Physics Unit 4 Revision Notes

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…

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…

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…

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…

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…

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…

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…

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…

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

Because the area of a triangle is ½ *base * height the energy
stored by the capacitor is given by the equation

E=1
2QV


The others equations…

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.…