Mechanics III (Theory)

Work and energy formula

W =Fs

What does W stand for? (Work formula)

Work/energy

What does F stand for? (Work formula)

Force

What does s stand for? (Work formula)

Distance

Unit of W

Joule (J)

Unit for energy

Joule (J)

Energy (definition)

The ability to do work

Forms of energy (10)

Kinetic. Potential. Internal. Electrical. Light. Heat. Chemical. Nuclear. Sound. Magnetic

Principle of conservation of energy (definition)

Energy cannot be created or destroyed only changed from one form to another

Why are kinetic and potential energy are subsets of these?

All forms of energy are subsets of these

Internal energy (Definition)

The sum of the kinetic and potential energy of the atoms/molecules in a substance

Why is internal energy important?

Useless and all useful forms of energy are slowly being turned into it.

Why is electrical energy important?

Easy to convert into other forms

Potential energy (Definition)

Energy an object has due to its position (height off the ground) or condition (squashed or stretched)

Potential energy formula

Ep = mgh

What does Ep stand for? (Potential energy formula)

Potential energy

What does g stand for? (Potential energy formula)

Acceleration due to gravity

What does h stand for? (Potential energy formula)

Depth

Kinetic energy formula

Ek = ½ mv²

What does Ek stand for? (Kinetic energy formula)

Kinetic energy

What does m stand for? (Kinetic energy formula)

Mass

What does v stand for? (Kinetic energy formula)

Velocity

Renewable energy (definition)

Those that will not run out. E.g. solar. Wind. Biomass. Geothermal. Hydroelectric. Waves. Tidals

Biomass (definition)

Energy gained from fast growing plants e.g. Elephant grass. Willow. Oilseed rape

Non-renewable energy (definition)

Those that will run out. E.g. fossil fuels. Turf. Nuclear

Light bulb converts what energy form into what?

Electrical. Light (+Heat)

Washing machine converts what energy form into what?

Electrical. Kinetic Heat and Light (+Sound)

Loudspeaker converts what energy form into what?

Electrical. Sound Kinetic and Light

Microphone converts what energy form into what?

Sound. Electrical Sound and Kinetic

Leaf converts what energy form into what?

Light. Chemical

Coal fire converts what energy form into what?

Chemical. Light Heat and Sound

Battery converts what energy form into what?

Chemical. Electricity

Battery charger converts what energy form into what?

Electrical. Chemical

Human converts what energy form into what?

Chemical. Kinetic Sound Heat Potential and Electrical

Petrol car converts what energy form into what?

Chemical. Kinetic Heat Light Sound and Potential

Advantages of Non-Renewable energy (3)

More reliable. Can be placed anywhere. Relatively cheap to build

Disadvantages of Non-Renewable sources of energy (2)

Causes global warming. More expensive to run

Advantages of Renewable sources of energy (2)

Doesn’t cause global warming. Cheaper to run

Disdvantages of Renewable sources of energy (3)

Not reliable e.g. wind doesn’t always blow. Cannot be placed everywhere. Expensive to build

Efficient use of energy at home (4)

Insulate attic. Insulate the walls. Double/triple glazed windows. Logging jacket around hot water cylinder.

Formula for power

P = W/t

What does P stand for? (Power formula)

Power

What does W stand for? (Power formula)

Work/energy

What does t stand for? (Power formula)

Time

Unit for power

Watt (W)

% Efficiency formula

P_o/p / P_i/p x 100

What does P_o/p stand for? (% Efficiency formula)

Power output

What does P_i/p stand for? (% Efficiency formula)

Power input

Examples of simple harmonic motion (4)

Atoms in a solid. Pistons in a petrol/diesel engine. Boat on a tide in a harbour. A weight on the end of a spring that’s pulled down.

Example of approximate simple harmonic motion

Pendulum

Why is a pendulum an example of approximate simple harmonic motion?

Because it moves in an arc while other examples of simple harmonic motion move in straight lines

Simple harmonic motion (definition)

An object is said to be in simple harmonic motion if its displacement from a fixed point is directly proportional to its acceleration which is always directed towards that point.

Formula for simple harmonic motion + derivation

a∝-s ∴ a = -(constant)s

Why is s negative in the simple harmonic motion formula?

s and a always point in opposite directions

What is a? (Formula for simple harmonic motion)

Acceleration (points towards fixed points)

What is s? (Formula for simple harmonic motion)

Displacement (measured from fixed point)

Hooke’s Law (definition)

The extension of a stretched spring is directly proportional to the force causing it, provided the elastic limit is not exceeded.

Formula for Hooke’s Law

F = -ks

What does F stand for? (Formula for Hooke’s Law)

(Restoring) Force

What does restoring force equal to?

Force of the weight on the spring

What does K stand for? (Formula for Hooke’s Law)

Spring constant

What does s stand for? (Formula for Hooke’s Law)

Extension

Big springs have a … K while small springs have a … K

Large. Spring

Prove that systems that obey Hooke’s Law execute simple harmonic motion

F = -Ks (Hooke’s Law) F=ma (Newton’s second law)

ma=-ks

a =-(k/m)s or a= -(k/m)s

If k and m are constant a= -(constant)s which is the definition of SHM (QED)

Periodic Time (Simple Harmonic Motion) Definition

The periodic time of a particle executing simple harmonic motion is the time interval between when a particle passes a particular point and when it passes the same point again, going in the same direction

Draw a diagram of one period

…

Formula for periodic time

T = 2π/√constant

Periodic time for general simple harmonic motion formula

T = 2π/√K

Periodic time for spring simple harmonic motion formula

T = 2π/√k/m

Periodic time for a pendulum simple harmonic motion formula

T = 2π/√g/l