The upwards push of the water increases with the volume of the object that is under water; it is not affected by the depth of the water or the amount of water. If the weight force down is larger than the upward push of the water on the object then the object will sink.
If the reverse is true then the object will rise — rising is the opposite of sinking. Different objects float at different levels in the water because as most regular objects are lowered into the surface of water, the upward push of the water steadily increases until it is in balance with the weight force of the object, and the object then continues floating at this level with the two forces in balance. Many objects that are hollow and so generally contain air float because the hollow sections increase the volume of the object and so the upwards push for very little increase in weight force down.
However, it is not necessary for an object to contain air in order to float. Explore the relationships between ideas about floating and sinking in the Concept Development Maps : Laws of Motion. Students will be familiar with the idea that objects have weight and that the size of the weight force is determined by the type of material and how much of it is used to make up the object.
Students should learn that when an object floats the water is pushing upwards on the object. Do you know what density means? Well everything around us is made up of tiny molecules. In some objects these molecules are jam packed together, and in others they are loosely packed together. This is actually what density means. How does this sink and float work? Some boats are massive, and would seem very dense, so how do they stay afloat? Now comes buoyancy, which is the opposite of gravity.
But what is buoyancy? Think about what happens when you put an ice cube into a glass of water. As the ice cube displaces moves some of the water to make way for itself, the water level rises and the ice floats partially in and out of the water.
If the weight of the object is bigger than the buoyancy, the object will sink to the bottom. If the buoyancy is bigger than the weight, the object will float. Some liquids, like oil, create less buoyancy than water, so objects that float in water will sink in oil. Other liquids, like syrup, create more buoyancy than water, so objects that sink in water will float in syrup.
A substance called graphene aerogel is the lightest solid ever invented. A block the size of a brick weighs less than a grain of rice and can float on a puff of air. Science Sparks Wild Sparks Enterprises Ltd are not liable for the actions of activity of any person who uses the information in this resource or in any of the suggested further resources. Science Sparks assume no liability with regard to injuries or damage to property that may occur as a result of using the information and carrying out the practical activities contained in this resource or in any of the suggested further resources.
These activities are designed to be carried out by children working with a parent, guardian or other appropriate adult. The adult involved is fully responsible for ensuring that the activities are carried out safely. Your email address will not be published. Why do things float in water? Do the balls which float all have something in common? Are they hollow? Test each ball to see if your predictions are correct. Take a ball which sank to the bottom of your container and wrap in bubble wrap.
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