4. Mechanics and Material - definitions

Question 1

Breaking stress

Answer 1

The maximum stress an object can withstand before failure occurs

Question 2

Brittle

Answer 2

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

Question 3

Centre of mass

Answer 3

the single point of 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 - only transferred into different forms

Question 5

Conservation of momentum

Answer 5

The total momentum of a system before and event must be equal to the total momentum 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 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 of a system

Question 9

Elastic behaviour

Answer 9

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

Question 10

Elastic colision

Answer 10

An elastic collision is when the total kinetic energy of a 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 is deformed plastically. Beyond the elastic limit, when the deforming forces are removed the object does 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 found from the area under a force-extension graph

Question 13

Equilibrium

Answer 13

For an object to be in equilibrium, the resulting forces an momentum acting upon it must be equal to 0

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 limit of proportionality of the object

Question 15

Impulse

Answer 15

The change in momentum of an object when a force acts on it. It is equal to the product of the force acting on it and the 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 an objects mass and distance

Question 18

Newton’s first law

Answer 18

An object will remain in its current state of motion, unless acted on by an external force. An object requires a resultant force in order to accelerate

Question 19

Newton’s second law

Answer 19

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

Question 20

Newton’s third law

Answer 20

Every action has an equal ad opposite reaction. If an object exerts a force on another object it must exert a force back equal in magnitude but opposite in direction

Question 21

Plastic behaviour

Answer 21

If an object deforms plastically then it does not return to its original size when the deforming forces are removed

Question 22

Principle of moments

Answer 22

: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 23

Spring constant

Answer 23

The constant of proportionality for an extension of a string under force. The greater the spring constant the greater force needed to achieve a certain extension

Question 24

Stiffness

Answer 24

A measure of how difficult it is to stress a given material

Question 25

Tensile strain

Answer 25

The ratio of an objects extension to its original length

Question 26

Tensile stress

Answer 26

The amount f force acting per unit area , its unit is Pascal

Question 27

Terminal speed

Answer 27

The maximum speed an object reaches when the driving forces and resistive forces acting on it are equal