of water, prevents an object from sinking (Faculty.wwu.edu, 2015). This buoyant force is equal to the volume of water displaced by object suspended in it. Though the buoyant force is all ways equal to the volume of the liquid displaced, it need not be equal to the force applied by the object on water. When the force applied by the object exceeds the buoyant force, the object sink, though it may displaces water equal to that of a floating object. Thus density determines, whether an object will float or sink in water.
There are a number of factors that alter the density of the floating medium. They include, concentration of atoms in the matter, change in volume and change of phase or state. The volume of the matter can be altered by changing the temperature. As the temperature rises, the medium expands in volume and the density of the medium decreases (Butane.chem.uiuc.edu, 2015). When the temperature is lowered, the medium contracts and becomes denser. This is because density of the floating medium, is mass per unit volume. When one keeps mass a constant and increases volume, the density decreases. From table 1, we understand that the density of water decreases with increasing temperature. The lowering of density, causes lowering in buoyant force, and thus more number of lemon sink with increasing temperature. As the temperature is increased the density of water decreases below that of all four lemons (Table1). Thus all the lemons sink when dropped into water kept at 80oC. Though all liquid become denser when cooled, water has an exception to this rule. Water attains maximum density at 40C. On decreasing the temperature below this, water begins to become less dense. That is why ice cubes float in water (Butane.chem.uiuc.edu, 2015). This phenomenon is attributed to the unique way in which hydrogen bond align within ice crystals.
Conclusion: The density of the object and the density of the floating medium, decides whether an object will float or sink in water. We have verified this hypothesis, by altering the density of water, using temperature and observing the floating behaviour of lemons of known density. Lemons denser than water sink in water, while those lighter than water floated.

References

Butane.chem.uiuc.edu,. (2015). Temperature Effects on Density. Retrieved 8 April 2015, from http://butane.chem.uiuc.edu/pshapley/GenChem1/L21/2.html
Planet-science.com,. (2015). Lemons - do they sink or float?. Retrieved 7 April 2015, from http://www.planet-science.com/categories/under-11s/our-world/2011/05/lemons---do-they-sink-or-float.aspx
R, V., & profile, V. (2015). My Experiments and Results: Why does a lemon sink in water , initially when dropped and and float in water after sometime. Vijaysaayi-experimentsandresults.blogspot.in. Retrieved 7 April 2015, from http://vijaysaayi-experimentsandresults.blogspot.in/p/question-why-does-lemon-sink-in-water_17.html
Stevespanglerscience.com,. (2011). Floating Lemons and Sinking Limes | Experiments | Steve Spangler Science. Retrieved 7 April 2015, from http://www.stevespanglerscience.com/lab/experiments/floating-lemons-and-sinking-limes
.Thenakedscientists.com,. (2015). Why Does A Slice Of Lemon Float But Lime Sinks? - Naked Science Forum. Retrieved 7 April 2015, from http://www.thenakedscientists.com/forum/index.php?topic=14732.0
One Perfect Day,. (2013). Playful Science: Sink or Float Experiment with Lemons - One Perfect Day. Retrieved 7 April 2015, from http://www.oneperfectdayblog.net/2013/07/24/playful-science-sink-or-float-experiment-with-lemons/
Weirdsciencekids.com,. (2015). Floating Lemons Sinking Limes Experiment. Retrieved 7 April 2015, from http://weirdsciencekids.com/floatinglemonssinkinglimes.html