# IB MOTION IN FIELDS DEFINITIONS AND CONCEPTS by stariya

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IB MOTION IN FIELDS DEFINITIONS AND CONCEPTS
COMPONENTS OF PROJECTILE MOTION: The horizontal component has
constant velocity. The vertical component has a constant acceleration. They are
independent and together create a parabolic trajectory.

AIR RESISTANCE: A force which opposes motion and is proportional to the
velocity. This leads to terminal velocity.

GRAVITATIONAL POTENTIAL ENERGY: The energy a body has because of its
position in a gravitational field. Zero GPE is defined as the energy an infinite
distance away; GPE is a negative quantity.

CONSERVATIVE FIELD: The energy needed to bring an object to a point in a field
is the same whichever path the object follows. This follows from the principle of
conservation of energy. Gravitational and electric fields are conservative.

GRAVITATIONAL POTENTIAL: The energy needed per kilogram to bring a test
mass from infinity to a point in a gravitational field. Since zero potential is
defined at an infinite distance, all gravitational potential is a negative quantity.
Measured in Jkg-1.

DEFINING EQUATION OF GRAVITATIONAL POTENTIAL: m is a test mass.

EQUATION FOR GRAVITATIONAL POTENTIAL DUE TO A MASS, m (eg a planet)

POTENTIAL GRADIENT: The change in potential per metre. Gravitational field
strength is the negative of potential gradient. r and g are in opposite directions,
hence the minus sign. Measured in Vm-1.

EQUATION FOR RELATION BETWEEN g AND GRAVITATIONAL POTENTIAL

EQUIPOTENTIAL: Lines or surfaces which join points at the same potential. They
are always perpendicular to the gravitational field lines.

ESCAPE SPEED: The minimum speed of a small mass to escape from the
gravitational field of a planet to infinity.
DULWICH COLLEGE SHANGHAI

ELECTRIC POTENTIAL ENERGY: The energy a charge has due to its position in an
electric field. This can be positive or negative; potential around a positive charge
is positive since work is done to bring a positive test charge nearer. Unit: joule.

ELECTRIC POTENTIAL: The energy per coulomb needed to bring a positive test
charge from infinity to a point in an electric field. Zero potential is at infinity .
Unit: JC-1 or volt (V).

DEFINING EQUATION OF ELECTRIC POTENTIAL: q is a test charge.

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EQUATION FOR POTENTIAL DUE TO A CHARGE q.

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ELECTRIC POTENTIAL GRADIENT: The change in potential per metre. Electric
field strength is the negative of potential gradient. r and E are in opposite
directions, hence the minus sign. Measured in Vm-1.

ELECTRIC EQUIPOTENTIAL: Lines or surfaces joining points in an electric field
which are at the same potential. They are perpendicular to the electric field lines.

EQUATION FOR RELATION BETWEEN g AND GRAVITATIONAL POTENTIAL

CENTRIPETAL FORCE: Orbital motion requires an accelerating force. This is
provided by the gravitational attraction of the masses.

KEPLER’S THIRD LAW: The square of the time of revolution of a planet about the
Sun is directly proportional to the cube of the mean radius of the planet’s orbit.

WEIGHTLESSNESS IN SPACE: True weightlessness would only occur an infinite
distance from the Sun (and other stars). A body in freefall (eg in orbit)
experiences no reaction force from another object (such as a spacecraft) which is
also falling and so the body feels weightless.

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