1.1Define Weight As the Force on an Object Due to a Gravitational Field

Physics:
Space

1 Weight and Gravity

1.1Define weight as the force on an object due to a gravitational field:

When an object comes in the vicinity of a larger mass such as a planet thelarger mass exerts a force on that object
This force is a gravitational force exerted due to the gravitational fieldsurrounding the object and is defined as Weight
Thus Weight is the force on an object due to a gravitational field
Formula:

W = Weight force (N)

W = mgm = Mass (kg)
g = Acceleration due to gravity (ms-2)

1.2 Define gravitational potential energy as the work done to move an object from a very large distance away to a point in a gravitational field:

Gravitational Potential Energy is the energy of a mass due to its positionwithin a gravitational field
On a larger scale it is defined as the work done to move an object from infinity to a point within a gravitational field
At infinity the gravitational potential energy is zero and decreases as a mass gets closer to the centre of a gravitational field
Formula:

Ep= Gravitational Potential Energy (J)

G = Gravitational constant (6.67x10-11)

m1 = Mass of Planet (kg)

m2 = Mass of Object (kg)

r = Distance between the two masses (m)

The negative sign occurs because the Gravitational Potential Energy of a mass as it approaches infinite distance from the Gravitational field is always negative.

1.3Explain that a change in gravitational potential energy is related to work done:

For Gravitational Potential Energy to change the object must move closer or further away from the centre of the gravitational field
Work must be done on the object to make this change in Distance
Thus a change in Gravitational Potential energy is related to work done

2 Projectile Motion

2.1 Describe the trajectory of an object undergoing projectile motion within the Earth's gravitational field in terms of horizontal and vertical components:

Galileo showed the vertical and horizontal motion of a projectile could be treated independently
To find the actual position and velocity the horizontal and verticalcomponents are added together

Projectiles:

Any object that is thrown, dropped or otherwise launched into the air
The object follows a parabolic path which, without factoring in resistance, is symmetrical
During flight the projectile experiences the force of gravity andacceleration due to Gravity

The Trajectory:

The path that a projectile follows during its flight
Can be broken down into two separate and independent motions:
Vertical Motion - affected by constantacceleration due to gravity
Horizontal Motion - experiences no acceleration

Vertical Motion:uy = u sinθ

The object, subjected to acceleration due to gravity, rises up, stops momentarily then falls down
When it hits the ground it is travelling at the same speed at which it left

Equations:

vy = uy+ ayt
vy2 = uy2 + 2ayΔy

Δy = uyt + ½ ayt2

Horizontal Motion:ux = u cosθ

When pushed horizontally, ideally, it experiences no acceleration in its direction of motion. Thus a projectile travels sideways in uniform motion

Equations:

vx = ux

Δx = uxt

3 Escape Velocity

3.1Explain the concept of escape velocity in terms of the gravitational constant and the mass and radius of the planet:

Definition: The minimum velocity required by an object to escape the gravitational pull of the Earth or other planet
Formula:

Explanation:
The above equation shows that Escape velocity depends only on the Gravitational Constant, Mass and Radius of the planet, not on any properties of the projectile
An object projected at this velocity would never come back down
During the rise the objects Kinetic Energy is converted into Gravitational Potential Energy

3.2Outline Newton's concept of escape velocity:

Diagram:

Explanation:
Newton predicted that an object projected horizontally from a highmountain would undergo projectile motion as shown in the above diagram
If the velocity of the projectile was increased enough, a speed would be reached where the object would fall around the Earth, i.e. orbit it.
If the speed exceeded the escape velocity the projectile would spiral away from the Earth

4 Galileo

4.1Describe Galileo's analysis of projectile motion:

Galileo showed that:

All masses fall at the same rate, regardless of weight
If Air Resistance is ignored, Acceleration due to gravity is the same for allobjects regardless of their mass
All projectiles move in a parabolic shape
Horizontal and vertical motion are separate; by using an inclined plane

5 G Forces

5.1 Identify why the term “g forces” is used to explain the forces acting on an astronaut during launch:

Definition: G force is a measure of acceleration force using the Earth’s gravitational acceleration as the unit.
A positive g force is one that is directed from the feet to the head (upwards), whereas a negative g force is in the other direction (downwards).
The sensation of feeling more weight than normal is a positive g force, whereas feeling less weight is due to negative g forces.
To help astronauts withstand extremely large g forces during lift-offs, they lie down and also special cushions are utilised. Fighter plane pilots wear ‘g suits’ to reduce the effect of the g forces when manoeuvring.
The forces experienced by Astronauts during launch are these g-forces.

