Free body diagrams
A A simplified drawing of an object or system showing the forces acting on it. The forces are shown acting away from the centre of a box or dot. models the forces acting on an object. The object or 'body' is usually shown as a box or a dot. The forces are shown as thin arrows pointing away from the centre of the box or dot.
Free body diagrams do not need to be drawn to scale but it can sometimes be useful if they are. It is important to label each arrow to show the magnitude of the force it represents. The type of force involved may also be shown.
Examples of free body diagrams:
Weight and reaction force for a resting object
Drawing of situation
Free body diagram
Weight, upthrust, thrust and air resistance for an accelerating speedboat
Drawing of situation
Free body diagram
Resultant forces
An object may have several different forces acting on it, which can have different strengths and directions. But they can be added together to give the The single force that could replace all the forces acting on an object, found by adding these together. If all the forces are balanced, the resultant force is zero.. This is a single force that has the same effect on the object as all the individual forces acting together.