# PH1.1

Ph1

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## Vectors and Scalars

VECTORS contain magnitude and direction.

i.e momentum, acceleration, velocity, weight, force

SCALARS contain magnitude only.

i.e. time, density, speed, distance, energy. pressure

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## Newtons 3rd law

"If object A exerts a force on object B, then object B exerts an equal but opposite force on object A."

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## Turning Effects

A moment is a turning effect of a force.

It can also be called a torque.

Moment = force X perpendicular distance from pivot

(Nm)       (N)                           (m)

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## Principle of Moment

For a body to be in equilibrium:

• Sum of the clockwise  = Sum of anticlockwise             moments                 moments
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## Conditions for equilibrium

For an object to be in equilibrium:

• NO NET FORCE ACTING IN ANY DIRECTION
• NO NET TURNING EFFECT ABOUT ANY POINT
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## Centre of Gravity & Centre of Mass

Centre of Gravity of an object is the point at which we can take its entire weight to act.

Centre of Mass of an object is the point at which we can takes its entire mass to act.

When an object is outside the base it will topple.

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## Displacement

The displacement of point B from point A is the shortest distance from A to B, together with the distance.

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## Speed Definitions

Mean Speed: total distance travelled / total time taken

Instantaneous Speed: rate of change of distance

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## Velocity Definitions

Mean velocity: total distance/ total time taken

Instantaneous Velocity = rate of change of displacement

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## Acceleration definitions

Mean Acceleration = change in velocity / time      taken

Instantaneous Acceleration =  rate of change of velocity

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## Terminal Velocity

Terminal velocity occurs when the frictional force = driving force.

The driving force must be constant and the frictional force must increase with speed.

Graphs of terminal velocity

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## Work

Work done = Force x Distance moved in direction of force

Work Done units are JOULES however its base units are Nm.

Area under a Force-distance graph = Work done

Work Done = Energy transferred

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## Hookes Law

"Tension in the spring/wire is proportional to its extension from its natural length, provided the extension is not to great."

Stretching force (F) =spring constant (K)  X extension (x)

The spring constant is sometimes called the stiffness.

Force extension graph.

Elastic potential energy = 0.5 X Stretching force X extension  (AREA UNDER GRAPH)

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## Interchange between KE & PE

PE LOST = KE GAINED

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## Conservation of energy

"Energy cannot be created or destroyed only transferred from one for the another."

Gravitational potential energy = mgh

Kinetic energy =

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## Power

Power is the rate of energy transfer.

Power = work done / time.

Power is measured in WATTS.

1 Watt = 1 joule per second

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## Static electricity

Static electricity is caused by the transfer of electrons for one object to another.

Neutral atoms can lose or gain electrons these atoms become positively or negatively charged.

These charged atoms are called ions.

GAIN ELECTRONS = - VE

LOSE ELECTRONS = +VE

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## Electric Current

Current = Rate of flow of charge

Charge = current X time

Charge is measured in Coulombs.

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## Derive I = nAve

Volume = Al

Number of free electrons per m = nAl

Charge = nAle

As current = charge/ time

I= nale/t

As v = l/t

Therefore I= nAve

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## Conduction in Metals

Free electrons collide with lattice ions.

Kinetic energy is transferred from the electrons to the ions therefore energy is transferred.

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## What factors effect current?

(I = nAve )

• number of charge carriers per m
• cross sectional area of conductor
• The drift speed of the charge carrier
• Charge on an electron

What type of charge carriers carry electricity in a gas?

• Electrons and positive ions
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## Define A Volt

"The potential difference between 2 point in a circuit when 1 joule of work in transferring 1 coulomb of charge from 1 point to the other. "

Units: V = Jc

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## Current-Voltage Graph

• Semi-conductor Diode
• filament lamp
• metal wire at constant temperature
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## Ohm's Law

"Voltage is proportional Current provided temperature is constant."

Ohms law graph

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## Resistance

"Resistance of a conductor is the ratio of p.d applied across it, to the current passing through."

Resistance is measured in ohms (       ).

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## Superconductors

A superconductor is a material with zero resistance.

As there are no collisions in a superconductor there is no energy transferred therefore no heat lost

For a material to become a superconductor must be cooled below its transition temperature.

To cool material use liquid nitrogen

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## IN SERIES

IN SERIES:

• Current is the same at all points
• Voltage splits
• R = R + R
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## In Parallel

IN PARALLEL:

• current splits up
• Voltage stays the same.
•
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## EMF

Emf = electromotive force

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## V = E -ir

V = energy delivered per unit charge to external                circuit

E= energy supplied per unit charge to circuit from           chemical energy of cell.

Ir= Energy lost in internal resistance

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