Principle of moments
Done By : Low Zhen Jie
Cheng Ivy
Miao Jing
Deborah Lye
Our instrument
Meter rulers
The unknown mass
A
B
Retort stand
Materials used
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2 pulleys
2 metre rules
Retort stand
Weights
String
Why is our invention innovative
and creative?
• 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
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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