Mechanics and Materials

Question 1

Breaking stress

Answer 1

The maximum stress that an object can withstand before failure occurs.

Question 2

Brittle

Answer 2

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

Question 3

Centre of mass

Answer 3

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

Question 4

Conservation of energy

Answer 4

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

Question 5

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

Couple

Answer 6

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

Question 7

Density

Answer 7

The mass per unit volume of a material.

Question 8

Efficiency

Answer 8

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

Question 9

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

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

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

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

Equilibrium

Answer 13

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

Question 14

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

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

Inelastic collision

Answer 16

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

Question 17

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

Momentum

Answer 18

The product of an object’s mass and velocity.

Question 19

Newton’s first law

Answer 19

An object will remain in 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

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

Newton’s third law

Answer 21

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

Question 22

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

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

Scalar

Answer 24

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

Question 25

Spring constant

Answer 25

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

Question 26

Stiffness

Answer 26

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

Question 27

Tensile strain

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

Tensile stress

Answer 28

The amount of force acting per unit area. Its unit is the Pascal (Pa).

Question 29

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

Vector

Answer 30

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

Question 31

Young Modulus

Answer 31

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