**(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

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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