!#8# Cohesion and adhesion - Two activities for primary school teachers

!±8± Cohesion and adhesion - Two activities for primary school teachers

Here are two simple activities to show students the basic concepts of cohesion and adhesion.

COHESION

"Niagara Falls"

MATERIALS

A Penny
Pipette
Detergent

PROCEDURE

Ask: "How many drops of water you think you can drop a dime on this site without it over the edge?" Put the pot cent on a smooth surface. Pipette with the drops of liquid onto a dime down at a time, counting the drops until the oil spillEdge.

Take the same coin, and rub a solvent.

Predicting the number of drops of water that you can put on the dime now, without it pouring over the edge.

With the pipette, the liquid drips down to the penny drops and counting.

STATEMENT

Water molecules have a strong cohesion, or attraction to other water molecules. The unifying force of the molecules is like the skin as a liquid surface, called surface tension. Soap reduces the surface tension, soto stay a few drops on the penny with soap.

MEMBERSHIP

"PASS THE PEPPER"

MATERIALS

Cereal Bowl
Pepper
Liquid detergent for dishwashers

PROCEDURE

Fill bowl with water and brush a little pepper on top.

Ask: "What do you think will happen to the pepper, if we add Detergent?"

Drop a few drops of detergent to the center of the bowl.

STATEMENT

Adhesion is the attractive force that holds together the molecular ANDERS bodies in contact. TheWater is hands pepper evenly from all directions. The detergent reduces the adhesive force between the liquid and pepper. The fluid around the edges of the basin, influenced by the detergent industry, still has its pulling power.