9.2+Gravitational+field,+potential+and+energy

BACK TO IB PHYSICS > MOTION IN FIELDS
 * 1 Measure || 2 Mech || 3 Therm || 4 Waves || 5 Electric || 6 Fields 7 Atomic || 8 EPCC || 9 Motion in Fields || 10 Therm AHL || 11 Wave Phen || 12 EMI || 13 QNP || 14 Digital || OPT || PRAC || REVISE ||

=GRAVITATIONAL FIELD, POTENTIAL AND ENERGY= 9.2.1 Define gravitational potential and gravitational potential energy. Students should understand the scalar nature of gravitational potential and that the potential at infinity is taken as zero. Students should understand that the work done in moving a mass between two points in a gravitational field is independent of the path taken. 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; all GPE is a negative quantity since the force is always attractive.

GRAVITATIONAL POTENTIAL: The energy needed per kilogram to bring a test mass from infinity to a point in a gravitational field. Measured in Jkg-1.

The test mass is brought from infinity (where its potential is zero). Since the gravitational force is attractive, the work required is negative.

CONSERVATIVE FIELD: The energy needed to bring a mass to a point is the same whichever path the mass follows. This follows from the principle of conservation of energy. A gravitational field is conservative.

9.2.2 State and apply the expression for gravitational potential due to a point mass. QUESTION: What is the potential at the surface of the Earth? (The Earth is not a point mass but we can treat it as such).

9.2.3 State and apply the formula relating gravitational field strength to gravitational potential gradient. POTENTIAL GRADIENT: The change in potential per metre. Gravitational field strength is the negative of potential gradient.

9.2.4 Determine the potential due to one or more point masses.

EQUIPOTENTIAL: Lines or surfaces which join points at the same potential. They are always perpendicular to the gravitational field lines. 9.2.5 Describe and sketch the pattern of equipotential surfaces due to one and two point masses.

9.2.6 State the relation between equipotential surfaces and gravitational field lines. 9.2.7 Explain the concept of escape speed from a planet.

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

9.2.8 Derive an expression for the escape speed of an object from the surface of a planet. Students should appreciate the simplifying assumptions in this derivation. 9.2.9 Solve problems involving gravitational potential energy and gravitational potential.