Possible Difficult Concepts

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‘Air Resistance’ gets in the way of Galileo’s theory. Smaller light objects like a feather or a piece of paper may travel slower to the ground than a heavier object like a stone, because of another force called Air Resistance.   Where there is no air resistance all objects fall at the same speed.   (Galileo’s famous experiment). This was proved in a vacuum tube by Irish scientist Robert Boyle, and on the moon (where there is no air) by astronaut David Scott.

Children sometimes conclude incorrectly that gravity does not work through water, when they see things floating in water, or see that things hanging from a spring balance weigh less in water.   The reason that they float or weigh less is because of the upthrust (buoyancy, pushing-up force) of water   (See ‘Sinking and Floating’ unit).

The distinction between ‘Mass’ and ‘Weight’ can cause confusion for teachers and children.  Most people talk about their weight being measured in kilograms, where in fact, strictly speaking, weight being a force should be measured in Newtons . (See the section on ‘Weighing things’ for clarification on this.   This   really only needs to be touched on very briefly in Sixth Class – it is more for second level children and a very brief introduction is adequate here.).