Chapter 7~ Matter And Materials

Question 1

What is the definition of density?

Answer 1

°Mass per unit volume of a substance

>property of matter
>is constant
>measure of how concentrated the matter is in a particular material
>symbol 'p' - rho
>unit kgm-3 or gcm-3

Question 2

Formula for density

Answer 2

p=m/v

Density =mass /volume

Question 3

1000kgm-3=

Answer 3

1gcm-3

Question 4

Density of water 💦?

Answer 4

1000kgm-3

Question 5

Pressure is defined as….. ?

Answer 5

°As the normal force acting per unit cross- sectional area

> a fluid exerts pressure on walls of its container, or on any surface with which it is in contact
unit : Pa

Question 6

What produces a high pressure?

Answer 6

A big force on a small area

Question 7

Formula for pressure

Answer 7

P=F/A

Pressure =force /area

Question 8

1 Nm-2=

Answer 8

1 Pa

Question 9

What is a fluid?

Answer 9

Liquid or gas

Question 10

proportional means….

Answer 10

° 2 variables that also have a constant ratio between them

If one increases the other will as well…. Also if one decreases so does the other

Question 11

Atmospheric pressure is due to..?

Answer 11

Is the weight of the atmosphere above us, pressing downwards. Pulled by gravity

Question 12

Pressure in a liquid depends on 3 things

Answer 12

1. Depth (h) below surface
2. Density (p) of FLUID
3. The acceleration due to gravity, g

Question 13

Pressure is proportionate to… :

Answer 13

density (p), gravity (g) and depth(h)

Question 14

Formula for pressure

Answer 14

P = pgh

Pressure = density Xacceleration due to acceleration X depth

Question 15

How to derive p=pgh

🏝️ water in a tank

Answer 15

1. Volume of water = Area X height

V= A X h

2. Mass of water (m = p X V) = p X A X h
3. Weight if water (Mg) = p X A X h X g
4. Pressure = force ÷ area

P= p X A X H x g/A

5. P = pgh

Question 16

The 2 forces concerned with changing the shape of a spring…

Answer 16

1. Tensile

2. compressive

Question 17

Compressive meaning?

Answer 17

Describes a force that squeezes an object

Question 18

Definition of tensile?

Answer 18

Associated with tension or a pulling force

Question 19

Definition of extension

Answer 19

The change in length of a material from its original length

Question 20

Hooke’s law :

Answer 20

A material obeys Hooke’s law if the extension produced in it is proportional to the applied force (load)

Question 21

Definition of force constant

Answer 21

The ratio of force to extention for a spring/wire.

Unit : Nm-1

Question 22

Elastic limit definition

Answer 22

The value of stress beyond which an object will not return to its original dimensions.

And from that point on plastic deformation takes place

Question 23

Hooke’s law states that

Answer 23

The force applied is proportional to the extention of a material provided Hooke’s limit is not exceeded

Question 24

F=

2 equations

Answer 24

1. ma

2. kx

Question 25

Force constant of spring (k) ‘s unit:

Answer 25

Nm-1

Question 26

Definition of elastic limit

Answer 26

The force beyond which the spring becomes permanently deformed.

Question 27

Definition of strain:

Answer 27

It is defined as the extention per unit length produced by tensile or compressive forces

Question 28

Formula for strain

Answer 28

Strain =extension (x) /original length (l)

Question 29

Stress is defined as…

Answer 29

The force acting per unit cross-sectional area

Question 30

Formula for stress..

Answer 30

Stress =force (F) /cross sectional area (A)

Question 31

Formula for stress..

Answer 31

Stress =force (F) /cross sectional area (A)

Question 32

The 2 units of stress are :

Answer 32

1. Nm-2
2. Pa

Nm-2 = Pa

Question 33

Young modulus is defined as

Answer 33

°the ratio of stress to strain for a given material, resulting from tensile forces, provided Hooke’s law is obeyed

Question 34

Units for young modulus

Answer 34

Pa

Question 35

Formula for young modulus

Answer 35

=stress /strain

Remember : stress =F/A

                   Strain = x/l

Question 36

Young modulus also indicates

Answer 36

The degree of stiffness of a material. The more young modulus, the stiffer it is

Question 37

Stress (y axis) - strain (x axis) graph

Characteristic :

Answer 37

1. Gradient is = to young modulus

Can on use values before or by the elastic limit to get answers…. No values after the elastic limit may be used

Question 38

Definition of elastic potential energy or strain energy :

Answer 38

°energy stored in a stretched or compressed material

> the material warms up slightly once stretched or compressed
= work done

Question 39

Force - extention graph characteristics

Answer 39

1. Gradient is = k

2. Area under the graph is = work done

Question 40

Work done =

Answer 40

1. Force x distance
2. The area under a F-X graph, therefore

      W or E =1/2 k x~2 0.5 times k times x squared

Question 41

Elastic energy on a F-X graph =

Answer 41

E=1/2 F X

Or

E= 1/2. K. X~2
0.5 TIMES K TIME X SQUARED

Question 42

Young modulus =

Answer 42

E= STRESS/STRAIN

OR
E= FL/AX

UNIT : Pa

Question 43

Stress - strain graph

The gradient is =

Answer 43

Young modulus

Question 44

3 types of F-X graphs to represent materials are :

Answer 44

Look at notes to get structure of graphs

1. Polymaterial material graph e.g. Rubber, plastic ( hysterisis loop, due to loading and unloading)
2. Brittle material e.g. Glass
   (constant gradient… Therefore constant k)

3.ductile materials e.g. Wire (constant gradient until Hooke’s limit of proportionality)

Question 45

Work done from a F- X graph

Answer 45

E= 1/2KX~2 - 1/2KX~2

UNIT: J

Question 46

3 ways to work out the work done by a spring

Answer 46

1. W=(1/2) k x^2
2. W= (1/2)Fx
3. Area under a F - x graph

Question 47

What is elastic potential energy?

Answer 47

It is the energy stored in a material that is being deformed.

Or

It is the energy stored in a material due to its tension or compression.