mechanics and materials

Question 1

what is the breaking stress of a material

Answer 1

the max stress that an object can withstand before failure occurs

Question 2

define centre of mass

Answer 2

the single point through which all the mass of an object is said to act

Question 3

define conservation of energy

Answer 3

energy cannot be created or destroyed, only transferred

Question 4

define conservation of momentum

Answer 4

the total momentum before an event must be equal to the total momentum after, assuming no external forces act

Question 5

define couple

Answer 5

two equal, opposite and parallel forces that act on an object through different lines of action.

Question 6

define density

Answer 6

the mass per unit volume of a material

Question 7

define efficiency

Answer 7

useful output over total input

Question 8

define elastic behaviour

Answer 8

if a material deforms with elastic behavious, it will return to its original shape when the deforming forces are removed

Question 9

define elastic collision

Answer 9

a collision in which the total KE before is equal to the total KE after the collision

Question 10

define elastic limit

Answer 10

the force beyond which an object will no longer deform elastically, but plastically

Question 11

what happens beyond the elastic limit

Answer 11

the object will not return to its original shape

Question 12

define elastic strain energy

Answer 12

the energy stored in an object when it is stretched

Question 13

what is elastic strain energy equal to?

Answer 13

work done to stretch the object, the area under a force extension graph

Question 14

define equilibrium

Answer 14

both the resultant force and resultant moment acting on a system is equal to zero

Question 15

what is hooke’s law?

Answer 15

the extension of an elastic object is directly proportional to the force applied up to the limit of proportionality

Question 16

define impulse

Answer 16

the change of momentum of an object

Question 17

what is impulse equal to?

Answer 17

the product of the force acting on the object and the length of time over which it acts

Question 18

define inelastic collision

Answer 18

a collision in which the total KE before is not equal to the total KE after

Question 19

define moment

Answer 19

the product of the force and perpendicular distance from the line of action to the pivot

Question 20

define momentum

Answer 20

mass x velocity

Question 21

define newton’s first law

Answer 21

an object will remain stationary or at a constant velocity unless acted on by a resultant force

Question 22

define newton’s second law

Answer 22

the force acting on an object is directly proportional to its acceleration and inversely proportional to its mass

Question 23

define newton’s third law

Answer 23

every action has an equal and opposite reaction.

Question 24

define plastic behaviour

Answer 24

if a material deforms with plastic behaviour it will be permanently deformed

Question 25

define principle of moments

Answer 25

for an object in equilibrium the sum of the clockwise moments must be equal to the sum of the anticlockwise moments

Question 26

define scalar

Answer 26

a quantity that only has magnitude

Question 27

define spring constant

Answer 27

the constant of proportionality for the extension of a spring under a force

Question 28

define stiffness

Answer 28

a measure of how difficult it is to stretch a given object

Question 29

define tensile strain

Answer 29

the ratio of an object’s extension to its original length

Question 30

define tensile stress

Answer 30

the amont of force per unit area, Pa

Question 31

define terminal velocity

Answer 31

the maximum velocity of an object that occurs when the resistive and driving forces acting on the object are equal to each other

Question 32

define vector

Answer 32

a quantity with both magnitude and direction

Question 33

define young modulus

Answer 33

stress/strain