Y E A R 3

• Things move because of forces. Forces can be either a push or a pull.
• Objects move differently on different surfaces. This is because when two objects come into contact with each other there is something called friction. Friction can sometimes be useful and sometimes not.
• We are not always able to see forces with our eyes. For example, magnets can pull and push. Magnets have poles: north poles and south poles. We call it attraction when magnets pull, and repelling when magnets push. Some materials are not affected by magnets.

Y E A R 5

• Forces cause movement. A change in a force causes a change in movement.
• There is a force called gravity which attracts objects to each other. The size of the attraction depends on the mass of the object. We experience gravity on Earth as the force that keeps us on its surface. Gravity is weaker on the moon and stronger on planets with a greater mass.
• The effect of gravity can also be seen with the tides. The Moon's gravitational pull moves water on Earth's surface.
• Friction exists between objects moving through the air and the particles of air. This is called air resistance. The shape and size of an object affects how much air resistance there is.
• Friction exists between objects moving through water and water particles. This is called water resistance. The shape and size of an object affects how much air resistance there is.
• Objects float in on liquid because the forces acting on them are equal. We call these forces upthrust and weight. When the forces are unequal, objects sink. This concept is called buoyancy. This is unrelated to mass.
• A small force can sometimes cause a greater force. This is called a mechanism. Examples of mechanisms that do this are gears, levers and pulleys.