As the water is heated, the molecules move faster and a little further apart. The circles represent water molecules. The molecules are randomly arranged. They interact with each other because of their ...

The circles in this drawing represent water molecules. They are not in any exact order but are near each other because of their attractions. The motion lines near some of the circles show that the ...

Listen to the full series on BBC Sounds. When people walk, run, or travel in a car, their speed will change. They may speed up, slow down or pause for traffic. The speed at which a person can walk ...