6 Satellites

6.1Compare qualitatively low Earth and geo-stationary orbits:

Low Earth Orbits:

Orbital radii altitude between 200-2000km (less than those of geostationary orbits)
Orbital velocity of approximately 28000kmh-1(faster than geostationary orbits)
Mostly polar orbits (do not have a fixed position)
May orbit the Earth many times per day
Experiences orbital decay
Examples: Space Shuttle, Hubble Telescope

Geo-stationary Orbits:

Orbital radii altitude of approximately 35800km (higher than low Earth orbits)
Orbital velocity of approximately 11000kmh-1(slower than geostationary orbits)
The satellite appears to be stationary in the sky when viewed from the surface of the Earth
Their periods are the same as that of the Earth.
Does not experience orbital decay
Examples: Communications satellites, Weather satellites, Specialist Telescopes

6.2Account for the Orbital Decay of satellites in low Earth orbit:

Atmospheric drag caused by Earth's Atmosphere
Decays the orbit of a satellite by slowing it down causing it to lose altitude and slowly spiral towards the ground
Amount depends on density of Atmosphere and size of satellite
These satellites orbit at lower altitudes where the Atmosphere is more dense,thus these satellites experience higher levels of atmospheric drag than other satellites in higher orbits

6.3Define the term orbital velocity and the quantitative and qualitative relationship between orbital velocity, gravitational constant, mass of the central body, mass of the satellite and the radius of the orbit using Kepler's Law of Periods:

Definition of orbital velocity: The instantaneous speed and direction of an object in uniform circular motion along its path.
Formula:

V =

Kepler’s Third Law of Periods:

7 Re-entry

7.1Discuss issues associated with safe re-entry into the Earth's atmosphere and landing on the Earth's surface:

Extreme Heat:

Spacecraft has significant kinetic energy and gravitational potential energy
Spacecraft experiences friction with molecules of the atmosphere as it re-enters
The Spacecraft's Kinetic energy is converted into heat

Minimisation Techniques:

Blunt shape for re-entry, produces a Shockwave as it moves through the air, this shockwave absorbs most of the heat

Ablation - Covering with ceramic material which is vaporised (ablated)

Space shuttle covered with glass fibre tiles, 90% air

G Forces:

Greater angles of re-entry result in greater g-forces experienced by the astronaut
Humans cannot tolerate g-forces greater than 8g but 3g is the maximum advised

Increasing Tolerance:

Transverse application of g-load - astronauts lying down rather than upright
Astronauts Lift-off forwards, Re-enter backwards
Body supported in as many places as possible

Ionisation Blackout:

As heat builds up around the spacecraft, atoms in the air ionize forming a layer around the spacecraft
This layer causes a period of no communication with the spacecraft known as Ionization Blackout – approximately 4-16 minutes

Reaching the Surface:

Parachutes released in last portion of spaceships descent to slow it downbefore splashing into the ocean
Space shuttle has wings which allow the pilot to control its descent,underbelly provides blunt surface for protection

7.2Identify that there is an optimum angle for safe re-entry for a manned spacecraft into the Earth's atmosphere and the consequences of failing to achieve this angle:

The Re-entry Angle:

Optimum angle between 5.2o – 7.2o
Angle too shallow – spacecraft will bounce off
Angle too steep – spacecraft will burn up on re-entry

8 Uniform Circular Motion

8.1Analyse the forces involved in uniform circular motionfor a range of objects, including satellites orbiting the Earth:

