Principle of moments Done By : Low Zhen Jie

Cheng Ivy Miao Jing Deborah Lye

Our instrument

A B

The unknown mass

Retort stand

Meter rulers

Materials used

• 2 pulleys • 2 metre rules • Retort stand • Weights • String

• Instead of using the DOWNWARD force of gravity which is used in the weight balance, our group makes use of the UPWARD force by using pulleys to reverse the direction of gravity

• Our machine uses not one, but two rulers. And it is innovative as the ruler on the bottom ensures accuracy of results.

Equilibrium of forces• Clockwise moments= Anti-clockwise moments • No net force • No acceleration • At rest • Both sides of the balance are at rest and

therefore have the same force – weight.

How we determine the weight of the object

• Put enough weights at the other side to roughly balance out the sides.

• Also adjust the pulleys with the place the string is tied to the bottom of the ruler.

• The moment on the left side has to be equal to that of the right side.– Meaning, the ruler at the bottom will need to

balance.

Calculation

Left hand side:Mass of A × Perpendicular length

Right hand side:Mass of B × Perpendicular length

Why?

By calculating the moments of a force!Moment= F x L, where F is the magnitude of the

force and L is the perpendicular distance. In this case, L is where the string is tied to the

ruler (and making sure the string is straight), and F is the weight of the object.

• Since in the formula, F cannot be changed as the weight of an object is a constant. The L, perpendicular distance can change the moment of a force.

Range of measurements of our instrument.

• Between 0 – 1000 grams • Precision : +/- 0.5 grams