Work Package 1

Question 1

what is a centroid?

Answer 1

the centre of balance for a 2d shape

Question 2

what is the centre of mass?

Answer 2

the centre of balance for a 3d shape

Question 3

what is the centre of gravity?

Answer 3

virtually the same as the centre of mass but allows for a variable gravitational field

Question 4

What use is the centroid/ centre of mass/ centre of gravity to a designer? (3)

Answer 4

1. ensuring the stability of a product
2. ensuring ease of use of a product
3. ensuring optimal loading

Question 5

how are centroids determined? (3)

Answer 5

1. measurement - find the centre of balance
2. mathematical calculations - divide the object into small areas and work out the sum of their centroids/ centre of gravities
3. computer-aided analysis - using the mass properties tool in a cad system

Question 6

what are newtons three laws?

Answer 6

1. every object in a state of uniform motion tends to remain in that state of motion unless an external force is applied to it.
2. the relationship between an objects mass (m), its acceleration (a) and the applied force (f) is f=ma
3. for every action there is an equal and opposite reaction

Question 7

give two more facts about newtons first law ‘every object in a state of uniform motion tends to remain in that state of motion unless an external force is applied to it’:

Answer 7

1. can refer to objects that are moving at a constant velocity or that are stationary
2. also applies with forces acting together on an object and they cancel each other out

Question 8

whats the calculation of force and what is force measured in? (given)

Answer 8

f = mass (kg) x acceleration (ms−2)

force is measured in kgms-2

Question 9

what is the value to use for gravity?

Answer 9

9.81 ms-2

Question 10

whats the formula for gravitational force?

Answer 10

f = mass x g

Question 11

what is the formula for static friction/ friction force? (given)

Answer 11

f = μ x normal reaction

Question 12

what is this symbol μ?

Answer 12

coefficient of friction

Question 13

what is the calculation for mechanical advantage? (given)

Answer 13

load /effort (force produced divided by force exerted)

Question 14

what is the calculation for velocity ratio? (given)

Answer 14

distance moved by the effort or distance moved by load (a.k.a. leverage ratio)

Question 15

what is the calculation for efficiency (%)? (given)

Answer 15

(mechanical advantage /velocity ratio) x100

Question 16

how do we determine forces? (3)

Answer 16

1. measurement (spring balances, sensors)
2. mathematical measurements (i.e. calculate the theoretical load passing through a product)
3. computer-aided analysis

Question 17

why do designers need to think about forces? (3)

Answer 17

1. ensuring the ease of use of a product (e.g. making sure its not too difficult to turn a handle on a can opener)
2. making sure that the load on a product doesn’t exceed its strength
3. minimising the amount of effort lost through friction