Drawing Free-body Diagrams Worksheet Answers
Newton's laws
Isaac Newton's laws surrounding forces were formulated hundreds of years ago, but are still used today - they help to describe the relationship between a body and the forces that act upon it.
Free body diagrams and vector diagrams - Higher
Free body diagrams are used to describe situations where several forces act on an object. Vector diagrams are used to resolve (break down) a single force into two forces acting at right angles to each other.
Free body diagrams
A free body diagram 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:
Weight, reaction force and friction for an object moving at constant speed down a hill:
Weight, upthrust, thrust and air resistance for an accelerating speedboat:
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A box is at rest on a table. Draw the free body diagram for this situation.
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A trolley is being pulled along a rough surface at a constant speed. Draw the free body diagram for this situation.
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Vector diagrams
The resultant vector for two vectors at right angles to each other can be worked out using a scale diagram, or using a calculation.
Using a scale diagram
In the diagram below, two velocities are at right angles to each other. One is 4 m/s and the other is 3 m/s.
If the diagram is drawn to scale like this, the magnitude of the resultant vector can be found by measuring the length of the diagonal vector arrow.
Pythagoras' theorem can be used to calculate the resultant vector.
In any right-angled triangle, the square of the longest side is the sum of the squares of the other two sides. This can be written in the formula:
a 2 + b 2 = c 2
This is where c is the longest side.
In the example above, a = 4 m/s and b = 3 m/s.
c 2 = 4 2 + 3 2
c 2 = 16 + 9 = 25
\[c = \sqrt{25}\]
\[c = 5~m/s\]
Here, c is equal to the line marked 5 m/s, as both dissect the rectangle in the same way.
Drawing Free-body Diagrams Worksheet Answers
Source: https://www.bbc.co.uk/bitesize/guides/z9s92nb/revision/3
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