Dynamics and Space Flashcards
State what is meant by the term escape velocity:
The minimum velocity required to allow a mass to escape a gravitational field to infinity, where the mass achieves zero kinetic energy and maximum (zero) potential energy.
A stone is stuck in the rim of a wheel. The angular vel of the wheel increase until the stone flies off. Explain in terms of forces why the stone flies off the rim.
The angular velocity increases so the required centripetal force increases
until the friction is insufficient (to hold the stone in place)
State what is meant by moment of inertia.
A measure of an objects resistance to angular acceleration about an axis.
Explain why systematic uncertainties occur.
Scale reading uncertainties are an indication of how precisely an instrument scale can be read.
State what is meant by gravitational field strength.
The gravitational force exerted per unit mass.
State what is meant by a world line:
Line that represents an object on a spacetime diagram.
What will a distance observer notice about time at the event horizon of a black hole?
Time will appear to be frozen.
Explain what is meant by a calibration uncertainty.
Calibration uncertainty arises when there is a difference between a manufacturer’s claim for the accuracy of an instrument when compared with an approved standard.
State what is meant by apparent brightness.
The brightness of a star as measured on
Earth.
Explain what is meant by a non-inertial frame of reference.
Frames of reference that are accelerating (with respect to an inertial frame).
State what is meant by the phrase gravitational lensing.
A distribution of matter (such as a cluster of galaxies) between a distant light source and an observer that is capable of bending the light from the source as the light travels toward the observer.
Explain why electrons follow a curved path between parallel deflection plates.
The electrons travel with constant) horizontal velocity.
Electrons travel with (constant) vertical acceleration.
A car is travelling around a circular track at a constant speed. Explain why it is accelerating.
The car’s direction/velocity is changing. OR
Unbalanced/centripetal/cen tral force acting on the car.
Explain briefly what happens when the hydrogen in a star’s core is depleted.
Nuclear fusion in the core ceases.
Gravitational forces cause both the core & surrounding H shell to shrink.
In stars like the Sun, the H shell becomes hot enough for H fusion to begin.
-> thermal pressure increases & star expands and then cools forming a giant or supergiant
Explain what is meant by a conservative field.
A conservative field is one where the work done by the force on a particle that moves through any round trip is zero i.e. energy is conserved.
explain why changing to a pike position reduces a gymnast’s angular momentum.
Mass (is now distributed) closer to the axis of rotation
State what is meant by angular velocity.
The rate of change of angular displacement.
State what is meant by torque:
Turning effect of a force.
What do scale uncertainties tell us about measuring instruments?
Systematic uncertainties when readings taken are either all too small or all too large. This can arise due to faulty measurement techniques or experimental
design.
Explain what is meant by gravitational potential.
The work done moving a unit mass from infinity to a point.
State what is meant by a geodesic.
The shortest distance between two points in curved spacetime.
What causes random uncertainties?
They arises when measurements are repeated, and slight variations occur. Random uncertainty may be reduced by increasing the number of repeated measurements.
State the escape velocity from the event horizon of a black hole.
Speed of light in a vacuum.
State what is meant by conservation of angular momentum.
Total angular momentum before an event is equal to the total angular momentum after an event in the absence of external torques.
State what is meant by luminosity.
The energy emitted per second by a star.
State what determines a star’s lifetime.
The star’s mass
Explain briefly how stars are formed.
Formed in interstellar clouds when gravitational forces overcome thermal pressure and cause a molecular cloud to contract until the core becomes hot enough to sustain nuclear fusion, which then provides a thermal pressure that balances the gravitational force).
Explain the difference between accuracy and precision.
Accuracy compares how close the measurement is to the ‘true’ or accepted value. The uncertainty in a measurement gives an indication of the precision of the measurement.
State the meaning of the term equivalence principle.
It is not possible to distinguish between the effects (on a body) of (uniform) acceleration and a (uniform) gravitational field.
State the change that will occur in the fusion reactions within the core of the Sun at the point when it leaves the main sequence.
Fusion (of hydrogen) (in core) stops.
Explain, in terms of gravitational force and thermal pressure, why the diameter of the Sun will increase as it becomes a red giant.
Outward forces caused by thermal pressure exceed gravitational
forces.
State what is meant by
Spacetime.
Unified representation of 3D space and 1D time.
State what is meant by the term Schwarzschild
Radius.
The distance from the centre of a black hole (singularity) to the event horizon.
