Calculating Forces

Use scale drawings to find resultant forces

• Draw all the forces acting on an object, to scale, ‘tip-to-tail’

• Then draw a straight line from the start of the first force to the end of the last force-this is the resultant force

• Measure the length of the resultant force on the diagram to find the magnitude and the angle to find the direction of the force

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An object is in equilibrium if the forces on it are balanced

• If all of the forces acting on an object combine to give a resultant force of zero, the object is in equilibrium
• On a scale diagram, this means that the tip of the last force you draw should end where the tail of the first force you draw begins
• You might be given forces acting on an object and told to find a missing force, given that the object is in equilibrium. To do this, draw out the forces you do know, join the end of the last force to the start of the first force. This line is the missing force so you can measure its size and direction

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You can split a force into components

• Not all forces act horizontally or vertically-some act at awkward angles
• To make these easier to deal with, they can be split into two components at right angles to each other
• Acting together, these components have the same effect as the single force
• You can resolve a force by drawing it on a scale grid. Draw the force to scale, and then add it horizontal and vertical components along the grid lines. Then you can just measure them

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