Does Rubbish Float or Sink?

Ocean pollution is a serious problem that affects marine life and the health of our oceans. It is caused by human activities such as littering, dumping waste into the ocean, and oil spills. Ocean pollution harms animals by entangling them in plastic debris or exposing them to toxic chemicals. It also damages entire ecosystems like coral reefs and estuaries. We can reduce our impact on the ocean environment by reducing plastic use, properly disposing of rubbish, supporting eco-friendly products, and properly disposing of hazardous waste.

Students can be made aware of the problems associated with ocean and water pollution by firstly investigating whether items of rubbish float, do not float or sink in water and then looking at the impact of litter on marine life.

Skills of questioning, observing, predicting, investigating, experimenting, estimating, measuring, analysing, recording and communicating will be taught.

It is important to investigate whether different types of litter will float, will not float or will sink as this information will help students understand that each type of litter can have a different impact on how marine life will be affected by the litter. For example, sea birds may try to eat rubbish that floats. Turtles, fish and sea creatures may get tangled in rubbish that floats or partially floats. Fish and other sea creatures may eat rubbish that has sunk to the bottom of the ocean.

Litter that floats may be more easily collected when cleaning areas of polluted ocean. Beach clean-ups, floating nets for gathering rubbish and river interceptors, mesh fences and bubble barriers are all methods of picking floating rubbish from our waterways. ¹

Here you can download the worksheet and the vocabulary card for this experiment.

• worksheet as pdf and docx file
• vocabulary card as pdf and docx file

Items will float, will partially float or will sink in water. The size, shape and makeup of the material, along with the salinity of the water, will determine whether each item floats or sinks.

Objects float or sink based on their density relative to the fluid in which they are placed. If an object's density is lower than the fluid, it floats; if the object’s density is higher than the fluid, it sinks. Shapes with a large surface area and low density, like flat, wide objects, tend to float better, while compact, dense shapes are more likely to sink. Materials like wood and foam typically float because they are less dense than water, while metals sink because they are denser.

For an object to partially float, its density must be close to that of the liquid it's in, or its shape must be designed to displace enough liquid to support part of its weight while allowing the rest to be submerged. The salinity of water increases its density, which can cause an item to float more easily, partially float, or sink less readily compared to in freshwater.

Items of rubbish can be chosen according to the age and understanding level of the students. Fewer items or more readily available items can be chosen for younger or less well able students.

Easier

This experiment can be made simpler by providing cards with the pictures of objects to be tested for floating or sinking. After the experiment the children can sort these cards into objects that float, that sink to the bottom, or that neither float on the top nor sink to the bottom.

More challenging

Students can discuss other items that are commonly found in waterways. These objects can also be tested. Many items that float or sink can be physically changed in some way leading to a different outcome. For example, a metal soda can may float if it has no solids or liquids inside but may sink if full of water or sand. Students can be encouraged to physically try and change the items tested for a different outcome.

Students can record their results in a graph or table.

Students can make their own video recording of their experimentation, or to present their findings to other students in the school.

Adding salt to the water will affect the salinity of the water, thereby affecting the density of the water. This in turn will affect how items will float or sink in water. Salinity describes how much salt is dissolved in a sample of water. The more salt that is dissolved in the water sample, the greater its salinity. If you compare two samples of water which have the same volume, the sample with the higher salinity will have greater mass and it will therefore be more dense. Repeat the experiment above adding varying amounts of salt to the water. Will this affect which items of rubbish will float or sink? Relate this to our nature; our oceans are salty but rivers, lakes and inland waterways are not salty.

Working for healthy water bodies

Hydrologist
Hydrologists specialize in the study of water resources. They analyse the distribution, movement, and quality of water in the Earth's atmosphere and on its surface.

• Learn more about hydrologists

Water quality analyst
Water quality analysts assess and monitor the quality of water in various settings, such as rivers, lakes, and water treatment facilities. They ensure that water sources are safe and clean for human use.

Water resource manager
Water resource managers are responsible for overseeing the sustainable use and conservation of water resources at a waterworks. They work to ensure the efficient use of water for agriculture, industry, and municipal purposes.
 

Working for the environment

Climate scientist
Climate scientists study long-term patterns in weather and climate, and they investigate how climate change impacts the Earth's hydrological cycle.

Environmental engineer
Environmental engineers design solutions to environmental problems, such as water treatment systems and pollution control technologies. They play a crucial role in ensuring water quality and sustainability.

Environmental scientist
Environmental scientists study the natural world and its ecosystems. They work to understand and solve environmental issues, such as water quality and sustainability. This experiment provides a foundation for those interested in environmental science careers.

• Learn more about environmental scientists