Forces are responsible for interactions between objects; gravity being one of the most important. An object with mass in a gravitational field experiences a force known as weight.

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Two forces can be added together to find a resultant force. A single force can be resolved (broken down) into two component forces at right angles to each other.

In the diagram of a toy trailer below, when a child pulls on the handle, some of the 5 newton (N) force pulls the trailer upwards away from the ground and some of the force pulls it to the right.

A force can be represented by a vector quantity that has both magnitude and direction. Vector diagrams can be used to resolve the pulling force into a horizontal component acting to the right, and a vertical component acting upwards.

Draw a right-angled triangle to scale, in which each side represents a force. Try to choose a simple scale, for example 1 cm = 1 N. For the toy trailer example above, draw:

- a line representing the 5 N force at 37°
- a horizontal line ending directly below the end of the first line
- a vertical line between ends of the two lines
- arrow heads to show the direction in which each force acts

Measure the lengths of the horizontal and vertical lines. Use the scale for the first line to convert these lengths to the corresponding forces.

An alternative way of drawing the resolved forces is shown here. The effect of the child's pulling force can be achieved exactly the same by pulling horizontally and vertically. The two component forces together have the same effect as the single force.