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Answers to Readers' Questions on Physics:
List of next 10 items
- Salt needed to float an egg
- How does a burning candle float?
- How can salt make water denser?
- Trying to find density of piece of wood
- Is clay buoyant and cooking oil?
- Building a boat for science project
- Questions about displacement
- Adding boat to container of water
- Weight of tub of water with person floating in it
- Is cooking oil more dense than water?
April 2, 2007
How much salt do you need in tap water to float an egg that just came out of the refridgerator? Please give the answer to me quick, I have a science fair coming up soon.
Sarah - USA
You need to measure the temperature of the water and the egg, because the amount of salt varies with temperature. If this is a science fair project, you really need to do the experiment to find out the amount for the given conditions.
March 4, 2007
we are doing a science project on how and why things float do you think you could answer our question? why do floating candles float higher in the water as they burn? thanks
As far as I can see, the ratio of the candle above water and below water would remain the same as the candle burned. It might look like it is floating higher, because there is less candle under the water after it has burned some.
For example, if the candle burned to one half the size, the amount under the water would be one half that it was previously.
Since you would probably put a weight on one end of the candle to keep it up right in the water, it would actually be a little lower than before because of the weight.
I've never tried this experiment, so there may be some trick for something I am not aware of, if it really does fold higher in the water.
February 28, 2007
I want to ask 2 questions. =)
1) Why and how can salt makes the water denser?
2) If possible, can you give me an example of 2 different kinds of fruits (should weigh about the same)that one is denser than the other?
Lindsay - Hong Kong
Salt dissolves in water and its atoms become ions and locate between the water molecules. That means there is extra mass or weight in a given amount of water.
Pick up an orange and an apple. They are about the same size, but the orange is heavier than the apple, and thus it is denser. Density = mass divided by volume.
January 31, 2007
Okay I understand that you cannot get the density of wood by water dispurtion because it is not heavy enough to dispurse the water in volume but if it an irregular shape piece of wood how would measure the density????
ann - USA
Fill a container to its top with water. Carefully hold the irregular piece of wood under the water, perhaps using something like a thin piece of metal that has little volume. Measure the volume of the water that runs out of the container. That is the volume of your piece of wood.
January 30, 2007
If you were to put clay in cooking oil would it be buoyant and why? i know why but i wanna a clearer answer
a - Canada
If the clay was less dense than the cooking oil, it would be buoyant. The density is the mass divided by the volume. I don't know the type of clay used, so I don't know its density. But if the clay was hollow, such as a small boat, it might easily float.
October 3, 2006
I have a project for science class. I have to built a boad that will float the best when weight is added to it.
What materials will work the best? I need to have all materials and the boat built by next week.
Danielle - USA
The best type of boat would be something that is hollowed out. Try a plastic shoe box. You can add weight to it until the water comes over the sides. If the box has a sealed top on it, you can add even more weight.
March 28, 2006
HI I AM LISA IN GRADE 8
I HAVE 4 QUISTOINS ABOUT DESPLACEMENT
1)CAN THE VOLUME BE DONE FOR FINDING THE DISPLACEMENT FOR EACH SUBSTANCE?
2)WHAT HAD TO BE DONE FOR FINDING THE DISPLACEMENT OF SUBSTANCE THAT FLOATWED?
3)WHY DO WE ALWASYS MEASURE THE MASS AND THE VOLUME BEFORE FINDING THE DISPLACEMENT OF EACH ITEM?
4)WHY DID SOME SUBSTANCES FLOAT WHILE OTHERS SANK IN WATER?
THANKS ALOT FOR ANSWRING IT.
LISA - CANADA
You can put an object in a full container of water and collect the water that runs over. The volume of that water will be how much was displaced. If the object sinks, the volume of the water will be the same as the volume of the object. If it floats, then it will be just what is under water.
March 20, 2006
Assume that a large container is supported by a wooden frame designed to support the container's weight filled half full with water. Thus the frame must withstand ther weight of the container and water.
Float a 5 lb. toy boat, buoyancy and displacement will have no effect on the weight. But now sink the boat so that it rests on the bottom. Will this increase the weight and cause the support to collapse? Bear in mind that the container and water will continue to remain the same and the boat weighs 5 lbs. The support is onl able to carry the weight of the water and container.
Patrick - Canada
Since no water left the containter, if you add a 5 pound boat to the container of water, it will now weight 5 pounds more, whether the boat floats or not.
February 25, 2006
If you place a tub of water on a scale and it weighs 1,000lbs., would the weight of that tub of water increase if you get in the tub of water and float. No water spills over the edge thus keeping the amound of water in the tub consistent.
David - USA
The weight would be the sum of the person, tub and water, whether the person floated or not. The floating only has to do with the density of the object compared to the density of the water.
Of course, it water spilled out for an object that floated, then the weight would remain at 1000 lbs.
February 19, 2006
hi I just wanted to comment on this article because I am doing a Density project related to this topic. I just wanted to ask, is cooking oil more dense than water and salty water?
Emily - USA
Typcially, cooking oil will float in water, thus making it less dense. Salty water is more dense than pure water.
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