# Force Facts

• A force is a push or a pull. It can make something start to move, slow down or speed up, change direction or change shape or size. The greater a force, the more effect it has.
• The wind is a force. Biting, twisting, stretching, lifting and many other actions are also forces. Every time something happens, a force is involved.
• Force is measured in newtons (N). One newton is the force needed to speed up a mass of one kilogram by one meter per second every second.
• When something moves there are usually several forces involved. When you throw a ball, the force of your throw hurls it forwards, the force of gravity pulls it down and the force of air resistance slows it down.
• The direction and speed of movement depend on the combined effect of all the forces involved — this is called the resultant.
• A force has magnitude (size) and works in a particular direction.
• A force can be drawn on a diagram as an arrow called a vector (see vectors). The arrow’s direction shows the force’s direction. Its length shows the force’s strength.
• Four fundamental forces operate throughout the Universe: gravity, electric and magnetic forces (together called electromagnetic force), and strong and weak nuclear forces (see nuclear energy).
• A force field is the area over which a force has an effect. The field is strongest closest to the source and gets weaker farther away.
• Every force acts in a straight line. Things move round because of a ‘turning effect.
• A turning effect is a force applied to an object that is fixed or pivots in another place, called the fulcrum.
• In a door the fulcrum is the hinge.
• The size of a turning force is known as the moment. Load
• The farther from the fulcrum that a force is applied, the bigger the moment is.
• A lever makes it much easier to move a load by making use of the moment (size of turning force).
• A first-class lever, such as pliers or scissors, has the fulcrum between the effort and the load; a second-class lever, such as a screwdriver or a wheelbarrow, has the load between the effort and the fulcrum; a third-class lever, such as your lower arm or tweezers, has the effort between the load and the fulcrum.
• Gears are sets of wheels of different sizes that turn together. They make it easier to cycle uphill, or for a car to accelerate from a standstill, by spreading the effort over a greater distance.
• The gear ratio is the number of times that the wheel doing the driving turns the wheel being driven.
• The larger the gear ratio the more the turning force is increased, but the slower the driven wheel turns.