In this lab students are taking a raw egg still in its shell and attempting to make it float by changing the density of the water (adding salt to the water to increase the overall density of the water).
The general rule of thumb for this experiment is roughly 1 tablespoon per ounce of water will make the egg float.
Each kid will add different amounts of water to their cup and will measure with their spoon slightly differently, my rule of thumb is if the kids can show their work and describe whether or not anything changes then they have been successful in their experiment.
Buoyancy Challenge Questions – These questions are meant to test and exceed the knowledge that the kids gained during the Buoyancy Lab. These questions will be challenging for the older students and you should not feel discouraged if you do not get the answers or understand what is going on.
1) The density of a rock is 12 g/mL (grams per milliliter) and the density of a glass of brine (salt with water in it) is 20 g/mL (grams per milliliter). What will happen to the rock when put in the brine?
a. It will sink
b. It will submerge in the water but will not sink
c. It will float at the top of the water
d. I do not know
The rock has a density much lower than the density of the brine and should float at the top of the water. There are instances where it may sink, think about a clump of mud that is dry, putting it in the water it may absorb the water and possibly become the same density as the brine and sink into the water but not to the bottom or may become more dense than the brine and may sink all the way to the bottom. Buoyancy can get very tricky when materials are hydrophilic (water loving, meaning that they absorb water readily). It can also be very interesting when things are hydrophobic (water disliking, meaning that they curl up or change conformation to avoid water interacting with them, think about oil do oil and water mix? No, that is because oil is hydrophobic).
2) Can you change how buoyant an object is in a certain fluid without changing the fluid at all?
a. Yes
b. No
c. Maybe
d. I do not know
Yes, let's use a common example of a boat. A lot of boats are made of wood, metal and fiberglass. The fiberglass can have a very low density and may have a positive buoyant force on its own, but what about the metal? Most metals are fairly dense and if I was to throw a ball of aluminum foil in a cup of water it would invariably sink, but what if I take that same ball of foil and instead of balling it up I make it into a little boat shape, what will happen? Provided there is no a way for the water to enter the inside of your little boat it should float, this is an example of surface tension and surface area countering acting the gravity force to make something of higher density float in a fluid of lower density.
3) Can an object have different buoyancies (positive, neutral and negative) in different liquids?
a. Yes
b. No
c. Maybe
d. I do not know
Yes, think about oil and water. If I add a cotton ball to the water it will float, but will eventually sink because cotton is hydrophilic and the ball will become filled with water adding to the density of the cotton and making it more dense than the water and causing it to sink. Now stick a fresh cotton ball into the oil, the oil does not penetrate the cotton like the water and the cotton ball should remain floating in the oil. So in this instance the cotton ball has a negative buoyancy in the water and a positive buoyancy in the oil (even though the oil is less dense than water, crazy cool, huh?)
4) Can changing the surface area of an object make it buoyant in a fluid even though its density might be much greater than the density of that fluid?
a. Yes
b. No
c. Maybe
d. I do not know
Yes, look back at the explanation for question 2
5) Can the buoyancy of an object be different when in a different area of fluid in the same container?
a. Yes
b. No
c. Maybe
d. I do not know
Yes. Now this is a crazy concept and has to do with pressure gradients in a liquid. Think about the ocean, brine (salt water) in a large container. Now the saltiness of the water can change from place to place and at the bottom of the ocean where the pressure is very high you can have a separation of the brine into supersaturated (having more salt in the water than it normally could under regular circumstances) and normally saturated brine. This creates a phenomena know as brine lakes that exists on the ocean floor and are home to amazing forms of life.
Buoyancy Challenge Questions – These questions are meant to test and exceed the knowledge that the kids gained during the Buoyancy Lab. These questions will be challenging for the older students and you should not feel discouraged if you do not get the answers or understand what is going on.
1) The density of a rock is 12 g/mL (grams per milliliter) and the density of a glass of brine (salt with water in it) is 20 g/mL (grams per milliliter). What will happen to the rock when put in the brine?
a. It will sink
b. It will submerge in the water but will not sink
c. It will float at the top of the water
d. I do not know
The rock has a density much lower than the density of the brine and should float at the top of the water. There are instances where it may sink, think about a clump of mud that is dry, putting it in the water it may absorb the water and possibly become the same density as the brine and sink into the water but not to the bottom or may become more dense than the brine and may sink all the way to the bottom. Buoyancy can get very tricky when materials are hydrophilic (water loving, meaning that they absorb water readily). It can also be very interesting when things are hydrophobic (water disliking, meaning that they curl up or change conformation to avoid water interacting with them, think about oil do oil and water mix? No, that is because oil is hydrophobic).
2) Can you change how buoyant an object is in a certain fluid without changing the fluid at all?
a. Yes
b. No
c. Maybe
d. I do not know
Yes, let's use a common example of a boat. A lot of boats are made of wood, metal and fiberglass. The fiberglass can have a very low density and may have a positive buoyant force on its own, but what about the metal? Most metals are fairly dense and if I was to throw a ball of aluminum foil in a cup of water it would invariably sink, but what if I take that same ball of foil and instead of balling it up I make it into a little boat shape, what will happen? Provided there is no a way for the water to enter the inside of your little boat it should float, this is an example of surface tension and surface area countering acting the gravity force to make something of higher density float in a fluid of lower density.
3) Can an object have different buoyancies (positive, neutral and negative) in different liquids?
a. Yes
b. No
c. Maybe
d. I do not know
Yes, think about oil and water. If I add a cotton ball to the water it will float, but will eventually sink because cotton is hydrophilic and the ball will become filled with water adding to the density of the cotton and making it more dense than the water and causing it to sink. Now stick a fresh cotton ball into the oil, the oil does not penetrate the cotton like the water and the cotton ball should remain floating in the oil. So in this instance the cotton ball has a negative buoyancy in the water and a positive buoyancy in the oil (even though the oil is less dense than water, crazy cool, huh?)
4) Can changing the surface area of an object make it buoyant in a fluid even though its density might be much greater than the density of that fluid?
a. Yes
b. No
c. Maybe
d. I do not know
Yes, look back at the explanation for question 2
5) Can the buoyancy of an object be different when in a different area of fluid in the same container?
a. Yes
b. No
c. Maybe
d. I do not know
Yes. Now this is a crazy concept and has to do with pressure gradients in a liquid. Think about the ocean, brine (salt water) in a large container. Now the saltiness of the water can change from place to place and at the bottom of the ocean where the pressure is very high you can have a separation of the brine into supersaturated (having more salt in the water than it normally could under regular circumstances) and normally saturated brine. This creates a phenomena know as brine lakes that exists on the ocean floor and are home to amazing forms of life.
No comments:
Post a Comment