Mod 5 Flashcards
Define Uniform Circular Motion (UCM)
Uniform Circular Motion is when an object travels in a circle at a constant rate
Identify features of Uniform Circular Motion (UCM)
Features of Uniform Circular Motion:
- Constant speed
- Constant acceleration - magnitude
- Constant force
- Changing direction of velocity
- Zero displacement
- Fixed centre and radius
- Zero net force
Identify the driving force for Uniform Circular Motion (UCM)
Centripetal force drives uniform circular motion
Centripetal Acceleration
a = (v^2)/r
Centripetal Force
F = (mv^2)/r
Explain why centripetal force is not drawn in force diagrams
In uniform circular motion, centripetal force is the net force and hence, is not drawn in force diagrams
True or False. Calculations of Uniform Circular Motion (UCM) has to be performed in radians
True. Using degrees will result in incorrect solutions
Linear velocity - UCM
v = r * ω
Angular velocity - UCM
ω = (2π)/T
True or False. Conical Pendulum is an example of Uniform Circular Motion (UCM)
True. Note: It is only uniform circular motion if the motion of the weight forms a circle - hence, or ‘conical’
Define banked track
A track with a tilt towards the centre to assist in turning
Compare and contrast banked tracks with a slope
Although both are inclined, a bank track = N > mg and a slope = N < mg
Define torque
Torque is the rotational effect that a force has on an object
Identify whether torque is a vector or scalar quantity
Torque is a vector quantity. Torque is the cross-product of 2 vector quantities
Torque
Τ = rFsin(θ)
True or False. An object with no net force has no net torque
False. Force is linear and torque is rotational - hence 2 separate components
Define rotational equilibrium
Rotational Equilibrium is when the net torque = 0; there is no overall rotational effect within the system
Define inertia
Inertia refers an object’s tendency to resist motion
Inertia
I = mr^2
Define orthogonal
Orthogonal is when vectors are perpendicular in 3D space
Define critical speed
Critical speed is when under zero friction the minimum speed necessary to remain in uniform circular motion
Gravitational Force
F = (Gm1m2)/(r^2)
Explain why the force between masses is the same regardless of individual masses
The force is equal due to Newton’s Third Law of Motion - equal and opposite forces
Gravitational Field Strength
g = (GM)/(r^2)
Define mass
Mass is the amount of particles in an object
Define weight
Weight is the gravitational attraction force acting upon a body’s mass
True or False. Gravitational field lines only facilitate attraction force.
True.
Identify the factors that impact gravitational strength
Factors that impact gravitational strength:
1. Earth is not an oblate spheroid
2. The surface is not uniform
3. The density of the Earth is not uniform
4. Psuedo Effect
Outline the Psuedo Effect
The Psuedo Effect occurs due to the rotation of the Earth which counteracts the normal force, creating the perception of weaker gravitational strength.
Identify where the Psuedo Effect is most evident. Elaborate
The Psuedo Effect is most evident at the equator as the radius of the Earth is most significant
Outline the derivation of critical speed
Net force = 0
Both the vertical and horizontal components = 0, hence:
equate - v^2 = rg tan(θ)
Outline the derivation of orbital velocity
As the gravitational force supplies the centripetal force, equate:
v^2 = (GM)/r
Identify what you notice about the orbital velocity. Elaborate.
The mass of the orbiting object is not a factor in velocity. This can be explained through the conservation of energy as the kinetic energy is transferred into gravitational potential energy and the ‘m’ is cancelled out.
State Kepler’s 1st Empirical Law
Orbits about the sun are elliptical where the sun is located at one of the two foci
State Kepler’s 2nd Empirical Law
The line between the orbiting object and the object being orbited sweeps out equal area for a given time interval.
Kepler’s 3rd Empirical Law
(r^3)/(T^2) = (GM)/(4π^2)
Identify the types of Earth orbits
Types of Earth Orbits:
- Lower Earth Orbit (LEO)
- Geostationary Orbit
- Geosynchronous Orbit
Discuss the advantages and disadvantages of Lower Earth Orbit
Advantages:
- Not significant energy necessary
- Can clearly monitor Earth’s surface
- Insignificant signal delay
Disadvantages:
- Orbital decay
- Satellite dishes have to rotate and coordinate with the satellites
Define orbital decay
Orbital Decay is the collisions between the molecules in the upper reaches of the atmosphere and the satellite, creating significant drag force
Define geostationary orbit
Geostationary orbit is at an altitude of 35, 780 km, precisely matching the period of the orbits with the Earth - appearing above the same point on Earth at all times
Compare and contrast geostationary orbit and geosynchronous orbit
Although both are at the same altitude - 35, 780km - a geostationary orbit is in the equatorial plane and a geosynchronous orbit is not and it forms a figure-8 shape instead
Explain why the gravitational potential energy is always negative
Gravitational potential energy is always negative as an infinite distance away is considered the Zero Reference Point
Gravitational Potential Energy
U = -(GMm)/r
True or False. Gravitational potential energy is of a significant value close to planetary masses. Link visually
False. Gravitational potential energy is of an insignificant value close to planetary masses. This is depicted through ‘potential wells’ graphically
Derivation of Total Mechanical Energy
TME = KE + GPE
Use orbital velocity - hence limited to orbital motion
TME = -(GMm)/(2r)
Define escape velocity
Escape velocity is the minimum speed at which an object needs to be launched from the surface in any direction such that it will completely exit the gravitational field
Derivation of escape velocity
Equate the change in kinetic energy and gravitational potential energy, where initial kinetic energy = 0 and final gravitational potential energy = 0
v^2 = (2GM)/r
True or False. The escape velocity of an object is independent of its mass
True
Identify the shape of the flight of an object below escape velocity
Shape of Flight:
- Ellipse
- Circle
Identify the shape of the flight of an object exceeding escape velocity
Shape of Flight:
- Parabola
- Hyperbola
Identify the types of orbital transfer manoeuvre
Movement between orbits:
- Low to High
- High to Low
Define perigee
The point in the orbit nearest to the planetary mass based on geometric centre
Define periapsis
The point in the orbit nearest to the planetary mass based on density core
Define apogee
The point in the orbit furtherest to the planetary mass based on geometric centre
Define apoapsis
The point in the orbit furtherest to the planetary mass based on density core
Compare and contrast weightlessness and apparent weightless
Weightlessness is when gravity does not act on an object; g = 0. Apparent weightlessness is when the object cannot feel the sensation of weight; the normal force = 0.
Define artificial gravity
In the absence of gravity, the sensation of gravity can be evoked (N = g)
