Triangular block for pivot
Masses (100g, 10g)
Place the ruler on the pivot so that the pivot is under the 30cm mark. Do not alter this.
Place a fixed mass (e.g. 300g) on the end of the short side of the ruler to provide a fixed load (in this case 3N). Do not alter this either. Tape may be needed to fix this in place.
At the other end of the ruler start adding masses until the short end just lifts. Record the mass needed to make it lift and record the force applied - 100g provides 1N of force.
Repeat 10cm in from the end of the ruler, Keep recording mass and moving in towards pivot by 10cm until 20cm from pivot.
Try the same experiment but with the pivot 10cm from the load and 20cm from the load.
Masses may fall, ensure working in the centre of the desk so that any masses which do fall from the ruler will not fall further onto the floor and feet. The practical should be carried out stood up so that if any masses do fall experimenters can quickly move out of the way.