Gravitational Fields Flashcards
(28 cards)
Describe Newton’s law of gravitation.
The force between two masses is:
- Always attractive,
- Directly proportional to the product of the masses,
- Inversely proportional to the square of the distance between them.
Define gravitational field strength in words.
Force per unit mass on an object due to a gravitational field.
Give two units for gravitational field strength.
- N kg-1
- m s-2
Is gravitational field strength scalar or vector? What significance does this
have when combining field strengths?
- Vector quantity.
- Direction must be considered when combining.
What do gravitational field lines show?
- The direction of the force,
- that a mass would feel in a gravitational field.
Sketch a radial gravitational field and describe the key features.
- Field lines meet in the centre.
- Field strength decreases with distance.
- Shown by field lines getting further apart.
Sketch a uniform gravitational field and describe the key features.
- Field strength is constant.
- Shown by equally spaced parallel lines.
- The surface of a planet can be approximated as a uniform field.
Define gravitational potential at a point in a gravitational field.
- Work done per unit mass
- To move an object from infinity to that point.
Why is gravitational potential negative?
- Gravitational potential is defined as zero at infinity.
- And work needs to be done on an object to move it to infinity.
What are gravitational equipotentials?
- Lines or surfaces connecting points of equal gravitational potential.
- (Usually shown at equal intervals of gravitational potential.)
How much work is done moving an object along an equipotential?
Zero as there is no change in gravitational potential.
What do you know about the
direction of equipotentials relative to field lines?
Equipotentials and field lines are always perpendicular.
Explain the spacing of the equipotentials in a radial field.
- Get further apart as distance from mass increases.
- For a given energy per unit mass, an object can be moved further, as field strength decreases.
Explain the spacing of the equipotentials in a uniform field.
- Equally spaced as distance from mass increases.
- For a given energy per unit mass, an object can be moved an equal distance, as field strength is constant.
gravitational field strength
can also be referred to as…
Gravitational potential gradient.
What does the magnitude of the gradient of a graph of gravitational potential V against distance r
represent?
Gravitational field strength (g)
If equipotentials are closer together, what does this tell you?
- Greater rate of change of gravitational potential V with distance r (i.e. greater ΔV/ Δr).
- Which means a greater gravitational field strength g.
What does the area under a graph of gravitational field strength g against
distance r represent?
Gravitational potential difference ΔV.
Is gravitational potential scalar or vector? What significance does this
have when combining potential?
- Scalar quantity.
- Direction does not need to be considered.
At a point between the Earth and Moon, the overall gravitational potential is at a maximum. What do you know about the gravitational field strength at this point?
- It is zero.
- The gradient = - g and at a turning point this is zero.
What provides the centripetal force for a satellite orbiting a larger mass?
The gravitational force (given be Newton’s law of gravitation).
If the radius r of a satellite’s orbit
increases, what happens to its linear speed v and orbital period T?
- Linear speed decreases.
- Time period increases.
What do you know about the total energy of a satellite?
- Total energy = kinetic energy + gravitational potential energy
- Total energy is constant at all points in the orbit.
Define escape velocity.
- The minimum speed an unpowered object needs,
- In order to leave the gravitational field,
- And not fall back due to gravitational attraction.
