Floating and sinking

Folio Content

This focus idea is explored through:

  • Contrasting pupil and scientific views
  • Critical teaching ideas
  • Teaching activities

Contrasting student and scientific views

Three students are experimenting with floating film canisters.Students accept frequent experiences with objects floating and sinking in the bathroom, in a pond pool or at the embankment. They form understandings from an early historic period about these ideas and every bit chiefly the words used to describe them.

Students tend to pay little attention to why things float or sink and may perform simple tests on objects in a tank of water without whatever understanding of the forces involved in why they float or sink. These can be quite challenging to identify and sympathize.

Students normally believe that:

  • heavy objects sink and light objects float regardless of their size, shape or the type of material used to make them
  • a true floating object must be wholly above the surface of the liquid
  • all objects that float must contain some trapped air and that is the only reason why they bladder
  • the amount of liquid on which the object floats matters somehow, i.eastward. an object volition float college in a larger volume or deeper liquid.

Research: Biddulph & Osborne (1984), Mitchell & Keast (2004)

Scientific view

An object floats when the weight force on the object is balanced by the upward push of the water on the object. The upwards push of the water increases with the book of the object that is under water; it is not affected by the depth of the water or the corporeality of water.

If the weight force down is larger than the upwardly button of the water on the object then the object will sink. If the contrary is truthful then the object will ascent – ascension 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 button of the water steadily increases until it is in residue with the weight force of the object, and the object and then continues floating at this level with the two forces in residual.

Many objects that are hollow (and so generally contain air) bladder because the hollow sections increase the volume of the object (and then the upwards push button) for very picayune increase in weight force down. However, it is not necessary for an object to contain air in order to float.

No object can float without some part of it being beneath the surface of the h2o.

Critical instruction ideas

  • To float, the weight strength on an object must be balanced by the upward push by the h2o on the object.
  • The amount of material and the blazon of cloth that makes up the object affects the size of the weight force on the object.
  • The volume of the object, which can often exist altered by changing the shape, will affect the size of the upward push button on the object.

Explore the relationships between ideas almost floating and sinking in the Concept Development Maps: Laws of Motion

Students will exist familiar with the idea that objects have weight and that the size of the weight force is determined past the blazon 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 up on the object. For case, when yous try to push a surfboard under the water you can feel the h2o pushing the lath up. Objects such equally rocks that have sunk, are nevertheless experiencing an upwards push; it is merely not as potent as the weight force.

Students should exist encouraged to view floating equally existence a result of the balance of the weight force on an object and the upwardly push button of the water on the submerged part of the object.

Students should be guided to recognise that changing the shape of an object:

  • does non change the weight of the object
  • can alter the volume of the object.

Research: Carr, Barker, Bell, Biddulph, Jones, Kirkwood, Pearson & Symington (1994)

Teaching activities

Provide an open up trouble for students to explore via play

Line drawing shows a no. of resealable film containers which are floatingAt this level it is appropriate for students to experiment with a diverseness of objects to see if they float or sink in water. They should be encouraged to identify common characteristics of objects that bladder and those that sink. Students can endeavour submerging a ball in a saucepan 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 dissimilar objects to see whether that affects how they float or sink in h2o. Students could experiment with different sized objects with the same weight to encounter how this influences their floating.

Encourage students to experiment with fiddling sealable containers such as empty film containers to come across if they float, and to what level, in h2o. They tin can then experiment past putting dissimilar amounts of sand into the containers to see how the change in weight affects the level of their floating.

Do using and build the perceived usefulness of a scientific model or idea

The students could also model being an engineer by designing a submarine (out of a plastic drinkable bottle) to retrieve a sunken treasure. Introducing more sand into the bottle will increase the weight of the bottle and and then increase its weight force resulting in it floating lower in the water. When the weight strength is greater than the upward push of the h2o on the 'submarine' (canteen) then the 'submarine' will sink to recover the treasure.

Clarify and consolidate ideas for/past the communication to others

Have students modify the shape of a lump of plasticine (or 'Blu-tack') to encounter if they can make it float in h2o. This tin can pb to a discussion about why all boats don't need to be made of forest or inflatable plastic, and a heavy metal, physical or fibreglass transport can bladder on h2o just as successfully.

Scientists are curious and students can model beingness a scientist past exploring things that can affect whether an object floats such as its shape, weight or the amount or blazon of liquid used to float it. This investigations are a perfect opportunity for students to develop experimenting and reporting skills.

Practise using and build the perceived usefulness of a scientific model or idea

An example of an agreeable story designed to focus on the concepts of floating and sinking is 'Who sank the boat?' written by Pamela Allen. This story could provide opportunities for students to heighten further questions near floating and sinking.

Research: Allen (nineteen​88)