# edexcel unit 4 physics revision material

some edexcel specification revision notes

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## Linear Momentum

p = mv

UNITS: kgms-1

momentum is a vector (because velocity is a vector)

Δp α F(resultant)                                 Δp                               Impulse = Δp

F   t

The impulse of a force is equal to the change in momentum of a body which a force causes.

Impulse = F x Δt

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## Conservation

Conservation of Momentum

Momentum is ALWAYS conserved.

Conservation of Energy

Energy cannot be created or destroyed, it can only be transferred from one form to another.

There are 2 types of collision

Elastic                            Inelastic

- KE is conserved           - KE is NOT conserved

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## Circular Motion

Angular velocity - the angular speed of an object in a particular direction

ω = θ/t                       v = rω

ω = 2π/T

where; ω = angular velocity (rad s-1)

t = time T = period r = radius

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## Centripetal Force

F = mv2/r

where m = mass v = velocity r= radius

other formula to be aware of:

a = rω2                            where a = acceleration

substitute in to centripetal force equation;

F = mrω2                                           where F = force

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## Electric/Magnetic Fields

If a charged object is placed in an electric field it will experience a force.

Coloumbs Law

This states that the force of attraction or repulsion between two point charges is equal to k (constant in formula book) multiplied by (charge 1 x charge 2) divided by the radius2. A point charge has a radial field. Uniform field is produced by two parallel plates. From POSITIVE to NEGATIVE.

Electric Field Strength (E): the force that a charged particle will feel i.e. how tightly packed the field lines are.

Charge (Q): Charge on a particle in coloumbs.

F = EQ                     E = F/Q       UNITS: NC-1

Using F = ma, we can say F= F and that a = EQ/m

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## Uniform Fields

UNIFORM Electric field strength (E): a measure of how rapidly the potential changes.

Given by;

E = V/d                 UNITS: Vm-1

where V = potential difference      d = distance over the potential difference

The distance will be the same throughout a uniform field as the lines are parallel to each other. Therefore, in a uniform field, the firld strength will be the SAME AT ALL POINTS.

*Permittivity of free space: measure of how easy it is for electric field to pass thru space = Є0

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