Our Dynamic Universe Flashcards
Definitions from Higher Physics unit 1
What is meant by a Scalar?
Magnitude (size) only
What is meant by a Vector?
Magnitude and a direction
What is meant by “Distance”?
The length of the route taken (magnitude only)
What is meant by “Displacement”?
The straight line length from start to end of a motion (magnitude & direction).
What is meant by “Direction by compass point”?
An angle from a compass point with a direction.
eg ‘43 degrees West of North’.
What is meant by “Direction by Bearing”?
A three figure angle clockwise from North. eg ‘bearing of 317’.
How do you calculate the speed of an object?
Scalar : speed = distance / time
How do you calculate the magnitude of the velocity of an object?
Vector : velocity = displacement / time
What is meant by Acceleration?
The change in velocity of an object in 1 second.
What is meant by “Positive acceleration”?
Velocity increasing
What is meant by “Negative acceleration”?
Velocity decreasing
How do you find the distance travelled from a v-t graph?
Calculate the area under the graph.
What is Newton’s First Law?
An object will remain at rest or travel in a
straight line with a constant speed, unless
an unbalanced force acts upon it.
What is Newton’s Second Law?
An unbalanced force acting on an object
will cause the object to accelerate. The size
of that acceleration will depend on the size
of the force and the mass of the object.
What is Newton’s Third Law?
If object A applies a force on object B, then
object B applies and equal but opposite force on A.
What is meant by the “Mass” of an object?
The amount of matter within an object.
The value does not change with position
What is meant by the “Weight” of an object?
The force due to gravity on a mass.
The value does change with position
Describe the Horizontal motion of a Projectile.
Constant horizontal velocity
Describe the Vertical motion of a projectile.
Constant vertical acceleration
What is the component of weight acting down a slope?
mgsinθ
State the “Law of conservation of momentum”.
The total momentum before a collision is equal to the total momentum after a collision in the absence of external forces.
What is meant by an “Elastic collision”?
A collision in which both momentum and kinetic energy are conserved.
What is meant by an “Inelastic collison”?
A collision in which momentum is conserved, but kinetic energy is lost.
What is meant by an “Inelastic explosion”?
A collision in which momentum is conserved, but kinetic energy increases.
What is meant by “Impulse”?
The change of momentum of an object in a collision.
How do you find the change in momentum from a F-t graph?
Calculate the area under the graph.
What is meant by Orbital Period?
The time taken for a satellite to complete one full orbit.
What is meant by Geostationary Orbit?
A satellite with an orbital period of 24 hours. This causes the satellite to appear stationary relative to a point on the Earth’s surface.
What is meant by “Gravitational field strength”?
The force experienced by a unit mass (1kg) at that point in a gravitational field.
What is meant by “Gravitational Force”
The Force between two objects with mass. It is proportional to magnitude of the masses, and inversely proportional to the square of the radius between them.
What is meant by a “Inertial frame of reference”?
A description of a fixed point from which all other measurements are taken.
What conditions are required for Special Relativity to apply?
- Objects must be moving at a constant velocity relative to each other.
- The magnitude of the relative velocity must be larger that ~10% of the speed of light.
What are the two fundamental rules for Special Relativity?
- When two observers are moving relative to each other, they will observe the same laws of Physics within their own frames of reference.
- The speed of light is the same for all observers, regardless of their motion relative the the light source.
What simple statement acts as a reminder of “Time dialation”?
“Moving clocks run slow”
What simple statement acts as a reminder of “Length contraction”?
“Moving objects are short”
State a real-world example of “Time dilation”.
GPS Satellites - Thier clocks run at a slower rate due to their realtive motion, without correction the system would rapidly lose accuracy.
State a real-world example of “Length contraction”.
Muon Decay - Due to length contraction, the height of the atomsphere is reduced in a Muon’s frame of reference, allowing the Muon to travel further before decaying.
What is meant by “Doppler shift”?
The apparent change in frequency of an emitted wave due to relative motion between the source and observer.
Which variant of the Doppler relationship is used when the source is moving away from the observer?
V + Vs
Which variant of the Doppler relationship is used when the source is moving towards the observer?
V - Vs
What is meant by a “Continuous spectrum”?
A unbroken spectrum showing all wavelengths.
What is meant by a “Line Absorbion spectrum”?
A spectrum with certain frequencies have been absorbed in the Sun’s outer atmosphere, leaving dark gaps in the spectrum.
What is meant by a “Line Emission spectrum”?
A spectrum showing only certain frequencies, which correspond to energy transitions within the atoms of that element.
What is meant by the “Peak wavelength” of a star?
The wavelength at which a star emits the most radiation. It is the highest point in the star’s black body curve.
What is the relationship between the temperature of a star and its peak wavelength?
As the temperature increases, the peak wavlength becomes shorter. (Hot blue stars, cool red stars)
What is the relationship between the temperature of a star and its “Emitted radiation per unit surface area per unit time”?
As the temperature increases, the emitted radiation per unit surface area per unit time increases.
What is meant by “Redshift”?
The light from objects moving away from us is shifted to longer wavelengths (red end of the spectrum).
What is meant by “Blueshift”?
The light from objects moving towards us is shifted to shorter wavelengths (blue end of the spectrum).
How does the Hubble-Lemaître Law allow an estimation the age of the Universe?
By combining the formula for the Hubble-Lemaître law with the formula for velocity, the age of the Universe can be calculated.
How does the Hubble-Lemaître Law lead to the theory of the expanding universe?
The Hubble-Lemaître Law shows that the speed of recession increases with distance, the only explanation that Hubble could derive from this data was that the Universe was expanding.
How can the mass of a galaxy be estimated?
The mass can be estimated by the orbital speed of the stars within it.
What is meant by “Dark matter”?
Matter that is undetectable through current technology. Evidence for dark matter comes from the measured masses of galaxies.
What is meant by “Dark energy”?
Energy that is acting to accelerate the expansion of the universe against the effects of gravity. Evidence for dark energy comes from observations of the most distant observable supernovae.
How does the “Cosmic microwave background radiation” provide evidence of the Big Bang theory?
The CMBR was emitted during the early universe. At the time of emission, the photons had a much shorter wavelength, but due to the expansion of the Universe, these photons have experienced redshift and now are observable only in the microwave region.
How does the “Abundance of hydrogen & helium” provide evidence of the Big Bang theory?
The abundance of hydrogen & helium can be explained by their formation in the very early universe when the entire universe was hot and dense enough for these to form through fusion.
How does “Olber’s Paradox” provide evidence of the Big Bang theory?
“In an infinitely old Universe with an infinite number of stars distributed in an infinitely large volume, the night sky would be bright, not dark.” As the night sky is dark, the universe must be finite in size or age.
