# Identifying and Representing Forces

## Identifying Forces

• Force is a push or pull that causes an object to move, stop moving, or change direction.
• It is important to identify all the forces in a particular situation. These forces can be obvious ones, such as gravity or friction, but be sure to not to overlook hidden forces such as air resistance or tension in a string.
• When calculating, ensure to take into account the magnitude and the direction of a force. Both of these components are essential in correctly applying forces.

## Representing Forces

• Understand how to use a force diagram to represent the forces acting on an object. These diagrams are sometimes also called Free-Body Diagrams or FBDs.
• When drawing a force diagram, you will most likely be representing the forces acting on a single object—think of the object as isolated or “free” from its environment.
• In a force diagram, each force is represented by an arrow. The direction of the arrow shows the direction of the force and the length of the arrow represents the magnitude of the force.
• Scale is essential when drawing force diagrams. All forces should be represented in proportion. For example, if one force is twice as large as another, its arrow should be twice as long.
• Forces are vector quantities, meaning they have a direction and magnitude. When adding forces, remember to take into account the vector nature of forces. This often involves using trigonometry and the principles of vector addition.

## Types of Forces

• Gravity: This is the force that pulls objects towards each other. It acts downwards towards the centre of the earth.
• Tension: This is the force that is transmitted through a string, rope, cable or wire when it is pulled tight by forces acting from opposite ends.
• Friction: This is the force that resists the movement of solid surfaces, fluid layers, and material elements sliding against each other.
• Air resistance or Drag: This is the force that is caused by air, acting opposite to the direction of motion when an object is moving.
• Normal force or Contact force: This is the force exerted by a surface that supports the weight of an object resting on it. It acts perpendicular to the surface.
• Applied force: This is an additional force that is applied to an object, such as pushing a book across a table.