Why does objects sink

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. Students could experiment with different sized objects with the same weight to see how this influences their floating. For 6 Resources.

Demonstration: This rough method can produce a difference of mass of at least 8 g. With enough apparatus it could be done as Practical Activity This activity allows pupils to make some measurements to measure the density of a material for themselves.

Classroom Activity Other resources on Density Density Properties of Matter. Density Forces and Motion. Density Properties of Matter. We made out superhero arm bands and a raft,. Rainy Day Mum has a lovely activity using boats made from pie tins. Try a p irate themed sink and float investigation. Find out how many coins it takes to sink a foil boat. Learn about density with this easy investigation, can you find something to float on each layer?

Instead of making an object less dense by adding bubble wrap, try changing the density of water to help an object float. 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.

Then, place the clay and candle in a clear container of water. Carefully pour water into the empty metal container until it fills the container to the same level as the candle in the other container. You may use a dropper to add the last bit of water and prevent spilling. The goal is to compare the mass of equal volumes of wax and water. The water has a greater mass than an equal volume of wax. So, the density of water must be greater than the density of wax.

If students have trouble understanding this relationship between the mass and density of equal volumes, have them think about the demonstration from Chapter 3, Lesson 1 with the aluminum and copper cubes.

Both had the same volume, but the copper cube weighed more. Because the copper had more mass, it also had a greater density. The clay has a greater mass than an equal volume of water. So, the density of clay is greater than the density of water. Wax is made of carbon and hydrogen atoms connected together in long chains. These long chains are tangled and intertwined and packed together to make the wax. Even though they both have lots of hydrogen atoms, water is more dense than wax because the oxygen in water is heavier and smaller than the carbon in the wax.

Also, the long chains of the wax do not pack as efficiently as the small water molecules. Clay has oxygen atoms like water, but it also has heavier atoms like silicon and aluminum.

The oxygen atoms are bonded to the silicon and aluminum to make molecules with a lot of mass. These are packed closely together, which makes the clay more dense than water. Students should realize that if an object weighs more than an equal volume of water, it is more dense and will sink, and if it weighs less than an equal volume of water, it is less dense and will float. Predict whether the following objects will sink or float. Read more about sinking and floating in the teacher background section.

Note : Students may wonder why boats made out of dense material like steel can be made to float. This is a good question and there are several ways of answering it. A key to understanding this phenomenon is that the density of the material and the density of an object made of that material are not necessarily the same.