Space Flashcards
acceleration due to gravity equation:
g = Gm/(r^2)
m and r and both of the planet
orbital velocity?
escape velocity?
orbital velocity:
v= square root of (GM/r)
= [2(pi)r]/t
escape velocity:
v=square root of (2GM/r)
prac to measure ‘g’
Pendulum prac:
Method:
1) set up a pendulum
2) measure 10 periods of small amplitude swings and divide by 10 to find the period (T)
3) repeat with different length pendulum
Results:
As the period of a pendulum is related to its length via:
T= [(2pi) times the square root of (l/g)]
When T^2 vs length is graphed it gives a linear relationship and via the equation above T^2/l = [4(pi^2)]/g
i.e. the gradient of the graph
Galileo’s analysis of projectile motion:
Galileo’s analysis of projectile motion is that the motion of a body can be split into two components,
horizontal and vertical.
projectile:
-constant horizontal velocity
-constant vertical acceleration
Therefore=parabolic arc
g-force:
The term ‘g force’ is used to express a person’s apparent weight as a multiple of their normal true
weight as they’re in a non-inertial (accelerating) frame.
g force = (apparent weight)/(true weight)
Effect of the Earth‘s orbital motion and its rotational motion on the launch of a rocket:
When a rocket is launched from
Earth the horizontal velocity of the rocket will be the same as the rotational speed of the Earth plus
the orbital motion of Earth.
Rotational V:
For max velocity boost launch rocket at the equation and towards the east.
Orbital V:
Not important when launching a satellite into to orbit Earth but when launching an object beyond this point the position and direction of earths orbit around the sun wildly effects rocket’s V in reference to its target location. For max V launch when Earth’s trajectory is pointing towards the target.
Analyse the changing acceleration of a rocket during launch in terms of the:
– Law of Conservation of Momentum
– forces experienced by astronauts
Law of Conservation of Momentum:
The momentum (𝑝 = 𝑚𝑣) of a rocket during launch is conserved. As fuel is burnt and the gasses
expelled, the mass of the rocket decreases. But as momentum is conserved, velocity must
increase at the same rate that mass is decreasing. So as velocity of the rocket is increasing the
rocket must be accelerating.
As fuel is burnt, it is expelled as exhaust with a change in momentum (MfVf). To conserve momentum, the change in momentum (impulse), DOWN for the exhaust produces an equal and opposite change in momentum (impulse) Up to the rocket (MrVr)
i.e. MfVf= -MrVr
Forces Experienced by Astronauts:
F= thrust - weight(=mg)
As the rocket moves up it expels fuel (-m) and gravity weakens (-g) therefore force felt by the astronaut increases as the rocket accelerates.
Newton’s Laws:
1) An object at rest tends to stay at rest, an object in motion tends to stay in motion, unless acted on by a net force.
2) F=ma
3) every action has an equal and opposite reaction
Problems with re-entry:
Ballistic pods:
have to enter the atmosphere between 5 and 7 degrees.
7- burn up from the friction and decelerate too fast, g-forces felt by astronauts would be large.
Ballistic pods are heat shields that melt during re-entry taking heat away from the pod.
-Lands using a parachute.
Space Shuttle:
Uses S turns to ‘wipe off’ KE, not allowing it to decelerate too fast on re-entry.
-Uses silica heat tiles to protect the air frame.
-Lands like an aircraft.
identify that a slingshot effect can be provided by planets for space probes:
The slingshot effect allows satellites to change speed and direction. The change in direction is due to
the gravitational field which applies a force to the space probe which changes its direction. The
satellite can also be sped up or slowed down. An increase in speed is because, relative to the sun,
the passing space probe has gained velocity from the moving planet. Gravitational slingshots involve
gravitational potential energy being converted into kinetic energy. Some of the angular momentum
and kinetic energy of the planet is transferred to the space probe.
Michelson-Morley Experiment:
Aim: To measure the relative velocity of the Earth through the aether.
Method:
- light source at the bottom fired up
- half silvered mirror at 45degrees in the middle
- 2 mirrors at the top and right
- screen on the left where beams meet and interference pattern could be seen (or couldnt).
Result:
Null result. No evidence there is no relative motion between the aether and Earth.
-Actually no aether, light moves without a medium and at the same speed in all inertial frames.
Significance of Einstein’s assumption of the constancy of the speed of light:
The significance of this constancy of the speed of light is that time and space must be relative. This
means that time and space (time, mass, length) must change depending on your speed.
relativity of simultaneity:
If two events appear simultaneous in one frame of reference, they are not necessarily simultaneous
in another frame of reference.
Special Relativity:
The Newtonian laws of physics are the same for all non-accelerating observers, and he showed that the speed of light within a vacuum is the same no matter the speed at which an observer travels.
Thought experiment:
‘If it were possible to travel on a train at the speed of light would i see my reflection in a mirror?’ To answer no would violate the principle of relativity as laws of electromagnetism do not all for light to be stationary. This line of reasoning for the postulate of the constancy of the speed if light.
Test for inertial and non-inertial planes:
pendulum on a platform:
If its still or in uniform motion the pendulum hangs straight down.
When accelerated pendulum swings backwards (i.e. not straight don bc non-inertial)
