MYP+Turning+Effect+of+Forces

**Experiment**

 * Aim: To verify the principle of moments**

uniform metre rule, various weights W1 and W2, cotton loops, knife edge retort stand
 * Apparatus:**

1. Set up the apparatus as shown on the board with the knife edge at the 50 cm mark 2. Hang W1 =0.5 N and W2 = 0.4 N on opposite sides of the pivot with the cotton loops. 3. Balance the system by adjusting the distances d1 and d2. Record the values of d1 and d2. 4. Repeat the experimentfor another three sets of W1 and W2 as shown in the result table. 5. Record the corresponding values of d1 and d2. 6. Find the relationship between weights and the distances from the result table.
 * Method**


 * Results**
 * W1[N] || d[cm] || W2[N] || d[cm] || **Relationship** between forces and the distances ||
 * 0.5 ||  || 0.4 ||   ||   ||
 * 0.4 ||  || 0.6 ||   ||   ||
 * 0.4 ||  || 0.8 ||   ||   ||
 * 0.5 ||  || 0.6 ||   ||   ||

What do we observe about the values in the result table? What relationship between weights and the distances from the pivot can we find from the values?
 * Questions for analysis;**

**=> Principal of Moments**
When a body is in __ equilibrium __, the sum of clockwise moments about a pivot __ is equal to __ the sum of anticlockwise moments about the same pivot.

The results show that, in every row, the anticlockwise turning force about the pivot (W1 x d1) is __ equal __ to the clockwise turning force about the pivot (W2 x d2). This is the P__ rinciple __ of M__ oments __. This indicates that when an object is not turning, the clockwise and anticlockwise moments acting on it are __ balanced __; which means the __ resultant __ moment is __ zero __.
 * Conclusion:**

Moments
The __ moment __, the turning effect of a force, also known as __torgue__ is the product of the __ force __ and the perpendicular __ distance __ from the pivot to the line of action of the force.

Moment of a force = __ //F// x //d// __ where //F//= force [in N] and //d// = perpendicular distance from pivot [in m]

The SI unit of the moment of a force is the__ newton metre __ [__ N m __]. The moment of a force describes with __ magnitude __ in N m and __ direction __ as clockwise or anticlockwise.

**Usages for moments;** Read text page 89 and show some examples.
A student conducts the following experiment on a half-metre rule to feel the turning effect of a force (a) If the weight W is placed at the 15cm mark to the left from 0 cm mark, find the moment of the force applied by a hand when holding the ruler horizontally at the position between 40 cm and 50 cm to the far left.
 * Question A**

(b) He then shitrs the same weight W to the 5 cm mark and finds that it is more difficult now to maintain the half-metre rule in a horizontal position than before in (a). Why is this so?

Take notes on centre of mass and stability after reading text page 41 - 43. Do questions on the text p. 43 and 44.
 * Homework**