Physics Unit 4 Revision Notes

Some revision notes that I made for unit 4 of physics. Covers basically everything on the specification

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Physics Unit 4 Revision Notes
Further Mechanics
Momentum
Momentum is a measure of how hard it is to stop something
= mv
In any collision total momentum is constant provided no external forces act.
There are two types of collision; elastic and inelastic. In an elastic collision kinetic energy is conserved.
In an inelastic collision kinetic energy is not conserved.
Force is the rate of change of momentum.
(mv)
F = t
The change in momentum is demonstrated as the area under a force-time graph.
Circular Motion
Linear velocity is the speed an object moves in a straight line and is given by:
v = 2rf or v = 2r
t
Angular speed is the angle an object rotates through per second and is given by:
= 2f or = 2
t
By combining the above equations we can see that linear speed and angular speed are linked by the
equation v = r
For an object to move at a constant speed in a circular path there needs to be a centripetal force (The
force which acts towards the centre of the circle). The centripetal force is given by the equation:
F = mv2
r
The body is also undergoing constant acceleration because velocity changes with direction and the
body is constantly changing direction. Centripetal acceleration is given by the equations
a= v2
r or a = 2r
Simple Harmonic Motion
Simple harmonic motion is where an object oscillates to and fro on either side of a mid-point. Some
examples of oscillators include a simple pendulum, a child on a swing, a bungee jumper and a
vibrating springboard.

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Key terms:
Amplitude, A, is the maximum displacement from the equilibrium position.
Period, T, is the time for one complete cycle of oscillations
Frequency, f, is the number of complete oscillations per second
There are two criteria for simple harmonic motion:
1. The acceleration of the body is proportional to its displacement from the equilibrium position
2.…read more

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This shows that the kinetic energy of the system is at a maximum at the equilibrium position and the
potential energy of the system is at a maximum at the maximum amplitude.
In a simple pendulum the time period of each oscillation is affected only by the length of the string
and the gravitational field strength (usually 9.81Nkg-1). It does not vary with amplitude.…read more

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Gravitation
Newton's Law
Newton's law of gravitation states that the attractive force between two point masses is
proportional to the product of the two masses and inversely proportional to the square of the
distance between them.
This is also written as:
F = (-) GMm
r2
Gravitational Field Strength
A field is a volume of space where a suitable test object experiences a force. Field strength is the
force experienced by a unit test object. The test object for gravitation is a 1kg mass.…read more

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The value of g is inversely proportional to r2 in a radial field. The value of g in a radial field is given by
g= GM
r2
Gravitational potential
Gravitational potential is the work done in bringing a unit mass from infinity to that point.
Gravitational potential is zero at infinity.…read more

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Orbits of planets and satellites
See circular motion for more information
Planets and satellites are kept in orbit by the gravitational pull of the earth. This acts as a centripetal
force. As planets and satellites have nearly circular orbits the equations of circular motion can be
used.
In a circular orbit a satellites speed and distance are constant so potential energy and kinetic energy
are both constant.…read more

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The magnitude of E in a radial field is given by
Q
E= 4r2
A uniform field can be created by connecting opposite poles of a battery to two parallel plates.
The direction of the field is always from the positive plate to the negative plate. As the field is
uniform the field lines are equal distances apart. The dotted lines are equipotentials, or lines of equal
electric potential.…read more

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Motion of charged particles in electric fields
The force on a charged particle in a uniform electric field is F=QE. The direction of the force is also
constant. The particle will travel in a parabolic path. After the particle has left the electric field it will
travel in a straight line as it is no longer acted upon by a force.…read more

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Energy stored by a capacitor
Energy stored by a capacitor is given by the area under the graph of potential difference against
time.…read more

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A capacitor discharges exponentially. The equation for the discharge of a capacitor is
-t
Q = QoeRC
The same equation is true for current and voltage
Time constant
The time constant, , is the time it takes for the charge to fall to 1 (roughly 37%) of its original value.
e
The time constant varies with the resistance of the circuit and with the capacitance.…read more

Comments

The Showstopper :)


Thank u so much for ur help :)

Ur notes are really useful and well structured...

Keep up the good work :)

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