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(New tips are continually added to these pages.  Check back in a few months' time for more)

TOPIC 3:     Forces and Moments

Tip 1:

Every student knows F = ma.   But what's F?

F is the Resultant Force, or Net Force.

For example, if I push a 5 kg box with a force of 30 N to the right, and you push the same box with a force of 20 N to the left, then the Resultant Force is 10 N to the right (I win).

The box will then accelerate towards the right at 2 m s-2, assuming that friction and air resistance are negligible.

 

Tip 2:

The moment of a force about a pivot is defined as the product of the force F and the perpendicular distance d from the line of action of the force to the pivot.

Many students just remember Moment = Force x Distance, when in fact the most important key words are perpendicular distance and line of action.

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Since "O" level problems are relatively simple, most of the time you will get the right answer just by using the formula Moment = Force x Distance, but do keep the above diagram in mind, especially when you proceed to the "A" levels.

 

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