Practical 2 - Determination of unknown masses using the principal of moments

Question 1

What are the apparatus for this practical?

Answer 1

-Nail to pivot ruler at the 70cm mark
-Metre long ruler
-Clamp and stand
-200g mass and hanger
-Loops of thread

Question 2

At what point do we nail the ruler to create its pivot?

Answer 2

70cm mark

Question 3

What does a risk assessment apply to?

Answer 3

People AND equipment

Question 4

What are three hazards of this practical?

Answer 4

-Pointy nail
-Stand + clamp
-Loose weight

Question 5

What’s the risk with a pointy nail?

Answer 5

Eye injury

Question 6

What’s the control measure for a pointy nail?

Answer 6

Clamp the pointy end facing away

Question 7

What’s the risk with the stand and clamp?

Answer 7

Toppling/mass falling over -injury or damage equipment

Question 8

What’s the control measure for the stand and clamp?

Answer 8

Use a G-clamp

Question 9

What’s the risk with the loose weight?

Answer 9

Sliding off ruler

Question 10

What’s the control measure for the loose weight sliding off the ruler?

Answer 10

Use both hands

Question 11

What’s the first stage in completing this practical?

Answer 11

-Loop the 200g (1.96N) over the metre rule uni it’s horizontal + note down the distance (l) from the point
-Can now calculate the mass (or weight) of the metre rule using the principal of moments

Question 12

Which principle do we use to do our calculations in this practical?

Answer 12

The principle of moments

Question 13

How do we know that 200g = 1.96N?

Answer 13

W = mg
W = 0.2 x 9.81
W = 1.96N

Question 14

What’s the equation used to calculate the weight of the metre rule?

Answer 14

0.20 x metre rule weight = l x 1.96

Question 15

Why do we use 0.20 in these calculations?

Answer 15

It’s the distance from the weight force (in the centre - 0.5m) to the pivot (0.7m)

Question 16

What’s the second stage of completing this practical?

Answer 16

-Replace the 200g mass with an unknown weight (W) and adjust the position until it balances again
-Measure the distance, d, of the unknown weight from the pivot - can now calculate the unknown weight again using the principle of moments

Question 17

What’s the equation used to calculate the unknown weight?

Answer 17

0.2 x metre rule weight = d x unknown weight

Question 18

How do we convert the unknown weight into a mass?

Answer 18

Divide it by 9.81

Question 19

With what do we check the real weight at the end?

Answer 19

Top pan balance

Question 20

What’s the uncertainty of our measurements on a 1m ruler with mm measurements?

Answer 20

+-0.001m

Question 21

How do we calculate the % uncertainty of our answer?

Answer 21

% u = add the uncertainties
——————————— x final answer of the mass
100

Question 22

What’s the relationship between the unknown mass and the uncertainty?

Answer 22

Lighter unknown mass = Higher uncertainty

Question 23

Name two factors that could lead to additional uncertainty in the measurements

Answer 23

-uncertainty of the 200g mass
-beam may not have been exactly level - could use a spirit or a laser level to improve this

Question 24

What could we use the ensure that the beam is definitely level?

Answer 24

A spirit or even a laser level

Question 25

How do we get the absolute uncertainty over a spread of data?

Answer 25

Range
———
2