Centripetal Force:

A centripetal force is required for objects to move in uniform circular motion
This force is always directed to the centre, perpendicular to the velocity of the moving object
Causes the object to continually change direction to follow a circular path

Formula:

Fc =

Examples:
Satellite orbiting the Earth - Centripetal Force comes from Gravitational attraction between Earth & the satellite
Car driving around the corner - Centripetal Force provided by friction between the tyres and the road

9 Earth’s Motion

9.1Discuss the effect of the Earth's orbital motion and its rotational motion on the launch of a rocket:

Rotational Motion:
Rockets launched from the equator, towards the east - takes advantage of Earth's Rotational Velocity
Leaves at its own velocity plus the velocity of the Earth's rotation
Orbital Motion:

To reach outer planets:

Launched in the direction of Earth's orbit, leaves at Earth's orbital velocity (30 kms-1) plus its own velocity.
Moves in an elliptical orbit allowing it to reach outer planets

To reach inner planets:

Launched in opposite direction, leaves at own velocity minus the Earth's
Moves in elliptical orbit closer to the sun allowing it to reach inner planets

10 Robert Hutchings Goddard

10.1Present information on the contribution of Goddard to the development of space exploration:

Measured the fuel values for various rocket fuels, such as liquid hydrogen and oxygen.
Launched the world’s first multi-staged liquid-fuel-powered instrument rocket.
Launched the first liquid-fuelled supersonic rocket.
Developed pumps for liquid fuels, as well as rocket engines that have automatic cooling systems.
Proved that a rocket will work in a vacuum, that it needs no air to push against (i.e. space).
Proposed and explained how the use of rocket propulsion could be used to reach high altitudes.

11 Changing Acceleration

11.1Analyse the changing acceleration of a rocket during launch in terms of the Law of Conservation of Momentum andthe forces experienced by astronauts:

Law of Conservation of Momentum:

“The total momentum of a closed system remains unchanged”

The momentum of the gases shooting out of the rear of the rocket is equal but opposite to the momentum of the rocket itself
Backward momentum of gases equal in magnitude to forward momentumof rocket
Since change in momentum = impulse (Ft), at any one second interval the backward force on the gases equals the forward force on the rocket
As the rocket moves, its mass decreases significantly, thus its velocity increases significantly (acceleration)

Forces Experienced by Astronauts:

Two forces acting on an astronaut during launch, upward thrust and downward weight force
If the thrust remains constant, the rate of acceleration of the rocket willincrease as itascends
Rockets mass also decreases as fuel burns and weight decreases at higheraltitudes

12 Universal Gravitation

12.1Describe a gravitational field in the region surrounding a massive object in terms of its effects on other masses in it:

Any mass, regardless of its size, will have a gravitational field around it
When a mass is placed within another masses gravitational field it will experience a force towards the massive object
This force of attraction is dependent on the mass of the objects and thedistance between them

12.2Define Newton's Law of Universal Gravitation & discuss the importance of Newton's Law of Universal Gravitation in understanding and calculating the motion of satellites:

Formula:

F = G

Description:
Newton believed that objects attract every other object in the universe
As shown in the formula above the attractive force's strength is determined by: the mass of the two objects, the distance between their centres
Motion of Satellites:
Occurs when centripetal force required to keep satellite moving in circular orbit equals gravitational attraction
When the gravitational attraction is greater than the centripetal force, the satellite spiralsinwards
When the gravitational attraction is less than the centripetal force, the satellite spirals outwards
Satellite orbiting closer to central planet has shorter orbital period and higher orbital velocity
Newtons Law of Universal Gravitation allows us to calculate gravitational force, orbital velocity and orbital periods of satellites

13 The Slingshot Effect

13.1Identify that a slingshot effect can be provided by planets for space probes:

The Slingshot Effect:

Involves moving a probe in a hyperbolic orbit to gain velocity from theGravitational Field
Probe approaches planet from in front, swung around by planet's gravity
Planet loses kinetic energy while the probe gains some

