Topic 4: 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.
alternatively:
The point of an object where if a force is applied no turning effect is produced.

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

Question 14

tensile stress

Answer 14

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

Question 15

terminal speed

Answer 15

The maximum speed at aqual to each ours when the resistive and driving forces acting on the object are equal to each other.

Question 16

vector

Answer 16

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

Question 17

Young’s modulus

Answer 17

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