Water resistance is a type of friction force which acts between a liquid and the surface of an object. It acts to slow down or stop objects that are moving through liquid.
This force acts in the opposite direction to the object moving through the liquid.
A boat travelling through water encountering water resistance
Objects experience a different amount of water resistance, depending on their size and shape.
The larger the object, the more water resistance it will experience.
Some shapes are more streamlined than others. This means that the object has a smooth contour or outline, so it can travel through the water more easily as it encounters less water resistance.
As well as affecting objects like boats that move horizontally through the water, water resistance can affect objects moving down through water, i.e. an object sinking. Gravity pulls the object down towards the Earth's surface, but water resistance acts in the opposite direction, slowing down the sinking object. The more streamlined the object is, the faster it will sink, as it is less affected by water resistance.
Gravity and water resistance exerting opposite forces on an object sinking in water
According to the National Curriculum objectives for Science, children learn about water resistance in KS2. It is assigned as compulsory learning in Year 5 under the 'Forces' strand of learning.
The non-statutory guidance suggests that pupils might explore resistance in water by making and testing boats of different shapes.
