We probably already know that some things will float in water and some will not. Do you know why? Sometimes the best way to find out if something will sink or float is just to try it.
Buoyant Force is a force that arises when an object displaces a fluid in a force field. The fluid can be a liquid, as in the case of a boat floating on a lake, or the fluid can be a gas, as in a helium-filled balloon floating in the atmosphere.
There are three kinds of buoyancy:
- Positive buoyancy, where something floats on top of a liquid
- Neutral buoyancy, where something just stays in the middle of the liquid because it has the same density as the liquid (e.g. fish)
- Negative buoyancy, where something sinks to the bottom
Examples:
- a ping pong ball (or anything else made of plastic) floating on water.
- oil floating on top of vinegar in a salad dressing
- a submarine rising to the surface when it adds air to its inner compartments
Whether an item sinks or floats in water depends on two main factors -- weight and density. For example, boats float, but in certain circumstances, even a boat with no leaks can easily sink if it weighs too much relative to its size.
Weight
- An object floats if its weight is lighter than the amount of water that is being pushed out from beneath it. Heavier objects will sink because the water weighs less than the object sitting on top of it.
Density
- Density refers to the overall compactness of the item. For example, if you have two objects that are the same weight, but are different sizes, one may sink and the other might not. If one object has a large surface area, that object has a greater ability to push the water out from underneath and float.D = m / v
Resources:
http://www.ehow.com/facts_8027331_do-things-sink-water.html
http://www.askaboutireland.ie/learning-zone/primary-students/3rd-+-4th-class/science/floating-and-sinking/floating-and-sinking-1/
http://www.ehow.com/facts_8027331_do-things-sink-water.html http://precast.org/2010/07/why-buoyancy-forces-cannot-be-ignored/
http://physics.wsu.edu/academics/labs/201Labs/15_Buoyancy(2006-05-31).pdf
http://ca.answers.yahoo.com/question/index?qid=20080223215114AAmXyWO
