What makes objects sink

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. For example, when you try to push a surfboard under the water you can feel the water pushing the board up.

Objects such as rocks that have sunk, are still experiencing an upwards push; it is just not as strong as the weight force. Students should be encouraged to view floating as being a result of the balance of the weight force on an object and the upward push of the water on the submerged part of the object.

At this level it is appropriate for students to experiment with a variety of objects to see if they float or sink in water. They should be encouraged to identify common characteristics of objects that float and those that sink. Students can try submerging a ball in a bucket of water in order to feel the upward push of the water on the ball.

A more quantitative approach could involve measuring the weight of different objects to see whether that affects how they float or sink in water. For 6 Resources. Curated resources with practical work that students can complete at home, or that teachers can use when giving demonstrations Remote teaching support One piece of foil will sink and the other will float.

The piece of foil scrunched above water traps some of the air, which Enrichment Activity Food colouring and oil don't mix, and as the two separate the food colouring sinks into the water, leaving trails of colours. Other resources on Density Density Properties of Matter. Density Properties of Matter.

Misconceptions Properties of Matter Some students think that heavy objects sink and light object float regardless of shape and size Number of Resources 0 Number of References 2 Number of Diagnostic Resources 2.

We've won an award! Learn more. Volume is the amount of space that an object takes up in three dimensions. If we take the same volume one cubic centimetre of foam, wood and concrete, we can see that each has a different mass. Less Dense, More Dense If something is heavy for its size, it has a high density. If an object is light for its size it has a low density.

Imagine a big bowl of popcorn, compared to a big bowl of pebbles, which would feel heavier? It is easy to estimate relative densities if you keep either the volume or the mass of two objects the same. If you filled one bag with a kg of feathers and another with a kg of lead you would see that the feathers take up much more room, even though both bags have the same mass.

This because feathers are less dense, they have less mass per volume. If you made a copper cube and an aluminum cube of the same volume and placed one in each hand, you would be able to feel that the copper cube would be heavier. Copper has more mass per volume than aluminum. How can one substance have more mass per volume than another? There are a few possibilities:. Any one or a combination of these explanations could be the reason why one substance has a higher density than another.

In the case of copper and aluminum, their atoms are arranged similarly, but copper atoms are smaller and have more mass than aluminum atoms, giving it a higher density.

Density, Sinking and Floating Why do some things float, while others sink? You might expect heavier objects to sink and lighter ones to float, but sometimes the opposite is true.

The relative densities of an object and the liquid it is placed in determine whether that object will sink or float. You can really see relative densities at work when you look at a heavy object floating and a lighter one sinking. For example, imagine putting a small piece of clay and a large, heavy wax candle in a tub of water. Sinking and floating applies to liquids too. For example, if you add vegetable oil to water, the oil floats on top of the water because the oil has a lower density than the water.

The water pushes upward against the object with a force buoyancy equal to the weight of water that is displaced. When the ball is submerged in the water, it displaces its volume in water.

However, the weight of the ball is more like 55 N. A beach ball may have the same volume as a bowling ball, but it has a much smaller mass. When you a beach ball in a tub of water, it displaces the mass of water equal to its own mass—about 0.