For space probes:

Sometimes employed by deep space probes to save fuel

As seen above, the space probe swings around the planet, changing direction and increasing speed. Vf > Vi

14 The Aether Model

14.1Outline the features of the aethermodel for the transmission of light:

The Aether Model:

19th Century - like all waveforms light needed a medium through which to travel
Called this medium the LuminiferousAether

Properties:

Filled all of space, stationary in space
Perfectly Transparent
Permeated all matter
Low Density
Great Elasticity

15 Michelson-Morley Experiment

15.1Describe andevaluate the Michelson-Morley attempt to measure the relative velocity of the Earth through the aether:

Analogy:

When you drive a car through the air, ‘wind’ is generated. The direction of the wind is in the opposite direction to the motion of the car.

The Experiment:

Designed to detect Aether using light and interference, with an interferometer (observer) on a turntable
Single beam of light split in half by half silvered mirror
One ray travelling across the Aether wind, another travelling through it, same distance & return
Because of the Aether wind produced by the moving Earth, light would be slowed down heading into it
When beams meet, interference pattern produced, should change as table is rotated through 90°
No such change, thus no difference in speed
Null result – no aether wind was detected

15.2Discuss the role of the Michelson-Morley experiments in making determinations about competing theories:

It provides experimental support for the theory of relativity

At the Time of the Experiment:

Did not sway scientific belief at the time of the Experiments
Null result seen as indication that the model needed improvement
Various modifications offered, each resulting in predictions failing to beproven

Einstein's Relativity:

Einstein proposed theory of relativity with its own predictions and it disproved the aether.
Important in helping others decide between the competing theories, alongwith comparative success of relativity experiments

16 Inertial Frames of Reference

An inertial frame of reference is one that is either stationary or moving with a constant velocity.

A non-inertial frame of reference is one that is undergoing acceleration.

16.1Outline the nature of inertial frames of reference:

Galileo showed that there is no difference between standing still and moving at constant velocity in a straight line - basis of Newton's First Law of Motion (inertia)
An inertial Frame of Reference is one in which Newtons First Law is obeyed. These are at rest or moving with a constant velocity
They involve no acceleration

16.2Discuss the principle of relativity:

Principle of Relativity: All steady motion is relative and cannot be detected without reference to an outside point
Principle applies only to inertial frames of reference
Within an inertial frame of reference you cannot perform any experimentto detect your motion without referring to another frame of reference

16.3Describe the significance of Einstein's assumption of the constancy of the speed of light & identify that if c is constant then space and time become relative:

The Speed of Light:

The speed of light has to be constant for the Principle of relativity to holdtrue
If the speed of light were not constant, differing speeds of light in differentframes of reference could be used in determining our motion
Thus violating the Principle of Relativity

Relative Space & Time:

Classic physics - space (position, displacement, velocity etc) are relative to an observer, time is absolute passing identically for everybody
Theory of Relativity - for speed of light to be constant time and space must both be relative
Time passes differently for different observers depending on their relative motion
Showed that there is no absolute frame of reference, all are equivalent

17 Consequences of Special Relativity

17.1Explain qualitatively and quantitatively the consequence of special relativity in relation to:

Relativity of Simultaneity:

Two events judged by one observer to be simultaneous, not generally judged to be simultaneous by other observer in different frame of reference in relative motion
Whether or not two events are seen to be simultaneous depends onposition relative to the two events

Equivalence between Mass & Energy:

Mass can be converted to energy and energy can be converted to massunder extraordinary circumstances
Equation; E = mc2 expresses equivalence between mass and energy
Law of Conservation of Energy and Law of conservation of mass replacedby Law of conservation of Mass-Energy

Length Contraction:

Length of an object measured within its rest frame is called it's proper length (Lo)
Observers in other frames of reference in relative motion always measurethis length (Lv) to be shorter

Time Dilation:

Time taken for event to occur within it's rest frame is called proper time (to)
Observers in different reference frames in relative motion always judge the time taken (tv) to be longer