Resultant Forces and Work Dones

Free body diagrams show all the forces acting on an object

• Size of the line shows the relative magnitudes
• Need to be able to describe all forces happening on something

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A resultant force is the overall force on a point or object

• In most situations there are at least 2 forces acting on an object
• If you have a number of forces acting at a single point, you can replace them with a single force
• This single force is called the resultant force
• If the forces all act along the same line, the overall effects is found by adding those going in the same direction and subtracting any going in the opposite direction

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If a resultant force moves an object, work is done

• To make something move a force must be applied
• The thing applying the force needs a source of energy
• The force does work to move the object and energy is transferred from one store to another
• Whether energy is transferred usefully or is wasted you can still say that work is done
• You can find out how much work has been done using: W=Fs
• One joule of work is done when a force of one newton causes an object to move a distance of one metre. You need to be able to convert joules to newton metres:1J=1Nm

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