Space - Core Flashcards
What is gravitational potential energy?
It is the energy of a mass due to its position within a gravitational field. On a large scale, gravitational potential energy is defined as the work done to move an object from infinity (or some point very far away, to a point within a gravitational field
On Earth, what is the gravitational field strength g?
9.8m.s-2
At infinity, what is Ep defined as?
Zero
What is a projectile?
Any object moving under the influence of gravity only.
What are the two independent motions of projectile motion?
The horizontal (x) component and the vertical (y) component.
What is escape velocity?
It is the velocity needed for an object to escape from the Earth (or other planet or moon).
What does escape velocity depend on?
The mass of the planet or moon and the gravitational constant, G.
What is the trajectory of a projectile?
It is the path that it follows during its flight.
What is thrust?
Thrust is the force delivered to a rocket by its engines.
What is uniform circular motion?
It is circular motion with a uniform orbital speed
What is centripetal force?
It is the force that acts to maintain circular motion and is directed towards the centre of the circle.
When is centripetal acceleration present?
Always in uniform circular motion. It is also associated with centripetal force and is also directed towards the centre of the circle
What is orbital velocity?
It is the instantaneous direction and speed of an object in circular motion along its path.
What is a LEO?
LEO stands for low Earth orbit and it is an orbit higher than 250km and lower than 1000km.
What is a geostationary orbit?
A geostationary orbit is at an altitude at which the period of the orbit precisely matches that of the Earth. This corresponds to an altitude of approximately 35800km.
What is the slingshot effect, or planetary swing-by or gravity assist manoeuvre?
It is a strategy used with space probes to achieve a change in velocity with little expenditure of fuel.
What is the first phase of the de-orbit manoeuvre?
It is to alter the spacecraft’s orbit into a transfer ellipse that intersects the atmosphere at the desired angle.
With re-entry, why is a shallow angle selected?
To minimise the extreme heating and g forces that can destroy a spacecraft on an uncontrolled re-entry. However, if the angle is to shallow, the spacecraft may skip off the atmosphere instead of penetrating it.
Why is it that re-entry produces so much heat?
Consider that the spacecraft has a velocity of tens of thousands of kilometres per hour. This velocity means that the spacecraft has significant kinetic energy. Additionally, the altitude of the spacecraft’s orbit means that it also has considerable gravitational potential energy, which is also lost as the spacecraft’s altitude decreases during re-entry. As the spacecraft re-enters, it experiences friction with the molecules of the atmosphere. This friction is a force directed against the motion of the spacecraft and causes it to decelerate; that is, to slow down. The enormous kinetic energy the spacecraft possesses is converted into heat, and that heat can cause the spacecraft to reach extreme temperatures.
What is Ionisation blackout?
It is a period of no communication with a spacecraft due to a surrounding layer of ionised atoms forming in the heat of re-entry
What is a gravitational field?
It is a field within which any mass will experience a gravitational force. The field has both strength and direction.
What was the aether?
It was the proposed medium for light and other electromagnetic waves, before it was realised that these waveforms do not need a medium in order to travel.
What is a medium?
It is the material through which a wave travels
What is an inertial frame of reference?
It is a non-accelerated environment. Only steady motion or no motion is allowed.
What is a non-inertial frame of reference?
It is a frame of reference which experiences acceleration.
What is a rest frame?
It is the frame of reference within which a measured event occurs or a measured object lies at rest.
What is time dilation?
It is the slowing down of events as observed from a reference frame in relative motion.
What is length contraction?
It is the shortening of an object in the direction of its motion as observed from a reference frame in relative motion.
What is mass dilation?
It is the increase in the mass of an object as observed from a reference frame in relative motion.
What is rest energy?
It is the energy equivalent of a stationary object’s mass, measured within the objects rest frame.
