Work, Force and Energy Notes

TYPES OF FORCES

•      Forces are acting everywhere in the universe at all times.

•      There are different types of forces.

Gravitational force (Gravity):

•      Gravity or gravitational force is the force that attracts objects to the centre of the Earth.

•      Gravity is a key force in the universe, and it is the force which brought our planet into existence.

•      Gravity is one of the simplest forces, and it can be illustrated through the classic story of Sir Isaac Newton and his apple.

FRICTION

•      Friction is a force that slows down moving things.

•      Friction is what happens when any two things rub against each other.

•      These can be solid things, like our two hands rubbing together, or our skis rubbing on the snow, or a hammer hitting a nail, or they can be gases, like friction with the air slowing down our car, or liquids, like friction with the water slowing down a boat.

•      Friction happens when the rough edges of one object snag on the rough edges of another object, and some of the object’s energy has to be used to break off those rough edges so the objects can keep moving.

•      And when we rub two soft things together, like our hands, sometimes they squish into each other and get in each other's way.

•      But even completely smooth, hard things have some friction. This friction is the result of the molecules in both objects being attracted to each other.

ADVANTAGES OF FRICTION

1. When we walk, we are actually pushing ourselves backwards on the ground with our feet.

•      Friction between our feet and the ground stops us from slipping backwards. Thus, friction makes it possible for us to walk.

•      We find it hard to walk on ice or on smooth, polished floor as movement across these surfaces produce less friction. That is why; we often slip on icy ground or wet floor.

2. The friction between the tyres of vehicles and the road makes them roll forward. Thus, friction makes movement of vehicles possible.