Topic 9 - Motion in fields Flashcards
Are the vertical and the horizontal components of velocity for a projectile in a uniform field independent?
Yes
Describe the trajectory of projectile motion in the absence of air resistance
It’s parabolic.
Sketch the trajectory of projectile motion in the absence of air resistance
Describe the effect of air resistance on the trajectory of a projectile
- Air resistance provides a force which opposes motion
- Acceleration will be reduced for falling objects and increased for objects moving upwards
- The trajectory will no longer be parabolic or symmetric
Define the instantaneous velocity of a projectile
Define gravitational potential at a point
The work done per unit mass in bringing a small test mass from infinity to that position
Define gravitational potential energy of a system
The work done when bringing all the masses of the system to their present positions, assuming that they were originally at infinity.
Gravitational potential energy stored between to masses m1 and m2, separated by a distance r:
When is gravitational potential energy equal to zero?
When an object is at infinity.
Define gravitational potential due to a point mass
Define the gravitational potential difference between two points as the work done when moving a unit mass between those points
How do you get the potential due to one or more point masses?
By adding up the potentials
Is gravitational potential a vector or a scalar quantity?
Scalar.
Sketch and describe the pattern of equipotential surfaces due to one point mass
- Circular lines around the point mass
- The lines get further apart as the distance increases
Sketch and describe the pattern of equipotential surfaces due to two point masses
- Just like contour lines
What is the relationship between equipotential surfaces and gravitational field lines?
Field lines are always perpendicular to equipotential lines, pointing from a higher potential to lower potential.
Define escape speed, vesc
A theoretical speed that a projectile of mass m2 needs to escape from a planet’s (m1) force of attraction
Define electric potential (at a point)
The work done per unit charge in bringing a small positive test charge from infinity to that position:
Define electric potential energy
The work done when bringing all the charges of the system to their present positions, assuming that they were originally at infinity.
Define the electric potential due to a point charge
How is the overall electric potential at a point determined?
By adding up individual potentials.
What is the relationship between equipotential surfaces and electric field lines?
Field lines are always perpendicular to equipotential lines and point from higher to lower potential
Sketch the pattern of equipotential surfaces due to one point charge
Sketch the pattern of equipotential surfaces due to two equal point charges
Sketch the pattern of equipotential surfaces due to two opposite point charges
What is a dipole?
A pair of equal and opposite charges separated by a small distance
What provides the centripetal force for circular orbital motion?
Gravitation
State and derive Kepler’s third law
For all the planets orbiting the sun, the average radius cubed is proportional to the period squared
Derive and state the expressions for kinetic energy, potential energy, and total energy of an orbiting satellite
Sketch a graph showing the variation with orbital radius of the kinetic, gravitational potential, and total energy of a satellite
When is weightlessness possible?
- When a body is in deep space where there is no significant graviational field
- When a body is at a point where the gravitational forces of two or more fields cancel each other out
- During free fall
