11.2 - Forces

Question 1

What is equilibrium?

Answer 1

No result force, so no change or movement

action and reaction forces equal / opposite

Question 2

What is weight?

Answer 2

mass x grav potential energy

m x 9.81 Newtons

Question 3

Moon grav pot energy?

Answer 3

1.622 m/s2

Question 4

What is density?

Answer 4

Mass per unit volume

p (rho) = m / V kg/m3

Question 5

Density of materials?

Answer 5

Concrete - 2400
Ali - 2700 (rel. 2.7)
Brass - 8500 kg/m3

Question 6

Properties of force?

Answer 6

Size (magnitude)
Direction of action
Point of application

Question 7

What is pressure?

Answer 7

Stress, a force applied to an object, eg floor, wall

P = F / A

Question 8

What are moments?

Answer 8

Force that produces a turning effect

M = F x distance (force from turning point) Nm

Question 9

What are the units of temp?

Answer 9

C, F and K

Question 10

Celsius to Fahrenheit?

Answer 10

F = (C x 9/5) + 32

Question 11

Celsius to Kelvin?

Answer 11

K = C +273

Question 12

What is thermal expansion?

Answer 12

When heated, gases, liquids and solids will expand

change in length = coeff (alpha) x length x (temp rise)

Question 13

Coefficient of linear expansions (alpha)?

Answer 13

iron - 0.000010
Steel - 0.000012
Ali - 0.000024

Question 14

Modes of heat transfer?

Answer 14

Conduction (touch)
Convection (radiator)
Radiation (empty space, we absorb rad via the sun)

Question 15

What is specific heat capacity?

Answer 15

The heat required to raise the temperature of the unit mass of a given substance by a given amount (usually one degree)

Question 16

Thermal energy equation?

Answer 16

Q = mass x SHC x change in temp Joules

Question 17

SHC of materials?

Answer 17

Copper - 380 J/kg.K
Iron - 450
Steel - 490

Question 18

Coefficient of friction equation?

Answer 18

mu = Friction / Normal force
mu = Friction / mass x grav pot energy

Question 19

Coefficient of friction examples?

Answer 19

Rubber on concrete - static = 1, kinetic = 0.8

Teflon on Teflon - static = 0.04, kinetic = 0.04

Question 20

Types of bonding?

Answer 20

Ionic (electrovalent)
Covalent
Metallic

Question 21

Series resistors?

Answer 21

Total R = R1 + R2 …

Question 22

Parallel resistors?

Answer 22

1/RT = 1/R1 = 1/R2 …

Question 23

Earth’s magnetic poles?

Answer 23

North is actually a magnetic south pole

South is magnetic north

Question 24

Flow of magnetism?

Answer 24

North to South

Question 25

How to store magnets?

Answer 25

In pairs, using soft iron keepers

Question 26

Concentric circles?

Answer 26

magnetic flow around a conductor, strongest at the conductor itself

Question 27

Right hand rule?

Answer 27

Hand is conductor
thumb is current flow
fingers show direction of magnetic flux

Question 28

Current flow symbols?

Answer 28

dot = flow towards you
cross = away from you

Question 29

How to strengthen magnetic field?

Answer 29

Shape a conductor into a loop (concentrated mag flux in centres) or coiled form to create a solenoid (resembles magnet), having a soft iron (ferromagnetic) core

Question 30

What are relays?

Answer 30

Electrochemical devices consisting of a coil of wire wound on a ferromagnetic core fitted with a moving armature
linked to a set of switch contacts that make or break when the device is actuated

Question 31

How does a relay work?

Answer 31

when sufficient current is applied, the resulting mag field will magnetise the core, pulling the arm towards the core, opening or closing the relays electrical contacts