Dynamics and Space Flashcards

1
Q

State what is meant by the term escape velocity:

A

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.

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2
Q

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.

A

The angular velocity increases so the required centripetal force increases

until the friction is insufficient (to hold the stone in place)

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3
Q

State what is meant by moment of inertia.

A

A measure of an objects resistance to angular acceleration about an axis.

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4
Q

Explain why systematic uncertainties occur.

A

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.

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5
Q

State what is meant by gravitational field strength.

A

The gravitational force exerted per unit mass.

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6
Q

State what is meant by a world line:

A

Line that represents an object on a spacetime diagram.

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7
Q

What will a distance observer notice about time at the event horizon of a black hole?

A

Time will appear to be frozen.

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8
Q

Explain what is meant by a calibration uncertainty.

A

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.

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9
Q

State what is meant by apparent brightness.

A

The brightness of a star as measured on
Earth.

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10
Q

Explain what is meant by a non-inertial frame of reference.

A

Frames of reference that are accelerating (with respect to an inertial frame).

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11
Q

State what is meant by the phrase gravitational lensing.

A

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.

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12
Q

Explain why electrons follow a curved path between parallel deflection plates.

A

The electrons travel with constant) horizontal velocity.

Electrons travel with (constant) vertical acceleration.

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13
Q

A car is travelling around a circular track at a constant speed. Explain why it is accelerating.

A

The car’s direction/velocity is changing. OR
Unbalanced/centripetal/cen tral force acting on the car.

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14
Q

Explain briefly what happens when the hydrogen in a star’s core is depleted.

A

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

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15
Q

Explain what is meant by a conservative field.

A

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.

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16
Q

explain why changing to a pike position reduces a gymnast’s angular momentum.

A

Mass (is now distributed) closer to the axis of rotation

17
Q

State what is meant by angular velocity.

A

The rate of change of angular displacement.

18
Q

State what is meant by torque:

A

Turning effect of a force.

19
Q

What do scale uncertainties tell us about measuring instruments?

A

Scale reading uncertainties are an indication of how precisely an instrument scale can be read.

20
Q

Explain what is meant by gravitational potential.

A

The work done moving a unit mass from infinity to a point.

21
Q

State what is meant by a geodesic.

A

The shortest distance between two points in curved spacetime.

22
Q

What causes random uncertainties?

A

They arises when measurements are repeated, and slight variations occur. Random uncertainty may be reduced by increasing the number of repeated measurements.

23
Q

State the escape velocity from the event horizon of a black hole.

A

Speed of light in a vacuum.

24
Q

State what is meant by conservation of angular momentum.

A

Total angular momentum before an event is equal to the total angular momentum after an event in the absence of external torques.

25
Q

State what is meant by luminosity.

A

The energy emitted per second by a star.

26
Q

State what determines a star’s lifetime.

A

The star’s mass

27
Q

Explain briefly how stars are formed.

A

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).

28
Q

Explain the difference between accuracy and precision.

A

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.

29
Q

State the meaning of the term equivalence principle.

A

It is not possible to distinguish between the effects (on a body) of (uniform) acceleration and a (uniform) gravitational field.

30
Q

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.

A

Fusion (of hydrogen) (in core) stops.

31
Q

Explain, in terms of gravitational force and thermal pressure, why the diameter of the Sun will increase as it becomes a red giant.

A

Outward forces caused by thermal pressure exceed gravitational
forces.

32
Q

State what is meant by
Spacetime.

A

Unified representation of 3D space and 1D time.

33
Q

State what is meant by the term Schwarzschild
Radius.

A

The distance from the centre of a black hole (singularity) to the event horizon.