4. Mechanics And Materials Definitions

Question 1

Define breaking stress

Answer 1

The maximum stress that an object can withstand before failure occurs

Question 2

Define brittle

Answer 2

A brittle object will show very little strain before reaching its breaking point

Question 3

Define centre of mass

Answer 3

The single point though which all the mass of an object can be said to act

Question 4

Define conservation of energy

Answer 4

Energy cannot be created or destroyed- it can only be transferred into different forms

Question 5

Define conservation of momentum

Answer 5

The total momentum of a system before an event must be equal to the total momentum of the system after the event, assuming no external forces act.

Question 6

Define couple

Answer 6

Two equal and opposite parallel force that act on object through different lines of action. It has the effect of causing a rotation without translation.

Question 7

Define density

Answer 7

The mass per unit volume of a material

Question 8

Define efficiency

Answer 8

The ratio of useful output to total input for a given system

Question 9

Define elastic behaviour

Answer 9

If a material deforms with elastic behaviour, it will return to its original shape when the deforming forces are removed. The object will not be permanently deformed.

Question 10

Define elastic collision

Answer 10

A collision in which the total kinetic energy of the system before the collision is equal to the total kinetic energy of the system after the collision

Question 11

Define elastic limit

Answer 11

The force beyond which an object will no longer deform elastically and instead deform plastically. Beyond the elastic limit, when the deforming forces are removed, 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. It is equal to the work done to stretch the object and can be determined from the area under a force-extension graph.

Question 13

Define equilibrium

Answer 13

For an object to be in equilibrium, both the resulting force and resultant moment acting on the object must be equal to zero.

Question 14

Define Hooke’s Law

Answer 14

The extension of an elastic object will be directly proportional to the force applied to it up to the object’s limit of proportionality

Question 15

Define impulse

Answer 15

The change of momentum of an object when a force acts on it. It is equal to the product of the force acting on the object and the length of time over which it acts

Question 16

Define inelastic collision

Answer 16

A collision in which the total kinetic energy is the system before the collision is not equal to the kinetic energy of the system after the collision

Question 17

Define moment

Answer 17

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

Question 18

Define momentum

Answer 18

The product of an object’s mass and velocity

Question 19

Define Newton’s first law

Answer 19

An object will remain it its current state of motion, unless acted on by a resultant force. An object requires a resultant force to be able to accelerate

Question 20

Define Newton’s second law

Answer 20

The sum of the forces acting on an object is equal to the rate of change of momentum of the object

Question 21

Define Newton’s third law

Answer 21

Every action has an equal and opposite reaction. If an object exerts a force on another object, the the other object must extend a force back, that is opposite in direction and equal in magnitude.

Question 22

Define plastic behaviour

Answer 22

If a material deforms with plastic behaviour, it will not return to its original shape when the deforming forces are removed. The object will be permanently deformed.

Question 23

Define the principle of moments

Answer 23

For an object to be in equilibrium, the sum of the clockwise moments acting about a point must be equal to the sum of the anticlockwise moments acting about the point.

Question 24

Define scalar

Answer 24

A scalar quantity is one that only has a magnitude. Examples include length, mass and temperature.

Question 25

Define spring constant

Answer 25

The constant of proportionality for the extension of a spring under a force. The higher the spring constant, the greater the force needed to achieve a given extension.

Question 26

Define stiffness

Answer 26

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

Question 27

Define tensile strength

Answer 27

The ratio of an object’s extension to its original length. It is a ratio of two lengths and so has no unit.

Question 28

Define tensile stress

Answer 28

The amount of force acting per unit area. Its unit it the pascal (Pa)

Question 29

Define terminal speed

Answer 29

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

Question 30

Define vector

Answer 30

A vector quantity is one that has both a magnitude and a direction. Examples include velocity, displacement and acceleration.

Question 31

Define Young modulus

Answer 31

The ratio of stress to strain for a given material. Its unit is the Pascal (Pa).