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 from

Question 4

Conservation of Energy

Answer 4

Energy cannot be created nor 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

Efficiency

Answer 7

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

Question 8

Elastic Behaviour

Answer 8

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 9

Elastic Collision

Answer 9

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 10

Elastic Limit

Answer 10

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 11

Elastic Strain Energy

Answer 11

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 12

Equilibrium

Answer 12

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

Question 13

Hooke’s Law

Answer 13

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 14

Impulse

Answer 14

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 15

Inelastic Collision

Answer 15

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 16

Moment

Answer 16

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

Question 17

Newton’s First Law

Answer 17

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 18

Newton’s Second Law

Answer 18

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

Question 19

Newton’s Third Law

Answer 19

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 20

Plastic Behaviour

Answer 20

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 21

Principle of Moments

Answer 21

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 22

Spring Constant

Answer 22

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 23

Tensile Strain

Answer 23

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

Question 24

Tensile Stress

Answer 24

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

Question 25

Terminal Velocity

Answer 25

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

Question 26

Young Modulus

Answer 26

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